While most snakes are completely harmless, some inspire dread for good reason. Globally, 5.4 million people are bitten by snakes every year, resulting in between 80,000 and 140,000 annual deaths, according to the World Health Organization.

Of the 4,000 snake species in the world, only about 600 are venomous, though not all of those pose a threat to humans. That doesn't stop some people from developing ophidiophobia, or an intense fear of snakes, which is one of the most common phobias.

Without further ado, how much do you know about snakes?

Remember to log in to put your name on the leaderboard; hints are available if you click the yellow button, and let us know your score in the comments. Good luck!

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"Twins! She has another baby," Judith Pardo-Pérez, a paleontologist at the University of Magallanes in Chile who first discovered the fossil in 2009, told Live Science, adding that she plans to release more details of this discovery in a forthcoming research paper.

Sixteen ago, researchers working in southern Chile's Torres del Paine National Park struck paleontological gold, unearthing the fossilized remains of a pregnant ichthyosaur — a dolphin-like predator that patrolled the seas for most of the Mesozoic era (252 million to 66 million years ago).

The ichthyosaur was preserved in exquisite detail, and included the approximately 6-inch-long (15 centimeters) skeleton of an unborn fetus, the researchers initially reported.

The fossil was first discovered in 2009 when Pardo-Pérez was working as a doctoral student. When she returned to the site a year later, she noticed unusual bones between the ribs of the main fossil, indicating the presence of a fetus — but it wasn't until 2022 that the pregnant ichthyosaur, dubbed Fiona, was fully excavated.

Now, Pardo-Pérez and colleagues have carried out a full analysis of the fossil. Their findings were published Feb. 25 in the Journal of Vertebrate Paleontology.

Related: The world's largest ichthyosaur may have just been discovered in the Swiss Alps

The ichthyosaur, which lived approximately 131 million years ago, is estimated to have been around 11.5 feet (3.5 meters) long. Its remarkable preservation is attributed to the rapid burial of the carcass in sediment, coupled with a lack of scavengers, likely due to low oxygen levels on the seafloor, according to the study. Researchers identified it as Myobradypterygius hauthali, a species previously known from other fragmentary remains.

This find represents the third instance of a pregnant ichthyosaur from the Cretaceous period (145 million to 66 million years ago), although pregnant ichthyosaurs dating to the Jurassic and Triassic periods have also been found. The fetus' vertebrae, measuring approximately 0.6 inches (1.5 cm) in height, are surprisingly large in proportion to Fiona's 11.5-foot length. The researchers feel that M. hauthali may have given birth to relatively large babies.

Although some earlier ichthyosaurs pushed their newborns out head first, Fiona's remains suggest otherwise. The orientation of the fetus inside Fiona suggests that, like many evolutionary "advanced" ichthyosaurs, M. hauthali delivered its young tail first, an adaptation also seen in modern dolphins and whales.

The researchers also uncovered Fiona's last meal: the remains of small fishes. This is a rare glimpse into the dietary habits of Cretaceous ichthyosaurs, as direct evidence of their meals is uncommon.

Pardo-Pérez is continuing to analyze the pregnant ichthyosaur and has performed a CT scan of the fossil, allowing her to observe the entire skeleton in greater detail. It was then that she discovered that the ichthyosaur was pregnant with twins, and she plans to publish a new study on these findings in the future.

The animals' fossilized remains, uncovered across four excavations between 2014 and 2019, have been relatively undisturbed since then and feature preserved delicate small bones and parts of the creatures' overall skeletal structure. The well-preserved findings could provide insight into how these Triassic amphibians lived and grew up, researchers reported in a new study published Wednesday (April 2) in the journal PLOS One.

Study first author Aaron Kufner, a geologist at the University of Wisconsin-Madison, and colleagues uncovered fossils of Buettnererpeton bakeri in a Wyoming fossil bed called Nobby Knob. These alligator-size creatures belong to an ancient amphibian group known as metoposaurids, a family of large, primitive four-legged amphibians. B. bakeri is the oldest known North American metoposaurid. It lived during the Triassic period (252 million to 201 million years ago) and may have frequented freshwater lakes and rivers as breeding grounds.

It's fairly common to find large piles of bones, known as bone beds, in the fossil record. Typically, bone beds occur when flowing water deposits bones in the same place over many years. Other times, bone beds happen when a group of animals die at the same time and place — which appears to be the case at Nobby Knob.

"This assemblage is a snapshot of a single population rather than an accumulation over time," Kufner said in a statement. The discovery "more than doubles the number of known Buettnererpeton bakeri individuals." Alongside the B. bakeri fossils, the team also found fossilized plants, bivalves and fossilized poop, called coprolites.

The amphibian bones didn't show any signs of having been moved by flowing water, suggesting these creatures came to rest in or near calm waters and were slowly buried by fine sediments during repeated floods. This left some of the fossils in the same shape and arrangement as the animals' actual skeletons. The researchers found B. bakeri fossils of various sizes, which could help explain how the animals grew and aged.

Because the closely grouped bones weren't carried to the site by currents, the researchers suspect the animals perished around the same time. They may have been part of a breeding colony or died because they were somehow prevented from leaving a drying body of water they needed to survive, the team suggested. It's still unclear whether mass metoposaurid die-offs like the one at Nobby Knob were common during the Triassic or whether the site represents an isolated event.

The B. bakeri fossils could help scientists date other metoposaurid fossils, the researchers wrote in the study. The Buettnererpeton fossils were buried deeper than fossils of Anaschisma browni, another metoposaurid, in the Popo Agie Formation — a Triassic formation that spans parts of Wyoming, Colorado and Utah. The finding that the Buettnererpeton fossils were likely older than Anaschisma correlates with other fossil beds that preserve both species and help date the regions and depths at which those fossils were found.

The Nobby Knob bone bed "preserves a wide size range of individuals from a single site that can provide insight into the [development] of metoposaurids," the scientists wrote in the study.

Bears are a type of mammal that can be found in many parts of the world. From the tiny, silly-looking sun bear to the iconic polar bear, these animals are specially adapted to different environments, including forests, mountains, icy tundra, deserts and swamps. Though there are different types of bear, all bear species have similarities. They all have stocky, fur-covered bodies; short legs; and a round head with a long snout. Whether the word "bear" makes you think of a fierce predator or a cuddly stuffed toy, there's plenty to discover about the science behind this diverse group of mammals.

5 fast facts about bears

• Panda bears poop 40 times per day.
• When they're first born, bear cubs weigh less than 2 pounds (0.9 kg).
• Bears that snack on honey have thick skin and fluffy fur that protects them against bee stings.
• Because polar bears spend so much time on the water, they're classified as marine mammals.
• Bears have a great sense of smell that helps them sniff out food.

Everything you need to know about bears

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Whereas lone star ticks are found mainly in the southern and eastern U.S., black-legged ticks (Ixodes scapularis), also called deer ticks, are present in the eastern half of the U.S. and the Midwest and the western black-legged tick (Ixodes pacificus) inhabits the West Coast, according to Mayo Clinic.

The new case reports suggest that people in a wide swath of the U.S. are at risk of tick-borne alpha-gal syndrome. However, "evidence continues to support that in the U.S., most alpha-gal syndrome patients develop the allergy after experiencing a bite from a lone star tick," Dr. Johanna Salzer, a veterinary medical officer and epidemiologist with the Centers for Disease Control and Prevention's (CDC) Division of Vector-Borne Diseases and a co-author of both case reports, told Live Science in an email.

Given that a variety of tick species have been linked to alpha-gal syndrome outside the U.S., scientists had long suspected that black-legged ticks in the U.S. also transmit the allergy.

"For us, it was never just the lone star tick," Jennifer Platt, co-founder of the nonprofit Tick-Borne Conditions United and an adjunct faculty member at the University of North Carolina at Chapel Hill, wrote in a blog post. "With thousands of Lyme [a tick-borne disease] patients telling us they can't tolerate red meat, we've long suspected black-legged ticks and other tick species in the US," she noted.

"Although our publications are some of the first reports linking blacklegged ticks in the US to alpha-gal syndrome, bites from these species in the U.S. leading to alpha-gal syndrome almost certainly have occurred prior to these reports," Salzer said.

In alpha-gal syndrome, the immune system overreacts to a sugar known as galactose-α-1,3-galactose, or "alpha-gal" for short. Those affected can develop severe allergic reactions not only to red meat but also to some medications, personal care products, and medical treatments containing ingredients from mammalian tissues, where this sugar is found.

Related: Tick season: What to know about bites, removing ticks and tick-borne diseases

The first case, reported in the April 4 issue of the CDC journal Emerging Infectious Diseases, described a Maine woman who developed alpha-gal syndrome after a confirmed black-legged tick (I. scapularis) bite.

The 45-year-old woman first experienced inflammation and itchiness at the bite site, followed by abdominal pain and malaise nine days later, after eating rabbit. Over the next two weeks, she continued having digestive problems after consuming red meat. A severe episode of diarrhea and vomiting hours after she ate beef prompted her to visit a health care provider 20 days after the tick bite. Blood tests revealed extremely high levels of alpha-gal-specific immunoglobulin E (IgE), confirming alpha-gal syndrome. Her allergy resolved after 10 months.

The second case of alpha-gal syndrome, reported in the same journal issue, involved a 61-year-old wildlife biologist in Washington. After a confirmed bite from the western black-legged tick (I. pacificus), she experienced a skin rash and lip swelling, followed by a severe allergic reaction 29 days later, after she ate red meat, and required emergency epinephrine (EpiPen) treatment. After being diagnosed with alpha-gal syndrome, she avoided meat and had no further reactions. Some years later, she got two more I. pacificus tick bites, which triggered a rise in alpha-gal IgE antibodies.

To date, why tick bites can trigger alpha-gal syndrome is poorly understood. "We are only beginning to delve into the science of this and other tick-borne diseases — there's so much we don't know," Platt said.

Research has shown that some tick species produce alpha-gal antigens — proteins that trigger an immune response — and secrete these antigens in their saliva during feeding. This may trigger the alpha-gal allergy in humans. "The ticks do NOT pick up [alpha-gal antigens] from animals and then transmit them to humans," Platt emphasized.

"More studies are needed to discover details about how a tick bite triggers alpha-gal syndrome in some people, and why bites from lone star ticks appear to cause the majority of the human cases in the United States versus blacklegged, western blacklegged, and other ticks," Salzer said.

Preventing tick bites is the best way to protect against alpha-gal syndrome and other tick-borne diseases, such as Lyme disease and Powassan virus. "When you anticipate being in areas where ticks may live, use an EPA-registered insect repellent and wear permethrin-treated clothing," Salzer advised.

Cats have lived among humans for thousands of years. They probably started hanging around human grain stores, attracted by mice and other vermin, and eventually spread around the world as sailors brought them aboard ships.

Today, cats still help humans control pests, as well as provide companionship. In the past few centuries, humans have bred some cats to display certain traits, like hairlessness, thereby establishing dozens of cat breeds. With their charming mix of aloofness and goofiness, cats continue to amuse and fascinate us.

Everything you need to know about domestic cats

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Where it lives: South, Southeast and East Asia (including India, Sri Lanka, the Philippines, China, Japan and Indonesia)

What it eats: Moths, beetles, flies, crickets and other small insects

Why it's awesome: The Asian hermit spider is no ordinary arachnid. This spider has evolved an adaptation that allows it to reproduce while escaping the threat of female cannibalism: It can detach its penis.

This spider species displays extreme sexual dimorphism, meaning that males and females have significantly different appearances. Females can grow up to around 0.59 inches (15 millimeters), while males are less than 0.20 inches (5 millimeters).

Males face considerable risks during mating due to aggression from females, which may kill and eat their partners before or after mating. Sex can be so treacherous for the males that they have developed the ability to detach their penis so they can leave it pumping sperm while they flee to safety.

In this process of "remote copulation," a male spider's palp — its sperm-delivering organ, of which it has two — can break off inside the female's reproductive tract. The broken-off palp can remain inside the female and continue pumping sperm into her even after the male has escaped.

While studying this "eunuch phenomenon" among orb-web spiders, biologists discovered that the longer the severed palp is left in the female genitals, the more sperm it transfers. And palp breakage induced by the female, instead of the male, led to faster sperm transfer.

The detachable penis also serves another important function: It acts as a mating plug. After breaking off, the embolus — a needle-like structure that delivers the sperm — stays lodged inside the female's reproductive opening to prevent other males from mating with her. This reduces sperm competition and increases the likelihood that the male's genes will be passed on.

After losing its penis, the male spider also becomes more aggressive and guards the female from other males that might try to dislodge the "palp plug" and inseminate the female.

According to a 2011 study in the journal Animal Behaviour, removing one palp reduces the spider's body weight and increases its endurance, thereby boosting its ability to fight. This finding supports what the researchers called a "gloves-off" mating strategy, where the spiders have nothing to live for other than protecting their potential offspring.

The male spiders also have another trick to prevent being eaten by the females: Sometimes, they offer one of their legs to the female as a distraction during mating. This act of self-amputation, known as autotomy, reduces the risk of being attacked or eaten during the mating process. It can also buy the male time to escape.

Cats also like to lick — a lot. And they lick plenty of things that aren't food. When cats lick or suck on an inedible material, it is called "wool sucking." But they don't suck only on wool — they also do it with leather, rubber and plastic.

"Each cat has its own particular predilection," said Dr. Nicholas Dodman, a professor emeritus of animal behavior at Tufts University and a veterinarian who has been studying compulsive behavior in animals for over 30 years.

But why do cats lick plastic bags and other nonedible things? And is it dangerous?

One theory is that this behavior comes from a cat's desire to nurse as a kitten. Siamese cats are the most likely to exhibit wool sucking, and they are also the breed that nurses with their mothers the longest, Dodman said.

"They would like to stay with their mums and cycle a nurse for 12 or 14 weeks," he explained. "And then they're placed at nine weeks. They've still got this suckling drive. And it has to go somewhere." He thinks that drive is what leads cats to suck on wool, leather and plastic.

Related: Why do cats have bald spots in front of their ears?

Other cat breeds nurse for only around seven weeks, so if they leave their mothers at nine weeks, they don't have this suckling desire anymore, he said.

Dr. Valarie Tynes, a veterinarian who specializes in animal behavior, is less certain about Dodson's weaning theory because it hasn't yet been proved experimentally yet. But she agreed that plastic sucking is some kind of self-soothing behavior for the cats, similar to how human babies suck their thumbs.

As far as whether it's dangerous, licking plastic, on its own, doesn't worry Tynes. "If this cat has always licked unusual things ever since it was a young cat and it doesn't do it for an extraordinary part of the day, I worry less about that," she said. "As long as [the cat]'s not eating it."

If a cat is eating plastic or anything else that isn't food, that's called pica, and it's a problem. If the cat ingests nonedible items, they can become lodged in a cat's intestines and require expensive surgeries to be removed. If not treated, these blockages can be fatal.

If your cat eats any nonfood items, you should bring it to the vet, both experts recommended. And if you don't get the treatment you're looking for, consider consulting a behavior specialist, Tynes said.

"The saddest thing for me," she said, "is the clients I've seen who maybe have spent, you know, thousands of dollars on multiple surgeries to remove things from their cat," instead of working to address the problem in the cat's behavior.

When a cat with pica is brought to the vet, first they are tested for any other possible gastrointestinal issues, like parasites. Once the problem is determined to be behavioral, there are a few possible treatments.

Dodman said some vets can prescribe medication similar to human treatments for obsessive-compulsive disorder, like Prozac. Owners can also distract their cats when they are engaging in undesirable behaviors, and provide more toys and other activities for the cats to play with instead. Tynes suggested growing some cat grass or buying a dog chew toy for a cat to eat instead of harmful plastic.

It's also important to remember that your cat doesn't know it's doing anything wrong, Tynes emphasized. Don't blame your feline friend for licking your grocery bag. Just pay attention, and talk to a vet if it becomes a problem.

The fossil, found 250 miles (402 kilometers) north of Cape Town in South Africa, is a new species of multisegmented arthropod that may have lived in oxygen-poor waters, according to the study, published March 26 in the journal Papers in Palaeontology.

Researchers named the new species Keurbos susanae and nicknamed the fossil "Sue" after its discoverer's mom.

"Sue is an inside-out, legless, headless wonder," lead author Sarah Gabbott, a paleontologist at the University of Leicester in the U.K., said in a statement. "Remarkably, her insides are a mineralized time-capsule: muscles, sinews, tendons and even guts all preserved in unimaginable detail. And yet her durable carapace, legs and head are missing — lost to decay over 440 million years ago."

The researchers found the fossils in the Soom Shale, a site known for producing fossils with well-preserved soft tissues, more than 20 years ago. They had hoped to find additional specimens, but fossils of the species turned out to be quite rare. The silt, clay, and mud in which Sue was preserved were deposited on an ancient seafloor, beneath an ocean low in oxygen but high in dissolved, acidic hydrogen sulfide — suggesting that K. susanae may have been adapted for a low-oxygen environment.

Sue dates back to the Late Ordovician mass extinction (443 million years ago), when cold temperatures and glacier advancement eliminated nearly 85% of marine species.

Researchers are still working to understand how soft tissues in fossils like K. susanae are preserved in the Soom Shale. Clay minerals may have played a role, as could calcium phosphate, a compound commonly found in fossilized muscles. On the other hand, the shells and exoskeletons of species preserved in Soom Shale likely dissolved in the acidic ocean.

Because the K. susanae specimen was fossilized inside out, scientists still aren't sure of the species' evolutionary history or how it compares to other fossils from the same time period.

"We are now sure she was a primitive marine arthropod, but her precise evolutionary relationships remain frustratingly elusive," Gabbott said in the statement. The fossil's segmented trunk suggests it had limbs of some kind — but comparing Sue to known fossil species would require a sample with part of the exoskeleton preserved.

Recent quarrying activity has buried the site where Gabbott and her colleagues found Sue, so it's unlikely they'll find other examples of the same species with intact legs or a head, the team said.

"I'd always hoped to find new specimens, but it seems after 25 years of searching this fossil is vanishingly rare — so I can hang on no longer," Gabbott said. "Especially as recently my mum said to me, 'Sarah, if you are going to name this fossil after me, you'd better get on and do it before I am in the ground and fossilized myself'."

Gabbott joked that she named the fossil after her mom because she's a "well-preserved specimen." But the true reason, she said, is that "my mum always said I should follow a career that makes me happy — whatever that may be. For me that is digging rocks, finding fossils and then trying to figure out how they lived what they tell us about ancient life and evolution on Earth."

The scientists also found industrial chemicals in fish and in the ground in the Mariana Trench, meaning human-made pollutants can reach some of the deepest environments on Earth.

Deep-sea fish have developed unique adaptations to survive extreme pressure, low temperatures and almost complete darkness. These species adapt to extreme conditions through unique skeletal structures, altered circadian rhythms and either vision that's extremely fine-tuned for low light, or are reliant on non-visual senses.

In a new study, published March 6 in the journal Cell, researchers analyzed the DNA of 11 fishes, including snailfish, cusk-eels and lizardfish that live in the hadal zone — the region about 19,700 feet (6,000 meters) deep and below — to better understand how they evolved under such extreme conditions.

The researchers used crewed submarines and remotely operated vehicles to collect samples from about 3,900 to 25,300 feet (1,200 to 7,700 m) below the water's surface, in the Mariana Trench in the Pacific and other trenches in the Indian Ocean.

Tracing the evolution of deep-sea fishes, the researchers' analysis revealed that the eight lineages of fish species studied entered the deep-sea environment at different times: The earliest likely entered the deep sea in the early Cretaceous period (about 145 million years ago), while others reached it during the Paleogene (66 million to 23 million years ago), and some species as recently as the Neogene period (23 million to 2.6 million years ago).

Despite different timelines for making the deep sea their home, all the fishes studied living below 9,800 feet (3,000 m) showed the same type of mutation in the Rtf1 gene, which controls how DNA is coded and expressed. This mutation occurred at least nine times across deep-sea fish lineages below 9,800 feet, study author Kun Wang, an ecologist at Northwestern Polytechnical University, told Live Science in an email.

This means all these fishes developed the same mutation separately, as a result of the same deep-sea environment, rather than as the result of a shared evolutionary ancestor — showing just how strongly deep-sea conditions shape these species' biology.

Related: How deep is the Mariana Trench?

"This study shows that deep-sea fishes, despite originating from very different branches of the fish tree of life, have evolved similar genetic adaptations to survive the harsh environment of the deep ocean — cold, dark, and high-pressure," Ricardo Betancur, an ichthyologist at the University of California San Diego who was not involved in the new study, told Live Science in an email.

It's an example of convergent evolution, where unrelated species independently evolve similar traits in response to similar conditions. "It's a powerful reminder that evolution often reuses the same limited set of solutions when faced with similar challenges — in this case, adapting to the extreme conditions of the deep sea," Betancur said.

The expeditions also revealed human-made pollutants in the Mariana Trench and Philippine Trench. Polychlorinated biphenyls (PCBs) — harmful chemicals used in electrical equipment and appliances until they were banned in the 1970s — contaminated the liver tissues of hadal snailfish, the scientists discovered.

High concentrations of PCBs and polybrominated diphenyl ethers (PBDEs), flame retardant chemicals used in consumer products until they fell out of popularity in the early 2000s, were also found in sediment cores extracted from more than 32,800 feet (10,000 m) deep in the Mariana Trench.

Previous research has also found chemical pollutants in the Mariana Trench, as well as microplastics in the deep sea. The new findings further reveal the impacts of human activity even in this ecosystem that's so far removed from human life.

Mariana Trench quiz: How deep is your knowledge?

Sakhawat Ali, a gamekeeper at the Central Karakoram National Park in Gilgit-Baltistan, Pakistan, spotted the elusive animals on March 13 in a remote village called Hushe after two weeks of tracking their pugmarks [pawprints].

"Spotting four snow leopards is a great joy, as it indicates that the snow leopard population is increasing," Ali told Live Science.

Snow leopards (Panthera uncia) are an elusive species of big cat that can be found in mountainous areas across 12 countries in Central and Eastern Asia, and sightings are exceedingly rare. Their white coats render them almost invisible against the snowy mountains they call home, and more than 70% of their habitat remains unexplored, according to the World Wildlife Fund (WWF).

Since late February, Ali said he had been noticing snow leopard pugmarks around the village. "While I was on the roof of my house, I used binoculars to observe the mountains and spotted a female snow leopard along with her four cubs," he said. "I quickly moved closer and filmed them from a distance of about 250 meters [820 feet]."

Related: 50 of the most endangered species on the planet

Snow leopards are usually solo travellers, so seeing four together is exceedingly rare.

"In the village [of Hushe] we are used to seeing snow leopards, but nobody, not even the elders that I spoke to, have ever seen four snow leopards in one go," Ali told CNN.

Female snow leopards typically have between one and five cubs with each litter, according to WWF. At three months old, the cubs begin to follow their mother out of their dens to learn how to hunt in their environment. However, they stay with their mothers until they are almost 2-years-old, according to San Diego Zoo.

The big cats are considered vulnerable to extinction, with only 4,000 to 6,000 individuals left worldwide, according to WWF estimates.

The Baltistan Wildlife Conservation and Development Organization (BWCDO), which shared Ali's video on Facebook, said the sighting was a positive sign of successful conservation efforts in the Hushe Valley area. However, the species still faces numerous threats.

According to the United Nations Environment Program, poaching, habitat fragmentation, prey depletion and climate change all threaten the snow leopard's existence.

These organisms, named Prototaxites, lived around 420 million to 375 million years ago during the Devonian period and resembled branchless, cylindrical tree trunks. These organisms would have been massive, with some species growing up to 26 feet (8 meters) tall and 3 feet (1 meter) wide.

Since the first Prototaxites fossil was discovered in 1843, scientists haven't been sure whether they were a plant, fungus or even a type of algae. However, chemical analyses of Prototaxites fossils in 2007 suggested they were likely a giant ancient fungus.

Now, according to a paper published March 17 on the preprint server bioRxiv, Prototaxites might not have been a humongous fungus after all — rather, it may have been an entirely different and previously unknown life-form. The study has not yet been peer-reviewed.

All life on Earth is classified within three domains — bacteria, archaea and eukarya — with eukarya containing all multicellular organisms within the four kingdoms of fungi, animals, plants and protists. Bacteria and archaea contain only single-celled organisms.

Previous chemical analysis of Prototaxites fossils indicated that they likely fed off decaying organisms, just like many fungi do today, rather than making their food from carbon dioxide in the air like plants.

However, according to this new research, Prototaxites may actually have been part of a totally different kingdom of life, separate from fungi, plants, animals and protists.

The researchers studied the fossilized remains of one Prototaxites species named Prototaxites taiti, found preserved in the Rhynie chert, a sedimentary deposit of exceptionally well-preserved fossils of early land plants and animals in Scotland. This species was much smaller than many other species of Prototaxites, only growing up to a few inches tall, but it is still the largest Prototaxites specimen found in this region.

Upon examining the internal structure of the fossilized Prototaxites, the researchers found that its interior was made up of a series of tubes, similar to those within a fungus. But these tubes branched off and reconnected in ways very unlike those seen in modern fungi.

"We report that Prototaxites taiti was the largest organism in the Rhynie ecosystem and its anatomy was fundamentally distinct from all known extant or extinct fungi," the researchers wrote in the paper. "We therefore conclude that Prototaxites was not a fungus, and instead propose it is best assigned to a now entirely extinct terrestrial lineage."

True fungi from the same period have also been preserved in the Rhynie chert, enabling the researchers to chemically compare them to Prototaxites. In addition to their unique structural characteristics, the team found that the Prototaxites fossils left completely different chemical signatures to the fungi fossils, indicating that the Prototaxites did not contain chitin, a major building block of fungal cell walls and a hallmark of the fungal kingdom. The Prototaxites fossils instead appeared to contain chemicals similar to lignin, which is found in the wood and bark of plants.

"We conclude that the morphology and molecular fingerprint of P. taiti is clearly distinct from that of the fungi and other organism preserved alongside it in the Rhynie chert, and we suggest that it is best considered a member of a previously undescribed, entirely extinct group of eukaryotes," the researchers wrote.

Kevin Boyce, a professor at Stanford University, led the 2007 study that posited Prototaxites is a giant fungus and was not involved in this new research. However, he told the New Scientist that he agreed with the study's findings.

"Given the phylogenetic information we have now, there is no good place to put Prototaxites in the fungal phylogeny," Boyce said. "So maybe it is a fungus, but whether a fungus or something else entirely, it represents a novel experiment with complex multicellularity that is now extinct and does not share a multicellular common ancestor with anything alive today."

More research into Prototaxites fossils needs to be done to determine if they were fungi or a completely different type of life, and what caused them to go extinct millions of years ago.

"The conclusion that it is a completely unknown eukaryote certainly creates an air of mystery and intrigue around it — probably not likely to be solved until more fossils are discovered or new analytical techniques developed," Brett Summerell, a plant pathologist and fungi expert at the Botanic Gardens of Sydney, Australia, who not involved in this new study, told the New Scientist.

One of the things biologists like me do is classify all living things into categories. Insects belong to a phylum called Arthropoda — animals with hard exoskeletons and jointed feet.

All insects are arthropods, but not all arthropods are insects. For instance, spiders, lobsters and millipedes are arthropods, but they're not insects.

Instead, insects are a subgroup within Arthropoda, a class called "Insecta," that is characterized by six legs, two antennae and three body segments — head, abdomen and the thorax, which is the part of the body between the head and abdomen.

Most insects also have wings, although a few, like fleas, don't. All have compound eyes, which means insects see very differently from the way people see. Instead of one lens per eye, they have many: a fly has 5,000 lenses; a dragonfly has 30,000. These types of eyes, though not great for clarity, are excellent at detecting movement.

What is a species?

All insects descend from a common ancestor that lived about about 480 million years ago. For context, that's about 100 million years before any of our vertebrate ancestors — animals with a backbone — ever walked on land.

A species is the most basic unit that biologists use to classify living things. When people use words like "ant" or "fly" or "butterfly" they are referring not to species, but to categories that may contain hundreds, thousands or tens of thousands of species. For example, about 18,000 species of butterfly exist — think monarch, zebra swallowtail or cabbage white.

Basically, species are a group that can interbreed with each other, but not with other groups. One obvious example: bees can't interbreed with ants.

But brown-belted bumblebees and red-belted bumblebees can't interbreed either, so they are different species of bumblebee.

Each species has a unique scientific name — like Bombus griseocollis for the brown-belted bumblebee — so scientists can be sure which species they're talking about.

Related: What is a species?

Quadrillions of ants

Counting the exact number of insect species is probably impossible. Every year, some species go extinct, while some evolve anew. Even if we could magically freeze time and survey the entire Earth all at once, experts would disagree on the distinctiveness or identity of some species. So instead of counting, researchers use statistical analysis to make an estimate.

One scientist did just that. He published his answer in a 2018 research paper. His calculations showed there are approximately 5.5 million insect species, with the correct number almost certainly between 2.6 and 7.2 million.

Beetles alone account for almost one-third of the number, about 1.5 million species. By comparison, there are "only" an estimated 22,000 species of ants. This and other studies have also estimated about 3,500 species of mosquitoes, 120,000 species of flies and 30,000 species of grasshoppers and crickets.

The estimate of 5.5 million species of insects is interesting. What's even more remarkable is that because scientists have found only about 1 million species, that means more than 4.5 million species are still waiting for someone to discover them. In other words, over 80% of the Earth's insect biodiversity is still unknown.

Add up the total population and biomass of the insects, and the numbers are even more staggering. The 22,000 species of ants comprise about 20,000,000,000,000,000 individuals — that's 20 quadrillion ants. And if a typical ant weighs about 0.0001 ounces (3 milligrams) — or one ten-thousandth of an ounce — that means all the ants on Earth together weigh more than 132 billion pounds (about 60 billion kilograms).

That's the equivalent of about 7 million school buses, 600 aircraft carriers or about 20% of the weight of all humans on Earth combined.

Many insect species are going extinct

All of this has potentially huge implications for our own human species. Insects affect us in countless ways. People depend on them for crop pollination, industrial products and medicine. Other insects can harm us by transmitting disease or eating our crops.

Most insects have little to no direct impact on people, but they are integral parts of their ecosystems. This is why entomologists — bug scientists — say we should leave insects alone as much as possible. Most of them are harmless to people, and they are critical to the environment.

It is sobering to note that although millions of undiscovered insect species may be out there, many will go extinct before people have a chance to discover them. Largely due to human activity, a significant proportion of Earth's biodiversity — including insects — may ultimately be forever lost.

Curious Kids is a series for children of all ages. If you have a question you’d like an expert to answer, send it to CuriousKidsUS@theconversation.com.

This edited article is republished from The Conversation under a Creative Commons license. Read the original article.

Sharks have long been thought to be mute, relying on stealth to hunt their prey and avoid predators. But now, sharks have been recorded making sounds for the very first time.

The new recordings reveal that rig sharks (Mustelus lenticulatus) — small, bottom-dwelling sharks native to New Zealand — emit distinct clicks when handled by researchers underwater. These sounds were consistent and repeated across multiple individuals, and were potentially tied to distress or defensive responses, according to a study published Wednesday (Mar. 26) in the journal Royal Society Open Science.

The recordings represent the first known case of a shark actively producing sound. "Sharks have sensory systems that are more refined than their hearing, like their electroreceptors, their smell and the way they propel themselves through the water," study lead author Carolin Nieder, a researcher at the Woods Hole Oceanographic Institution, told Live Science. "But I think the original notion that we had that sound isn't important at all is also likely not true."

Ten juvenile rig sharks were observed making sounds by accident during routine behavioral experiments at the University of Auckland's Leigh Marine Laboratory. When briefly handled by researchers underwater, all 10 sharks produced audible clicks.

Related: Octopus spotted riding on top of world's fastest shark

These clicking sounds were very frequent during the first few handlings but then stopped as the experiments progressed, Nieder said. "Maybe they weren't afraid for their lives anymore," she said, adding that in the wild, loud clicks may serve as a split-second distraction for juvenile sharks to make their escape when they are seized by predators.

Most sharks are thought to be silent because they lack swim bladders — air-filled sacs commonly used by fish to make sounds. MicroCT scans and 3D reconstructions of rig sharks also revealed no obvious sound-producing organs or structures.

The team proposed that the sounds could be coming from the sharks snapping their teeth.

Rig sharks have broad, blunt teeth arranged in tightly packed, plate-like formations, which are ideal for crushing hard-shelled prey like crabs. This "pavement dentition," may also serve a second function of producing noise when the jaws snap shut, the researchers said.

However, Nieder noted that without direct observation of the sharks' jaws during click production, the mechanism remains speculative.

Each click lasted around 48 milliseconds, with volumes sometimes exceeding 155 decibels, which is comparable to shotgun blast.

Roughly three-quarters of the clicks were single bursts, while the rest were short double-clicks. The scientists observed that about 70% of these clicks were accompanied by calm, swaying body movements, but a few occurred without any visible motion at all.

Whether the clicking is an accidental byproduct of handling or a purposeful behavior remains unknown.

The sharks' own hearing range is largely below 1 kilohertz, far lower than the frequencies of its clicks, meaning it's unlikely the clicks are meant for communicating with other sharks.

However, some known predators of rig sharks, such as New Zealand fur seals (Arctocephalus forsteri), are sensitive to higher frequencies and might be startled or confused by the sharp clicks.

Several species of rays and skates — close relatives of sharks — are also known to produce clicks when disturbed by divers. These sounds are thought to serve as warning signals or distress calls.

Nieder said future studies could target closely related shark species to investigate whether they are also capable of making noises, and whether they make noise in response to stress.

Adrian Gutteridge, a shark biologist with the IUCN Shark Specialist Group who was not involved in the study, said more research will be needed to establish what the shark clicks are for, and what they could mean.

"It's too early to tell whether it's a response, kind of saying, 'go away,' or if [it's] just their nervous system is firing off which just happens to make their teeth and jaws click," he told Live Science.

Shark quiz: How much do you know about these iconic ocean superstars?

This new genus and species is a therizinosaur, plant-eating, two-legged giants with long claws, and was discovered buried in the Gobi Desert, according to a new study published Tuesday (March 25) in the journal iScience.

Unlike other therizinosaurs, which have three fingers on their hands equipped with long, sharp claws, this new species only has two fingers. This unique anatomy inspired its scientific name, named Duonychus tsogtbaatari, which is Greek for "two digits" and honors the Mongolian paleontologist Khishigjav Tsogtbaatar.

"Many species of therizinosaurs have been discovered, and this group had pretty much been defined by their three-fingered hands sporting large claws," study co-author Darla Zelenitsky, a paleontologist at the University of Calgary in Canada, told Live Science in an email. "To find a specimen with only two fingers/claws was surprising as this was so out of the ordinary for this group of dinosaurs."

Related: 166 million-year-old fossil found on Isle of Skye belongs to pony-size dinosaur from Jurassic

Therizinosaurs are a group of dinosaurs that lived across what is now Asia and North America during the Late Cretaceous Period (100 million to 66 million years ago). Despite being part of the theropod group of dinosaurs — typically associated with carnivorous dinosaurs like Tyrannosaurus rex — therizinosaurs were herbivorous. These dinosaurs are known for their enormous, sickle-shaped claws, with some species growing talons as long as 20 inches (50 centimeters).

All other therizinosaurs that have previously been discovered, including Therizinosaurus and Beipiaosaurus, have three clawed fingers on their hands, making the discovery of two-clawed D. tsogtbaatari unusual.

"Therizinosaurs are already some of the most unusual dinosaurs out there, but Duonychus tsogtbaatari takes it to another level," study lead author Yoshitsugu Kobayashi, a paleontologist at Hokkaido University in Japan, told Live Science in an email. "This newly discovered species from Mongolia breaks the mold with just two fingers instead of the typical three, offering a rare glimpse into how theropod hands evolved and adapted." "But what truly makes this discovery exciting is the incredibly well-preserved keratinous sheath on its claw — the first such case in a medium- to large-sized theropod dinosaur," Kobayashi added.

The new fossil was unearthed during the construction of a water pipeline in the Bayanshiree Formation in Ömnögovi Province, southern Mongolia. The specimen had excellently preserved hands, with a 3D sheath where the claw — made out of keratin, like our fingernails — would have been. Parts of the arms, spine and hips were also preserved.

"The hands, a hallmark of therizinosaurs, are exquisitely preserved with all the finger and wrist bones intact in this specimen," Zelenitsky said. "Even the keratinous sheath of the claw is preserved revealing how big and sharp its claws really were."

Other species of dinosaur, such as T. rex, had two fingers, but this marks the first time a therizinosaur has been found with fewer than three digits. This species likely evolved to lose one of the three fingers of its ancestors, the study authors suggested.

The researchers think that D. tsogtbaatari may have evolved this unique hand in order to better grip vegetation, allowing for more efficient feeding.

"The loss of the third finger in Duonychus tsogtbaatari might actually have made its remaining two fingers even better at what they were designed for — grasping," Kobayashi said. "Based on the shape of its well-preserved claw and how it curved, Duonychus was likely using its hands to grab onto branches and pull vegetation closer, kind of like how chameleons do today." "We think many therizinosaurs may have used their hands for foraging in a 'hook-and-pull' motion, but Duonychus takes this to another level with its extreme claw structure."

Additionally, Kobayashi suggested that the claws may have played other roles, such as in "defense, courtship, or even play."

The researchers are thrilled by this discovery, as it not only reveals unexpected diversity within therizinosaurs, but also marks the fifth time that a theropod dinosaur group has evolved to lose their third finger.

"While more fossils would help confirm this, all signs point to Duonychus representing a true evolutionary shift, not just a fluke," Kobayashi said. "It’s a remarkable find that reshapes our understanding of therizinosaurs and theropod evolution as a whole."

The mammoths were discovered during an excavation of the Langmannersdorf site, about 40 miles (65 kilometers) west of Vienna; the bones and tusks were clustered in two distinct zones about 49 feet (15 meters) apart, researchers said in a statement.

In one of the two zones, the research team found the mammoth bones of several individuals piled up together, many of which had marks and scars from human tools — a sign they had been butchered — as well as stone tools scattered nearby.

In the second zone, the team unearthed the remains of at least three separate mammoths. They found the fragmented and whole remains of the mammoth's enormous tusks clustered together, separate from the bones, which shows Paleolithic humans were likely processing the mammoths' ivory. This ivory could have been used to make spearheads, the archaeologists suggested.

"The fact that we found not just individual bones here, but intensively used areas in which several animals were processed, has more than exceeded our expectations," Marc Händel, an archaeologist at the Austrian Archaeological Institute of the Austrian Academy of Sciences (ÖAW), said in a statement. Previous evidence has shown that ancient humans used mammoth ivory to craft tools, such as implements to make ropes, ornaments, accessories and spears and arrowheads for hunting.

Woolly mammoths (Mammuthus primigenius) were large, elephant-like mammals that measured about 11 feet tall (3.5 meters) and had huge, curved tusks. They roamed across North America, Europe and Asia during the last ice age, which ended around 11,700 years ago.

These enormous animals were a crucial resource for Paleolithic hunter-gatherers; they provided food, bones for tools and shelter, and hides for warmth. Most went extinct around 10,000 years ago, likely due to climate change and human hunting, but small populations survived on isolated islands until about 4,000 years ago.

Related: 200000-year-old 'mammoth graveyard' found in UK

The Langmannersdorf site was first excavated between 1904 and 1907, and evidence of two mammoth hunter camps was unearthed in 1919 and 1920. In the years since, researchers from across Europe have worked at the site to discover more relics, in hopes of better understanding the relationship between ancient humans and woolly mammoths.

Around 25,000 years ago, just before the peak of the last ice age about 20,000 years ago, herds of mammoths are thought to have used the Perschling Valley in Austria as a migration route, where they grazed on grasses and shrubs as they traveled. The discovery of the mammoth processing site in Langmannersdorf indicates that ancient humans understood the annual movement of the mammoths and hunted them specifically when they were passing through the valley, the researchers said.

This discovery therefore gives researchers important insight into the hunting culture of humans during the last ice age.

Researchers at the ÖAW will study the mammoth bones and tusks, as well as the stone tools, to determine more details about the lives of these ancient creatures and the humans who hunted them. The remains will then be stored at the Natural History Museum in Vienna, and others will be displayed at the Perschlingtaler Heimatmuseum (Perschling Valley Local History Museum).

The fossils of the new species, named Ferruaspis brocksi, were unearthed by paleontologists at the McGraths Flat fossil site in New South Wales, Australia, according to a new study published March 17 in the Journal of Vertebrate Paleontology.

Inside several of the fish's stomachs were the fossilized remains of their last suppers, including bits of insect larvae, two insect wings, and a bivalve (a mollusk with two hinged shells, such as a clam or a mussel).

The discovery is the first fossil of a freshwater smelt — a small, silvery fish — in the group Osmeriformes to have been discovered in Australia and will help scientists determine when these fish arrived on the enormous island.

"The discovery of the 15 million-year-old freshwater fish fossil offers us an unprecedented opportunity to understand Australia's ancient ecosystems and the evolution of its fish species, specifically the Osmeriformes group during the Miocene epoch, 11-15 million years ago," study lead author Matthew McCurry, a paleontologist at the Australian Museum and the University of New South Wales, said in a statement.

Osmeriformes is a broad order of fish that includes various smelt species found worldwide, both in freshwater and marine environments. Smelt are relatively common across the U.S., particularly in the Great Lakes, the Northeast, the Pacific Northwest, and Alaska, though some species are also present in inland rivers and lakes. There are at least six species of smelt across the country, including rainbow smelt (Osmerus mordax), Eulachon or Columbia River smelt (Thaleichthys pacificus) and delta smelt (Hypomesus transpacificus).

Scientists have long wondered exactly when smelt and related species arrived in Australia because the fossil record for this group of fish and their ancestors has been notably sparse. "Without fossils it has been hard for us to tell exactly when the group arrived in Australia and whether they changed at all through time," McCurry said.

Related: Living fossils: 12 creatures that look the same now as they did millions of years ago

In the new study, the researchers describe how they discovered the fossilized remains of F. brocksi embedded in goethite, an iron-rich mineral. By analyzing the fossils with high-powered microscopes, the researchers discovered that the specimens had been preserved with a surprisingly high level of detail. The position of the fish's bones and fins, cells that gave the fish color, and their final meals had all remained frozen in time for 15 million years.

Because the paleontologists discovered several fish from this new species preserved at the same site, they could piece together what the ancient fish species might have looked like, as not every fish was entirely preserved. According to the researchers, F. brocksi represents an early ancestor of species in the Osmeriformes order found across Australia and New Zealand today.

"The fossils formed between 11 [million] and 16 million years ago and provide a window into the past," McCurry said. "They prove that the area was once a temperate wet rainforest and that life was rich and abundant in the Central Tablelands, NSW [New South Wales]."

Their stomach contents also offer a glimpse into the behavior of this ancient species. "We now know that they fed on a range of invertebrates, but the most common prey was small phantom midge larvae," McCurry said.

Additionally, the unexpected discovery of fossilized pigment cells called melanophores allowed the researchers to determine what color the fish might have been. "The fish was darker on its dorsal surface, lighter in colour on its belly and had two lateral stripes running along its side," study co-author Michael Frese, a researcher at the University of Canberra and Australia's national science agency CSIRO, said in the statement.

Melanophores are responsible for producing melanin, the pigment that gives color to skin, hair, eyes and feathers.

"Fossilised melanosomes have previously enabled palaeontologists to reconstruct the colour of feathers," Frese said, but melanosomes have never been used to reconstruct the color pattern of a long-extinct fish species.

But when an independent team investigated Clever Hans, they concluded his act was a fraud. It turned out that the horse actually just responded to subconscious body-language cues from his trainer and couldn't really comprehend human language or perform arithmetic feats.

Today, researchers are still testing the limits of animals' ability to understand humans, but examples like Clever Hans show just how difficult that task can be. So do we know if any animals can actually understand human language?

Animal language studies with primates, birds, dolphins, and other animals flourished through the 1960s and 1970s, but skeptics went on to criticize this research, saying the animals were only mimicking their trainers like Clever Hans. Though many animals are adept at picking up on context clues like body language and tone of voice, it's less clear if they understand the meaning of words or more complex features of language like grammar. But today, research is beginning to suggest that, with training, some animals may understand certain features of human language, such as the sound and meaning of specific words.

"Humans are special in many ways, and certainly language is unique to humans," Simon W. Townsend, a professor of evolutionary anthropology at the University of Zurich, told Live Science. "But I think more and more, we're finding that there are really quite some similarities between the communication systems of animals and humans."

Related: Can animals learn another species' 'language?'

Can primates learn human language?

One of the most famous animal language experiments involves Koko, a female western lowland gorilla who learned modified American Sign Language (ASL). Koko, who died in 2018, could use about 1,000 signs and respond to over 2,000 words in spoken English.

However, experts warned that there's a big difference between learning some modified signs and actually mastering ASL, and Koko was never anywhere near fluent in sign language. Critics also pointed out that Koko sometimes signed nonsensically, and her trainers tended to lean on their own interpretations to make sense of Koko's signs.

According to comparative psychologist and linguist Michael Tomasello, the title for most advanced language skills in a primate goes to Kanzi, a male bonobo (Pan paniscus) who lived from 1980 to 2025. Kanzi communicated through a lexigram board, a keyboard of about 200 arbitrary symbols that corresponded to things in his environment.

Townsend, who worked with Kanzi, says the bonobo understood the symbols on his lexigram board well and could use them to communicate with his trainers. Kanzi used symbols for people's names, common objects, actions and locations, and he had vocalizations for "yes" and "no." He used his lexigram board to ask for objects or request certain actions.

"He's learned symbolic communication, which is a feature of another species' communication system," Townsend said. But, Townsend added, human language is more than just using symbols; it also involves combining those symbols into larger structures to create more complex meaning — a feature of language called syntax. If Kanzi grasped syntax, that would indicate a deeper understanding of our communication systems.

So far, studies have shown that Kanzi could order symbols at a rate better than random chance, but some critics doubt the bonobo's grammatical abilities. Townsend and other researchers studied Kanzi up until his death to learn the limits of his abilities to combine symbols. Their research is currently unpublished.

Kanzi understood some spoken English, too. In a 1993 study, researchers found that when the bonobo listened to brand-new sentences, like "Put on the monster mask and scare Linda," he could complete the requested task about three out of four times, outperforming a 2.5-year-old child.

Can dogs understand humans?

Most animals have no hardwired evolutionary reason to care about human language. But dogs, who've lived alongside humans for at least 14,000 years, have a special motivation to listen to their owners and respond appropriately.

Dogs are highly tuned in to the specific sounds and tones of voice that humans use to communicate. In fact, dogs show interest in human voices and gestures as early as 8 weeks old. Dogs are so used to human voices that they can tell when speech has been scrambled, and neuroscience research even suggests that dogs have their own mental representations of words, suggesting a deeper comprehension of language similar to humans'.

Related: Are dogs smarter than wolves?

Some prodigious dogs may even grasp basic grammar. One of them was Chaser, a highly trained border collie, known as the "smartest dog in the world," who learned over 1,000 words. According to a 2011 study, she could differentiate commands such as "bring the sock to the ball" and "bring the ball to the sock," indicating a basic understanding of syntax.

Federico Rossano, an associate professor of cognitive science at the University of California, San Diego, is using button boards — a series of buttons that play a recorded word when pressed — to investigate the linguistic capabilities of our canine companions.

In 2024, Rossano showed that dogs respond to the actual sounds of words and not just to their context, like their owner putting on their shoes while saying it's time to go outside. In a study of 59 dogs, the canines listened as a researcher pressed buttons with words related to "outside," "play" and "food," as well as a nonsensical word to serve as a comparison. The researcher wore headphones so their reactions and body language didn't affect the dogs' responses.

Even without these context clues, the team found that when dogs heard the recordings relating "outside" and "play," they tended to start exhibiting behaviors related to going outside or playing, respectively, such as running to the door or grabbing a toy.

The research is a promising step toward showing that dogs can understand human speech even without the context clues that come along with it. But other studies have found that dogs can't differentiate between words that differ by a single sound, such as "sit" and "set," so there may be a limit to how much they can understand.

Rossano emphasized that his studies are not meant to prove that dogs can "talk." Some Instagram-famous pets have gone viral for seemingly advanced communication through button boards, but these cases aren't the focus of his studies. For now, Rossano is focused on investigating the basics.

Like other animal language researchers, Rossano still has a lot of questions. He's currently investigating whether dogs use buttons to refer to people or objects that aren't currently present, and whether they combine buttons to refer to things they don't know the names of. Both of these feats would imply more complex cognitive processes.

Federico admits he began the research with some skepticism, but his view of dogs' language capabilities has "100%" changed since then.

"Maybe there's more of a mind there than we give them credit for," he said.

Animal quiz: Test yourself on these fun animal trivia questions

Where it lives: Central and South America

What it eats: Large insects, bats and small birds

Why it's awesome: The great potoo is a master of disguise. Its mottled gray-brown feathers and ability to remain perfectly still often cause it to be mistaken for a tree branch or stump, helping it evade detection by predators.

Native to the forests and tropical lowlands of Central and South America, this nocturnal bird can grow to 24 inches (60 centimeters) tall and has a wingspan of more than 28 inches (70 cm). Its gray, brown and white plumage helps it blend seamlessly with the bark of the trees it lands on, making it nearly undetectable by other animals.

By day, great potoos remain silent and still in the trees. But at night, they become active hunters. Their large, owl-like eyes, which protrude from the sides of their heads, provide excellent vision in low-light conditions. Equipped with a large, flattened beak and mouth, these birds are well-adapted to snatching prey such as flying insects and bats out of the air.

Great potoos also have slits in their eyelids, which enable them to see when their eyes are closed. These "notches" help the birds to sense light and movement through their shut eyelids, so they can detect predators and prey even when resting.

Great potoos are also unusual thanks to their distinctive calls. Throughout the night, they emit a loud, moaning growl. This ghostly call has earned the bird a mythical status in local folklore, with some communities in South America believing the sounds to be children calling for lost parents. These calls are used for communication and to defend their territories.

Potoos are monogamous birds, forming lifelong pairs that share the responsibilities of incubation and care for their young. Female great potoos lay a single egg in a natural depression on a tree branch, so they rely on their camouflage and sight to protect themselves and their offspring.

The incubation period for great potoo eggs is approximately 30 days, with both parents sharing the responsibility of incubating the egg. Due to their elusive nature, not much is known about their lifespan — but they are believed to live for around 12 to 14 years, like other bird species.

But why did they give up flight? Why don't all birds fly?

The ability to fly is especially useful for escaping predators and traveling long distances in search of food and favorable living conditions. However, flight requires a lot of energy; birds burn about 75% more energy per day than similarly sized mammals do.

"If flight isn't necessary, birds can better survive and reproduce if they divert that energetic investment elsewhere," Natalie Wright, an associate professor of biology at Kenyon College in Ohio, told Live Science in an email.

In a 2016 paper published in the journal PNAS, Wright and her colleagues noted that island-dwelling birds, facing few to no predators and less competition for food and habitat, tend to evolve toward flightlessness.

"When living on an island without predators and without the need to migrate or travel long distances, for many kinds of birds the costs of flight outweigh the benefits," Wright said.

Related: Why do parrots live so long?

The shift to flightlessness leads to physical changes in birds. Over evolutionary time, their pectoral flight muscles shrink. The sternum (breastbone) with its central ridge (keel) — where flight muscles attach — also becomes smaller, Wright said. Wing bones — the humerus, ulna and carpometacarpus — become shorter and less robust, while their legs grow longer and sturdier as an adaptation to a more terrestrial lifestyle, she added.

Some birds have traded flight for superior swimming abilities. Penguins, for instance, retained their flight muscles and keel but repurposed them for swimming. "They use their wings to fly underwater," Peter Ryan, a professor emeritus of ornithology at the University of Cape Town in South Africa, told Live Science in an email. The flightless auk (Pinguinus impennis) also uses its wings to propel itself through water.

In birds that have been flightless for a long time, the long, stiff feathers needed for flight (flight feathers) disappear too, Ryan said. In some species, like kiwis and the Inaccessible Island rail (Atlantisia rogersi), the body feathers lose barbules — the tiny, hook-like structures that normally keep them aerodynamic — giving them a fluffier, fur-like appearance, Ryan added.

A 2025 study published in the journal Evolution found that flightless birds lose feather features in the reverse order of how they first evolved. The research also concluded that skeletal changes occur before changes in plumage, as it takes significantly more energy to grow and maintain bones than it does to maintain feathers.

Although flightless birds are uncommon today, fossils reveal that they were far more prevalent and diverse a few thousand years ago, Tim Blackburn, a professor of invasion biology at University College London, told Live Science in an email. However, the arrival of humans and animals like rats and dogs exposed these birds to predators.

"Having sacrificed their capacity to take to the air, there was no time for them to re-evolve this useful ability," Blackburn said. This led to the rapid extinction of iconic birds like the dodo (Raphus cucullatus) on Mauritius, the moa in New Zealand, and many others.

A 2020 study co-authored by Blackburn and published in the journal Science Advances found that there would be four times as many flightless bird species on Earth today were it not for human-driven extinctions.

The loss of flight happened at least 150 times in different groups of birds throughout evolutionary history, Ferran Sayol, first author of the study and a researcher at Centre for Ecological Research and Forestry Applications (CREAF) in Barcelona, Spain, told Live Science in an email.

"Many of these species thrived on islands without predators but disappeared shortly after when humans arrived (due to direct hunting or introduced predators), making flightlessness seem rarer than it actually was," Sayol said.

Herds of wild bison (Bison bison) have meandered through Yellowstone's vibrant landscape since prehistoric times. Grazing freely in the expansive grasslands of the park, these are the last free-range bison in the United States.

Although these animals are now abundant in the national park, poaching pushed the local population near extinction by the turn of the 20th century. Park managers tried several methods to help conserve Yellowstone’s bison, halting poaching and even introducing a new herd to the region.

Thanks to conservation efforts, both the native herd and the introduced herd, which consisted of adults from Montana and Texas and calves from Yellowstone’s native herd, were able to thrive. Later genetic analyses showed that descendants of this introduced group remained genetically distinct from the native bison — until now.

In the past 20 years, Yellowstone's two bison subpopulations have become one large interbreeding herd, according to the new genetic study, published Sept. 13, 2024 in the Journal of Heredity.

"I think the kinds of questions that we ask about this population at Yellowstone can only be answered using genetic technology," study senior author Jim Derr, a professor at Texas A&M's College of Veterinary Medicine and Biomedical Sciences, told Live Science. "No observational information is going to help you because you don't know who's breeding with who."

To reveal the breeding dynamics of the droves of bison in Yellowstone, workers at the National Park Service (NPS) collected tissue samples biopsied from 282 individuals for analysis.

Closely analyzing the bison's genetic markers gave the researchers clues into their lineage and how the population has changed over time.

Comparing the genetic markers they found in Yellowstone's current bison population to those from samples taken in the early 2000s, the researchers concluded that the two groups roaming the land interbred frequently enough that they are no longer genetically distinct.

The exact cause of the change isn't clear, but the researchers say it was likely a gradual shift in behavior over the past 20 or more years. "Part of it is just the bison exploring different areas and figuring their way out and running into each other," study lead author Sam Stroupe, a postdoctoral research associate at Texas A&M University, told Live Science.

The researchers hope this new analysis will help with ongoing efforts to conserve and manage the herd at Yellowstone.

Staff at the national park have been managing the bison population as two groups since individuals were first brought in from out-of-state in 1907. Having only one herd to look after could make conservation and management of the species easier, the researchers said.

"I think everyone wants bison in Yellowstone National Park to be managed appropriately and to have good stewardship of that herd," Derr said. "Hopefully we can give them a little bit of insight with this genetic information."

An octopus has been spotted catching a ride from an unlikely marine friend: a superfast shark.

Researchers captured a video showing the orange-hued octopus clinging to the back of a large shortfin mako shark (Isurus oxyrinchus) as it swims.

This "sharktopus" was spotted in the Hauraki Gulf off the northern coast of New Zealand's North Island during a December 2023 research trip.

"A large metallic grey dorsal fin signalled a big shark, a short-fin mako. But wait, what was that orange patch on its head? A buoy? An injury?" Rochelle Constantine, a marine biology professor at the University of Auckland who was on the research trip, wrote in a statement. "We launched the drone, put the GoPro in the water and saw something unforgettable: an octopus perched atop the shark's head, clinging on with its tentacles."

The researchers were bemused by this bizarre sight, as octopuses usually live on the ocean floor, while shortfin makos spend most of their time swimming near the surface.

"We really don't know how this octopus, that lives on the seabed, came across this 3 m [meters, or 10 feet] mako shark that lives in pelagic — open ocean waters. It really is a mystery — but the ocean is filled with unexpected things," Constantine told Live Science in an email.

Related: Searching for 'Makozilla' — the supersized mako sharks in the North Pacific

Shortfin mako sharks are the fastest shark species in the world, reaching top speeds of up to 46 mph (74 km/h). They can grow as long as 12 feet (3.7 m) and weigh as much as 1,200 pounds (545 kilograms). These sharks are known for their incredible jumping ability, being able to leap up to 20 feet (6 m) out of the water. They usually hunt near the ocean surface but have been spotted as deep as 1,640 feet (500 m). Their diet mostly consists of other fast-swimming fish such as swordfish and tuna, as well as squid and occasionally other sharks.

The researchers watched the strange "sharktopus" for 10 minutes before leaving the odd companions to continue their journey.

"The shark may not be bothered by the octopus — it certainly didn't appear to be bothered as it swam along slowly," Constantine said. "The octopus was keeping all of its tentacles together on the shark's head, perhaps to avoid being seen but it could stay there while the shark was swimming slowly. I suspect the octopus would have dislodged if the shark swam faster."

Shortfin mako sharks are listed as endangered on the IUCN Red List, largely due to their fins being highly prized in the shark fin trade. They also get caught accidentally as bycatch in tuna and swordfish fisheries, especially with longline fishing gear. Their slow rate of reproduction means that they can't reproduce fast enough to keep up with fishing pressure, leading to population declines.

"One of the best things about being a marine scientist is that you never know what you might see next in the sea. By supporting conservation initiatives, we can help to ensure that such extraordinary moments keep happening," Constantine said in the statement.

Shark quiz: How much do you know about these iconic ocean superstars?

In a new study, researchers inhibited a gene during embryonic development to make chicken feathers more primitive, like the kind of simple tube-shaped proto-feathers that likely first emerged in the ancestors of dinosaurs in the Early Triassic 250 million years ago.

They succeeded — but only temporarily. The chickens showed delayed feather development and naked spots at hatching, but within a few weeks, their plumage looked like any other fowl's.

The study is part of a broader effort to learn how and why feathers first evolved. Researchers had previously altered the same gene to turn scaly chicken feet feathery, but turning back the clock on feather evolution proved harder.

"Our experiments show that while a transient disturbance in the development of foot scales can permanently turn them into feathers, it is much harder to permanently disrupt feather development itself," study senior author Michel Milinkovitch, a professor of genetics and evolution at the University of Geneva, said in a statement. "Clearly, over the course of evolution, the network of interacting genes has become extremely robust, ensuring the proper development of feathers even under substantial genetic or environmental perturbations."

Related: Dark regions of the genome may drive the evolution of new species

Just because the researchers didn't make permanently dino-feathered chickens, it doesn't mean the study was a failure. Milinkovitch and his co-author Rory Cooper, now a research fellow at the University of Sheffield in the U.K., showed how a particular gene, the whimsically named "Sonic Hedgehog" gene, is important in feather evolution. By disturbing this gene, the researchers were able to temporarily disrupt feather formation.

The first feathers were not the complicated, branching features seen on birds today. They were single tubules, shaped like tiny drinking straws. To find out how evolution built everything from soft down to gaudy peacock feathers from these simple tubes, Milinkovitch and Cooper first used a technique called light sheet fluorescence microscopy to examine chicken feather development in the egg. This method uses lasers to image thin slices of a sample.

Feathers start to develop in embryonic chickens nine days after the egg is laid. First, thick spots called placodes pop up all over the developing chicken, the researchers observed. Next, these placodes grow feather buds, which gradually develop into the familiar branching feather form with the help of keratin, the same protein found in human hair and fingernails. The Sonic Hedgehog gene, which is well known to guide embryonic development in animal species, plays a role in all of these steps.

Next, the researchers injected an inhibitor of the Sonic Hedgehog gene into eggs on the ninth day of development to see what would happen. Within days, feather bud growth was stunted. The inhibitor also reduced the complex branching pattern that develops as feathers mature on the embryo.

By day 17 of development, however, the feather growth had partially recovered as the inhibition of the Sonic Hedgehog gene wore off. Chickens that were allowed to hatch had patchy feathers, with some naked spots and other places where soft, down-like feathers had formed, but they did not have outer feathers with a central "rachis," the distinctive quill structure in feathers. By the 49th day of life, however, these chickens molted, and the new feathers that came in developed normally.

The studies show that the Sonic Hedgehog gene has been involved both in the evolution of proto-feathers into today's feathers, as well as in the diversification of feathers into different shapes and sizes across species, the researchers reported March 19 in the journal PLOS Biology.

"The big challenge now," Milinkovitch said, "is to understand how these genetic interactions have changed to allow for the emergence of protofeathers early in the evolution of dinosaurs."

As an infant, Kanzi, who was born at the Emory National Primate Research Center in Atlanta, Georgia, accompanied his adoptive mother Matata to language lessons. But while Matata was not interested in learning from her human caretakers, Kanzi surprised them by quickly learning the lexigrams, or symbols that map to words, that the researchers were trying to teach his mother, in much the same way human children learn language by listening to their parents talking.

Primatologists have used lexigrams since the 1970s to understand how chimpanzees and bonobos think and communicate. Using a special lexigram keyboard, the great apes are encouraged to communicate with their caretakers by pressing different buttons or pointing to pictures.

Researchers taught Kanzi more than 300 lexigrams, and Kanzi combined them to create new meanings, an important aspect of symbolic thinking — something which experts previously assumed only humans were capable of.

But Kanzi was also able to understand and respond to requests in spoken English. In a study undertaken when Kanzi was 8 years old, he and a 2-year-old human child were given 660 spoken instructions. Kanzi outperformed the child, suggesting his linguistic ability was at least as good as a human toddler's.

Related: Chimps learned tool use long ago without human help

In another study, Kanzi learned some American Sign Language (ASL) simply by watching videos of Koko the gorilla, who had previously been taught to use ASL. And when separated by a wall from his sister, Panbanisha, Kanzi vocalized a sound for 'yogurt' that Panbanisha understood.

Although Kanzi showed one-of-a-kind linguistic abilities for an ape, he didn't speak in the same way humans do. Researchers think this is related to the anatomical differences between chimpanzee and human vocal tracts. However, a 2024 study published in Scientific Reports suggests that chimpanzee vocalization abilities may have been underestimated, as these apes can produce novel sounds and have the brain capacity necessary for speech.

Beyond his language skills, Kanzi showed off his ability to make and use stone tools, earning him the epithet "bonobo genius." He was then taught to build a fire and cook food, demonstrating his ability to learn behaviors key to human evolution.

Later in life, Kanzi was even taught to play video games. He seemed to understand how to beat the arcade game Pac-Man and defeated the final boss of Minecraft.

On March 18, staff at the Ape Initiative found Kanzi unresponsive. He was being treated for heart disease, according to the statement, but necropsy results clarifying his cause of death are pending.

Evolution quiz: Can you naturally select the correct answers?

Sea spiders, also known as pycnogonids, are distant cousins of the creepy-crawly arachnids we see scuttling about on land. These creatures can have leg spans of up to 20 inches (51 centimeters) — nearly double those of the largest land spiders, whose leg spans top out at around 12 inches (30 cm).

According to the Schmidt Ocean Institute, which shared the footage, the spider's massive size is a result of deep-sea gigantism, the tendency for deep-sea creatures to grow significantly larger than their shallow-water relatives. In this case, the pycnogonid was filmed at a depth of 6,903 feet (2,104 meters).

Related: 32 truly bizarre deep-sea creatures

"Immense pressure and frigid temperatures, while insurmountable obstacles to land-lovers like humans, allow some animals to have very slow metabolisms and the ability to reach gargantuan proportions," Schmidt Ocean Institute representatives wrote in a Facebook post.

Larger animals can also move faster and farther to find food or to locate a mate, which is important when both are scarce.

Deep-sea gigantism is particularly prevalent toward the poles, where freezing temperatures facilitate slower metabolisms. Schmidt Ocean Institute representatives described sea spiders as both "abundant" and "abundantly large" in polar regions.

There are roughly 1,500 species of sea spider known to science and likely many more yet to be discovered, according to the post. Sea spiders inhabit oceans around the world and range just a few millimeters to the size of a serving platter. The species of spider in the video from the Schmidt Ocean Institute has not been specified.

The largest members of this group are usually found at depths between 7,200 and 13,100 feet (2,200 to 4,000 m), according to the Monterey Bay Aquarium Research Institute.

Instead of spinning webs or creating burrows as land spiders do, sea spiders use a specialized tube-like mouth structure, called a proboscis, to slurp up prey such as sea anemones, jellies and other invertebrates.

This latest footage was taken by remotely operated vehicle pilots as part of the Schmidt Ocean Institute's South Sandwich Islands expedition, a mission to locate and describe new species in these frigid waters. According to the institute, scientists have discovered only 10% of ocean life.

A flame skimmer hovers 2 feet (0.6 meters) from my face, looking straight at me. Its red bulbous eyes have 24,000 corneas, allowing it to see 360 degrees — up, down, backward, forward and around simultaneously. What it makes of me visually is unimaginable.

It has 30 opsins, the universal photoreceptor molecule that resides in the visual systems of the animal kingdom. I look back with my three opsins and two blue corneas. At the fishpond where I am sitting, the skimmer hovers and dashes about with its satin wings, red and orange, body and wing. My visitor weighs 0.1 ounces (2.8 grams) and darts around at speeds up to 60 mph (96 km/h) for the few weeks it lives in the air.

Its three- to four-year lifespan is mainly spent as larva, a freshwater nymph, an underwater omnivore feeding on tadpoles, spot tails, minnows and other nymphs. Today, it is sporting iridescent wings that sparkle like ball gowns, looking to mate, which it prefers to do immodestly in the air. As it sparkles and pulsates in front of me, perfectly stationary, I am looking at 350 million years of evolution.

Dragonflies' compound eyes see ultraviolet light, giving them a unique ability to detect shape and movement. Military experts have studied their behavior to develop software for stealth aircraft because they employ active motion camouflage. When a dragonfly hunts, it hovers perfectly still and positions itself between its prey and a shadow cast behind it by, say, a tree, concealing its position. It's a bit like creeping up on someone in a forest hiding behind branches. The dragonfly can continually change its position based on where its prey moves to keep the tree and its prey lined up — a butterfly or mosquito won't notice. The dragonfly gradually looms closer until it reaches striking distance. This evolutionary adaptation has suited dragonflies well, and they have become highly successful predators despite living short lives.

A remarkable example of Indigenous observational science was revealed in 1949. Ethnoentomologists documented how the Diné (Navajo) named and classified over 700 species of insects, describing their sounds, behavior and habitats, knowledge that had been shared, memorized and passed on for generations. Why did the Navajo do this? Maybe because they are scientists. They wanted to know their world better, knowledge that could be the difference between surviving and thriving for people who live completely on and with the land.

In the forests of Mexico resides the giant owl butterfly (Caligo eurilochus) that flaps its papery 7-inch (18 centimeters) wings at dusk when predator birds are absent. At the base of each wing is a perfectly formed eyespot that, together, uncannily resemble the eyes of an owl. An artist would be challenged to create such replicas.

English naturalist Henry Walter Bates first explained the copycat wings. Arriving in 1848, Bates traveled far up the Amazon and its tributaries. Aside from its racist tropes, his book, "The Naturalist on the River Amazons," is a stunning description of 11 years of study wherein he collected over 14,000 species and identified 8,000 new ones, from mundane foraging ants to jaw-dropping, foot-wide, bird-eating Mygales spiders that giggling children paraded around leashed like a pet dog.

Like other naturalists of his day, John James Audubon and Alphonse Dubois, Bates shot birds right and left to be packed in formaldehyde and handed over to natural history museums. However, his primary interest was Amazonian butterflies.

He noticed edible butterflies being ignored by insectivorous birds and dragonflies because their wing coloring mimicked noxious or predatory species. The spicebush swallowtail caterpillar (Papilio troilus) is born black and white disguised as bird poop. It will molt three more times with spots on its head that make it appear like a snake — known as Batesian mimicry.

This evolutionary process rewarded deceptive wing patterns and coloring to protect species. He was an early supporter of Darwin's theories of evolution, and Darwin called Bates's book the best on natural history ever published in England.

What neither Darwin nor Bates could explain is how butterflies manage to disguise themselves. Had caterpillars ever looked at an owl's eye? They evolved, to be sure, and failures are gobbled up, but how exactly does the pupa of a caterpillar morph into a butterfly with perfect replicas of owl eyes on its wings?

The scientific explanation is a regulatory network that allows genes to collaborate and learn from each other. That does not tell us how the genes were programmed in the first place. Millions of years ago, genes began to paint wings with pigmented designs of extraordinary fidelity and complexity. Who was the artist?

To delve deeper into Paul Hawken's work, you can read an interview with the author here, in which he tells Live Science about the paradigm shift needed to start valuing, protecting and restoring the planet and its inhabitants.

Researchers believe the iguanas made the more than 5,000 mile (8,000 kilometer) journey on rafts made of vegetation, arriving in Fiji shortly after the islands formed. "You could imagine some kind of cyclone knocking over trees where there were a bunch of iguanas and maybe their eggs, and then they caught the ocean currents and rafted over," lead author Simon Scarpetta, lead author and assistant professor of environmental science at the University of San Francisco, said in a statement.

Fiji's bright-green lizards are the only iguanas outside the Western Hemisphere, and how they got there has been a long-standing mystery. In a new genetic analysis published Monday (March 17) in the journal PNAS, researchers found Fiji's iguanas are much more closely related to their Western Hemisphere cousins than previously believed, making the journey directly from the West Coast of the United States to Fiji about 34 million years ago.

"That they reached Fiji directly from North America seems crazy," study co-author Jimmy McGuire, professor of biology at the University of California, Berkeley, said in a statement. "But alternative models involving colonization from adjacent land areas don't really work for the time frame, since we know that they arrived in Fiji within the last 34 million years or so."

Related: Labord's chameleon — the color-changing lizard that drops dead in 4 months

Previously, some biologists posited the Fijian lizards — which comprise the genus Brachylophus — descended from a now-extinct family of iguanas that once populated the Pacific. Others have suggested the lizards could have floated shorter distances from South America and through Antarctica or Australia before finally ending up in the Pacific.

But these ideas were based on past genetic analyses that did not conclusively show how closely Fiji iguanas were related to other iguanids.

The new analysis relies on a genome-wide DNA sequence that Scarpetta collected from over 200 iguana specimens from museums around the world.

The work revealed the Brachylophus genus in Fiji is most closely related to lizards in the Diposaurus genus, which are widespread in the deserts of North America. These desert iguanas are well adapted to searing heat, so potentially had adaptations to survive the long journey.

"Iguanas and desert iguanas, in particular, are resistant to starvation and dehydration, so my thought process is, if there had to be any group of vertebrate or any group of lizard that really could make an 8,000 kilometer journey across the Pacific on a mass of vegetation, a desert iguana-like ancestor would be the one," Scarpetta said.

The researchers estimate these lineages split approximately 34 million years ago — roughly aligning with geological history of the islands' formation. "This suggests that as soon as land appeared where Fiji now resides, these iguanas may have colonized it. Regardless of the actual timing of dispersal, the event itself was spectacular," Scarpetta said.

In a first-of-its-kind discovery, a death adder has been found with three super-sharp, venomous fangs, instead of the usual two.

"This is something we've never seen before," Billy Collett, park manager at the Australian Reptile Park, where the snake lives, said in a statement emailed to Live Science. "We've had this death adder in the venom program for about seven years, but only recently did we notice the third fang. I thought it would just shed off over time, but one year later, and it's still there!"

This third fang, located right next to one of the other fangs at the left side of the snake's mouth, also produces venom. This means it has a much larger venom output per bite than is usual for a death adder, making it even more deadly.

This ultra-rare snake "might actually be the most dangerous death adder in the world," Collett said in a video interview. According to the statement, the extra fang is the result of a never-before-seen mutation.

Related: 'Truly primal': Watch Burmese python swallow deer whole in Florida Everglades by stretching its mouth to the absolute limit

Death adders (Acanthophis) are a group of venomous snakes native to Australia and New Guinea. They have one of the fastest strikes of any snake, with some species being capable of biting and injecting venom from their fangs in under 0.15 seconds. Their venom contains neurotoxins that can cause paralysis and even death if left untreated. Before the development of antivenom, around 50% of death adder bites were fatal.

This snake is part of Australian Reptile Park's antivenom production program, and its extremely rare extra fang was discovered when it was being milked for its venom. This involves gently squeezing a snake's venom glands while it bites onto a collection container, causing the venom to pour into the vial.

This three-fanged death adder was found to produce far more venom than usual, with "massive yields" coming out of all three fangs. It produces roughly double that of a two-fanged death adder — although it's unclear whether the higher yield is the result of the extra fang, or that this individual just produces high quantities of venom.

This is the first three-fanged snake ever discovered at the Australian Reptile Park, which has been operating for 20 years and has milked hundreds of thousands of snakes, a spokesperson for the park told Live Science in an email.

"There have been other 3 fanged snakes found in Australia, but from what we can find, there have been no 3 fanged death adders recorded," they said.

Exactly why this snake has three fangs instead of two is unclear, but may be related to the process of fang replacement. Similar to human adult teeth, death adders have replacement fangs growing behind the active ones, so when a fang is lost, a new one moves forward to take its place. This ensures that their fangs remain sharp and functional for injecting venom.

"It's normal for death adders to shed fangs over time and replace them with new ones every few months or so," the spokesperson said. "Unfortunately, we don't actually know what has caused the 3rd fang to develop and don't currently have the facilities to run any tests."

They attempt to revive companions by licking at their faces, or even by pulling at their mouths or tongues, according to a study published Feb. 21 in the journal Science.

More aggressive mouth-pulling, biting and licking behaviors were seen in mice that had spent more time with the mouse in need of help, resulting in a faster recovery, the researchers report.

"The most striking discovery in this study is the existence of instinctive emergency responses in animals to revive unconscious — and even freshly deceased — partners. This study provides the first documented evidence of resuscitation-like behavior in naïve, untrained mice," study lead author Wenjian Sun, a researcher at the University of Southern California, told Live Science in an email.

Helping other animals that are injured or sick has been observed in a number of species, including dolphins, elephants, and non-human primates, Sun explained.

Related: Ants perform life saving operations — the only animal other than humans known to do so

"These behaviors often include touching, grooming, nudging, and, in some cases, more intense physical actions such as striking. However, specific behaviors like tongue biting and tongue pulling, as observed in this study, have not been previously reported," Sun said.

In the paper, the researchers describe how dozens of mice reacted after being introduced to another mouse in a state of need. These states included the other mouse being stressed and unconscious.

Mice spent more time in physical contact with the other mouse if it was unconscious rather than awake, with the intensity of the grooming increasing over time if the other was unconscious. Mice spent an average of 47% of the 13-minute test interacting with an unconscious partner.

Grooming increased in vigor over the test period from sniffing and licking to biting at the other mouse's mouth and tongue, with more aggressive actions being seen in pairs of mice that were more familiar with one another. Over 50% of the mice ended up pulling at the tongues of their unconscious companion.

The mice were also able to detect that their companion was unconscious without relying on visual cues, initiating the grooming behaviors even in the dark.

The more intense grooming behaviors were correlated with better recovery in the unconscious mice, with a more rapid return to consciousness afterwards. When their companion awoke, the first-aider mouse stopped performing the grooming behaviors.

"The animal appears to be able to recognize the unconscious state of its partner, with the unresponsiveness triggering the behavior and regaining of responsiveness terminating the behavior," Sun said.

While these findings indicate that mice have an instinct to help others like humans do, the researchers can't be certain why they act in this way.

"We do not exclude the possibility that the animal is simply driven by instinctive impulses to perform these actions — an instinct that may have evolved over time during evolution — rather than acting with a conscious intent to revive its partner," Sun said.

In another paper, also published on Feb. 21 in Science, other researchers from the University of California, Los Angeles describe the neuronal mechanisms behind this behavior. They found that the grooming is likely driven by the release of oxytocin — a hormone that plays a crucial role in social bonding, sex, and childbirth — in areas of the brain called the amygdala and hypothalamus.

"Inactivation of oxytocin neurons or blocking oxytocin receptors impaired the behavior, confirming that oxytocin is essential for this emergency response. This aligns with the oxytocin's well-known role as the 'love hormone' which is associated with trust and affection in humans and promotes social bonding," Sun explained.

"Since oxytocin receptors are expressed in many brain regions, future research will focus on identifying the specific neural circuits involved in this behavior."

Where it lives: Wondul Range National Park, Queensland, Australia

What it eats: Small insects and arthropods

Why it's awesome: These colorful critters don't just dress to the nines to woo their mate. Males also do a sexy shimmy to dazzle the ladies.

Measuring no bigger than 0.2 inches (0.5 centimeters), the sparklemuffin peacock spider is, arguably, one of the cutest spiders around. These jumping spiders were discovered as a new species in 2015.

Females are a dull brownish gray but — like their namesake, the peacock — male sparklemuffins pull out all the stops in the outfit department. With their striking red and blue backs, they look similar to kicking peacock spiders (Maratus calcitrans) and fingers peacock spiders (Maratus digitatus).

But they have a secret up their sleeve that makes them unique: a small flap on the side of their abdomen that they can extend to show off iridescent blue scales.

In case their gaudy garb isn't enough to impress, the males also know how to bust a move. Their Latin name (jactatus) means "rocking" or "jolting" because of the thrusting dance they perform for prospective mates.

Related: Surprisingly-bad acting is key to jumping spider's survival

During courtship, males unfold their fan — a flap on their abdomen used in courtship — and tilt it to one side. At the same time, they lift up their third leg on the same side, lower it slowly then whip it back up, like someone teasing a dog by dangling its toy just out of reach. This jerking motion makes their whole body waggle around, creating vibrations that the female can sense through the ground.

"When [the male] got within a few centimeters of the female, he exploded into a firework of activity," entomologist Jürgen Otto, who wrote the paper describing the species and runs the website Peacock Spider, previously told Live Science.

The species was discovered by a graduate student called Madeline Girard who nicknamed it "sparklemuffin." She discovered another species at the same time and gave it the moniker “Skeletorus” because of its striking black and white markings that look like a Halloween skeleton costume.

Otto believes there could still be many more species of peacock spider out there. "Despite the large number of species we have discovered just in the last few years, I can't help feeling that we may have just scratched the surface of this most exciting group of spiders," he said, "and that nature has quite a few more surprises in store."

Editor's note: This story was updated at 12:40 p.m. ET to correct a measurement conversation.

Dolphins live in almost every ocean, except most tend to avoid the cold waters in the Arctic and around Antarctica. Some also live in rivers, including the Amazon River in South America and the Ganges River in India.

Dolphins are technically classified as whales, but are different from their larger cousins in many ways. The largest dolphin species is the orca, which measures up to 32 feet (9.8 m) long, while the smallest species is the Hector's dolphin, which grows to only 4.8 feet (1.5 m) long.

Dolphins live and hunt in large social groups called pods, and they communicate with each other using high-pitched clicks and whistles. They are very intelligent because they have to work together to hunt down prey.

Dolphins also love to play. You can often spot them surfing waves, toying with seaweed, and even interacting with other species for fun. Some species can swim incredibly fast, with the short-beaked common dolphin hitting speeds of up to 37 mph (60 km/h) — about as fast as a car driving on city streets.

5 fast facts about dolphins

• Dolphins use tools to find food. Some dolphins cover their beaks with sponges while searching for food on the seafloor. Others use empty shells to trap fish.
• Dolphins live in social groups called pods. Pods usually have two to 30 dolphins, but some dolphins live in superpods of over 1,000 animals.
• Dolphins use a language of clicks and whistles, called echolocation, to track down their prey and create a mental map of their surroundings.
• Some dolphin species live in freshwater rivers, like the Amazon.
• Despite their name, killer whales (orcas) are actually dolphins.

Everything you need to know about dolphins

Dolphin pictures

Discover more about dolphins

—The weird reason dolphins drink each other’s pee

—Watch a huge megapod of acrobatic spinner dolphins in incredible, rare video

—Orcas: Facts about killer whales

Whales are a group of mammals that live in oceans. They include some of the largest animals on Earth. The blue whale is the biggest animal that has ever existed. Whales can be found in every ocean, with many species migrating long distances between their feeding and mating grounds, where they gather to have babies.

There are over 90 whale species. Some of the most famous whale species are humpback whales, sperm whales, blue whales and narwhals. Despite their name, killer whales — or orcas — are not whales. Instead, they are part of the closely related dolphin family.

Many whale species were hunted for their oil and other body parts during the 1800s and 1900s, and they almost went extinct. Even though this practice has been banned in most countries, some whale species still have very small populations and are considered vulnerable, endangered or critically endangered.

5 fast facts about whales

• Cuvier's beaked whales hold the record for the deepest-diving mammal. They can go nearly 10,000 feet (3,000 m) below the water's surface — about 10 times deeper than the Eiffel Tower is tall..
• Some whales, such as humpback whales, are known for their long and complex songs, sometimes lasting up to 22 hours.
• Whales are not fish, so they cannot breathe underwater. Instead, they use the blowholes on the top of their head to breathe air at the ocean's surface.
• Whales evolved from a deer-like land mammal called Pakicetus about 50 million years ago.
• A sperm whale's brain weighs about 17 pounds (8 kilograms) — about five times heavier than a human brain — making it the largest brain of any known animal.

Everything you need to know about whales

Whale pictures

Discover more about whales

—Humpback whales: Facts about the singers of the sea

—Will humans ever learn to speak whale?

—Why some whales go through menopause

Dinosaurs are the extinct relatives of birds that roamed the lands and seas of ancient Earth. They first appeared around 240 million to 230 million years ago in the Triassic Period, and went extinct around 66 million years ago, at the end of the Cretaceous Period, when a massive asteroid slammed into Earth.

During the Triassic Period, when dinosaurs first evolved, all the continents we know today were clumped together in a single landmass called Pangaea. Over tens of millions of years, Pangaea split apart, eventually coming to resemble the map of the world we know today. Dinosaur fossils have been found on every continent around the globe, including Antarctica.

Some of the most famous types of dinosaurs include Tyrannosaurus rex, Triceratops, Stegosaurus and Velociraptor, many of which were featured in the popular "Jurassic Park" movies. Most of these dinosaurs lived tens of millions of years apart from each other.

Dinosaurs belong to a group of animals known as archosaurs, which also includes modern-day animals such as birds and crocodiles.

5 fast facts about dinosaurs

• The heaviest known dinosaur is thought to be Argentinosaurus, a supermassive titanosaur that lived during the Cretaceous period. It may have weighed up to 180,800 pounds (82,000 kilograms).
• An asteroid wiped out the dinosaurs. The crash left a giant crater around 110 miles (180 kilometers) wide off Mexico's coast.
• The word "dinosaur" means "terrible lizard" in Latin, and it was first made up in 1842 by paleontologist Richard Owen.
• Birds are actually dinosaurs. They evolved from theropods, a group of mostly meat-eaters that included Velociraptor and T. rex.
• Pterodactyls are flying reptiles that lived at the same time as the dinosaurs, but they are not actually dinosaurs.

Everything you need to know about dinosuars

Dinosaur pictures

Discover more about dinosaurs

—A brief history of dinosaurs

—Mesozoic era: Age of the dinosaurs

—What if a giant asteroid had not wiped out the dinosaurs?

The tusk was sitting in the drainage area of a creek bed on the O2 Ranch in Brewster and Presidio counties near Big Bend National park, according to a statement released by Sul Ross State University in Texas.

Columbian mammoths (Mammuthus columbi), a distant southern cousin of woolly mammoths (Mammuthus primigenius), lived on the grasslands of what are now North and Central Texas up until around 11,700 years ago, according to the Texas Master Naturalists website, hosted by Texas A&M University. However, the discovery of mammoth remains in West Texas is very rare.

"Seeing that mammoth tusk just brings the ancient world to life," Will Juett, the O2 ranch manager, said in the statement. "Now, I can't help but imagine that huge animal wandering around the hills on the O2 Ranch. My next thought is always about the people that faced those huge tusks with only a stone tool in their hand!"

Related: Poll: Should we bring back woolly mammoths?

Columbian mammoths coexisted with humans until the animals went extinct at the end of the last ice age. Researchers have proposed several potential causes for their extinction, including climate change, hunting by humans and disease, according to Texas Master Naturalists.

The hunter who found the tusk, who isn't named in the statement, took photos of the fossil inside the creek bed and showed them to Juett. The ranch manager then contacted Bryon Schroeder, director of the Center for Big Bend Studies at Sul Ross State University, and another archeologist. They contacted additional researchers and investigated the discovery.

Schroeder verified that it was a mammoth tusk, and the researchers spent two days excavating it from the ranch. They covered the tusk in strips of plaster-covered burlap to protect it and then built a frame to transport it to Sul Ross State University. During the excavation, the researchers didn't find any other mammoth parts.

"We realized pretty quickly there was not more to the skeleton, just an isolated tusk that had been separated from the rest of the remains," Schroeder said in the statement.

The researchers are now awaiting the results of carbon dating tests to tell them how old the mammoth tusk is, according to the statement.

Mammoth quiz: Test your knowledge of the ice age beasts

The newfound species is called Clavusodens mcginnisi, or McGinnis' nail tooth. The animal lived 340 million years ago and belonged to a group of sharks known as obruchevodid petalodonts, or "chipmunk sharks" because of their tiny size and unusual teeth.

These sharks grew to just 3 to 4 inches (7.5 to 10 centimeters) long and fed on crustaceans, worms and other prey on the seafloor, according to a statement released by the National Park Service (NPS). It's thought their tiny size helped them avoid large predators while foraging.

Researchers unveiled McGinnis' nail tooth in a study published Jan. 24 in the Journal of Paleontology. The species name is named after David McGinnis, a retired National Park Service superintendent, and their teeth, which resemble old iron nails.

Related: 325 million-year-old shark graveyard discovered deep within Mammoth Cave harbors new fossilized species

Mammoth cave

A team of researchers plucked the fossils out of rocks inside Mammoth Cave, the longest cave system in the world. Mammoth Cave is a treasure trove for ancient fish fossils, with more than 70 different species identified within its walls, according to a 2024 study published in the journal Parks Stewardship Forum.

Underground rivers and streams forged the cave's passages, which are made up of rocks that have preserved marine sediment from the Carboniferous period (358.9 million to 298.9 million years ago). The cave has given researchers a unique window inside these rocks, and therefore the marine environments they preserve, according to the 2024 study.

Researchers have been documenting vertebrate fossils in Mammoth Cave since 2019. The work is challenging because of the cave's often cramped conditions and limited space to move equipment in and out.

"Many of these sites have low ceilings requiring crawling for long distances on hands and knees, and at times belly crawling," the researchers wrote in the new study. "The fish fossils are frequently encountered in the cave ceilings or walls."

The newly discovered fossils came out of the Ste. Genevieve rock formation and date back to 330.9 million to 323.2 million years ago. The fossils are the oldest obruchevodid petalodonts discovered so far, according to the study.

Researchers suspect that these ancient sharks may have lived in reef-like systems filled with marine invertebrates called crinoids, or sea lilies, that attached themselves to the sea floor like plants. However, that assessment remains speculative until researchers carry out more studies on the ancient fish and their habitat, according to the study.

Discoveries like McGinnis' nail tooth enable researchers to learn more about long-extinct sharks and the ecosystems they inhabited.

"The fossil discoveries in Mammoth Cave continue to reveal a wealth of new information about ancient shark species," Barclay Trimble, the superintendent at Mammoth Cave National Park, said in the statement. "Researchers and volunteers collected samples from the main Mammoth Cave system and from smaller isolated caves throughout the park that have provided new data on previously known ancient sharks and revealed several species that are brand new to science."

The fossil was spotted at the base of a cliff on the Isle of Skye in Scotland in 1973, but it was not collected by paleontologists for another 45 years due to its tricky location.

Now, according to a paper published March 6 in the journal Earth and Environmental Science Transactions of the Royal Society of Edinburgh, this fossil — which includes fragments of a spine, ribs, and hip bones — may be the remains of a dinosaur that lived during the Jurassic Period (201.3 and 145.0 million years ago).

This fossil, nicknamed the "Elgol dinosaur" after the village near where it was found, is now considered the most complete dinosaur fossil ever discovered in Scotland, as well as being the earliest ever unearthed there.

Located off the northwestern coast of Scotland, the Isle of Skye is the location of several dinosaur fossils and footprints from the Middle Jurassic period, which is poorly represented in the global fossil record.

Related: Megalodon may have grown up to 80 feet long — far larger than previous estimates

"This is a wonderful addition to the rapidly growing set of Jurassic finds from the Isle of Skye which are enabling us to learn more and more about the rich ecosystem of the time," study co-author Stig Walsh, a senior curator of vertebrate palaeobiology at National Museums Scotland, said in a statement.

The newly identified dinosaur may have been about the size of a pony, and was at least eight years old when it died, according to the researchers.

The fossil was first recorded by paleontologists during field trips between 1971 and 1982, with a 1973 notebook entry mentioning "bones of a dinosaur" in a cliff with a small sketch. The original discoverers didn't realize its significance, and due to its awkward location, it was exceedingly difficult to remove from the ground.

Researchers rediscovered the fragmented fossil in 2015, and itwas eventually excavated and transported from its cliff location in 2018.

"This was a really challenging extraction, in fact we'd previously felt was too difficult to collect the fossil, but I thought it was really important to study it," study lead author Elsa Panciroli, a NERC Independent Research Fellow at National Museums Scotland, said in the statement.

"I was able to persuade the team to give it a try. It took a lot of hard work from a lot of people, but we did it: finally we can confirm and publish Scotland's first recorded and most complete dinosaur, and that makes it all worthwhile."

Paleontologists then studied the fossil using a range of techniques, including micro-CT scanning, which is a non-destructive imaging technique that uses X-rays to create highly detailed 3D images of small objects at a microscopic scale.

The shape and microstructure of the bones, and the fact they were found within the Kilmaluag Formation — a geological formation dating to the Middle Jurassic — indicated that the fossil may be the remains of a cerapodan or ornithopod dinosaur.

Cerapodan dinosaurs are a major group of ornithischian (bird-hipped) dinosaurs, which have a pelvic structure resembling that of modern birds. Ornithopods are one herbivorous sub-group of cerapodans that lived during the Jurassic and Cretaceous periods, and had beaked mouths for cropping vegetation. One of the most well-known groups of ornithopods were Iguanodons, which were one of the first dinosaurs ever named.

If this new dinosaur is indeed ornithopodan, it may be among the earliest ornithischian fossils, and possibly the oldest ornithopodan body fossil in the world.

"Some aspects of the bones indicate that the specimen may be an ornithopod, a group of plant-eating dinosaurs that are best known from the Cretaceous," study co-author Susie Maidment, a paleontologist at the Natural History Museum in London, said in the statement.

"This specimen, however, would already have been a fossil by the time that the better-known ornithopods like Iguanodon and Hypsilophodon were walking the Earth," she said. "Recent research on the fossils of Elgol has revealed a diverse ecosystem of extraordinarily preserved Middle Jurassic animals, and I'm sure there are more exciting discoveries to come."

These massive sharks may also have been more slender than originally believed, the researchers said.

"Previous estimates using teeth to predict its size had the shark reaching about 18-20 meters total length (59-65 feet)," study co-author Phillip Sternes, an educator at SeaWorld San Diego, told Live Science in an email.

Megalodon ruled the seas of ancient Earth between around 20 million and 3.6 million years ago. No complete megalodon (Otodus megalodon) skeletons have ever been found, so our knowledge of these behemoths comes from fossils of their vertebrae scales and teeth. The largest megalodon fossil ever found is a 36-foot-long (11 m) section of its spine, which would have been located in the trunk of its body.

In the new study, published Sunday (March 9) in the journal Palaeontologia Electronica, researchers examined megalodon fossils and compared them with more than 150 living and extinct shark species to build a better picture of just how big this giant shark was.

The researchers compared the proportions of the megalodon's trunk with the trunks of 145 modern and 20 extinct shark species.

Related: What did 'the meg' look like? We have no idea

Assuming that the megalodon was roughly proportional to the majority of other shark species, and extrapolating from the 36-foot (11 m) trunk section, the researchers estimated that this individual may have had a 6-foot-long (1.8 m) head and 12-foot-long (3.6 m) tail, giving it a total length of 54 feet (16.4 meters).

However, the largest megalodon vertebra ever found measured up to 9 inches (23 centimeters) in diameter — 3 inches (7.6 cm) bigger than the largest vertebra from the 54-foot shark. Scaling up from this larger vertebra, and based on the previous proportions, the megalodon it belonged to may have measured 80 feet long.

The researchers also found that the megalodon may have given birth to live young measuring 12 to 13 feet (3.6 to 3.9 m) long.

Megalodon shape

The researchers behind the new study also investigated the megaladon's shape.

Megalodon tooth fossils are serrated and resemble the teeth of modern-day great white sharks (Carcharodon carcharias), which previously led researchers to assume that megalodon looked similar to great whites.

"Previous studies simply assumed that megalodon must have looked like a gigantic version of the modern great white shark without any evidence," study lead author Kenshu Shimada, a paleobiology professor at DePaul University in Chicago, told Live Science in an email.

However, according to the new study, the megalodon may have actually looked more slender and streamlined.

Based on the revised maximum body size, as well as hydrodynamic models of how large creatures like whale sharks (Rhincodon typus), basking sharks (Cetorhinus maximus) and whales move through the water, the researchers conclude that the megalodon wasn't stocky like a great white and instead was more similar to a lemon shark (Negaprion brevirostris).

However, until researchers find a larger section of a megalodon's body in the fossil record, we won't truly know how large they could get, or what shape their bodies may have been.

Jack Cooper, a megalodon researcher at Swansea University in the U.K. who was not involved in this new study, isn't convinced by the study authors' argument that megalodon looked more like lemon sharks than great whites.

"The hydrodynamic methods they use to try to rule out these other body forms are based primarily on whales, which have totally different skeletons and modes of swimming to sharks (i.e., vertical vs horizontal tail movements)," Cooper said. "As such, while the proposed body plan is possible, it should be treated as a working hypothesis and previous reconstructions can't yet be definitively ruled out."

Shark quiz: How much do you know about these iconic ocean superstars?

The idea is so powerful that it has made its way into popular culture, such as in Disney's "The Lion King," where haunting images of an elephant cemetery seared themselves onto the minds of a generation of children. Such graveyards hint at the tantalizing prospect that elephants might understand and anticipate their own mortality. But do these places really exist, and do elephants know when they are about to die?

In Africa and elsewhere, there are rare instances when a large number of elephant carcasses are found in a relatively confined area, said Leanne Proops, an associate professor of animal behavior and welfare at the University of Portsmouth whose research looks at death-related behaviors in animals. But in these occasional cases, the pile of carcasses has been linked to drought, large-scale poaching, geological forces or toxic algal blooms in water holes, which have been found to poison hundreds of elephants in one go.

What researchers have been unable to show is that these graveyards form because elephants intentionally traveled there to die, Proops told Live Science. "I can see where that myth or idea could have come into popular culture," she said, but that's exactly what it is: a myth, she said.

Akashdeep Roy, a researcher at the Indian Institute of Science Education and Research, agreed. "I'd be very cautious about using the term 'graveyard,'" he said. "The idea of a graveyard that persists is largely a myth fueled by locals and hunters."

Related: Do elephants really 'never forget'?

Do elephants bury their dead?

That doesn't mean elephants have no understanding or emotional experience of death. In fact, Roy's own research opens up another angle on that question, with the possibility that elephants bury their kin. In a 2024 study, Roy and colleagues documented five cases in India's North Bengal region where baby Asian elephants (Elephas maximus) had been found almost completely buried in muddy drainage ditches at separate sites on tea estates, with only their legs protruding from the soil.

The burials seemed strategic, according to Roy. The trench environment would have enabled the adult elephants to place the infants into the ditch and then scoop earth over their bodies. "The elephants buried the carcasses physically without using any tools," Roy said. "I am as confident as an elephant is in locating water sources and paddy fields. There were elephant footprints all [around] the carcass, and … it's not very difficult for elephants to level the soil over a trench."

Locals in North Bengal and neighboring Assam have found several other burial sites beyond the five Roy and colleagues documented in their paper, and village elders accept elephant burials as established knowledge, he noted. Similar scenarios have been observed in African elephants (Loxodonta), in which dead elephants have been found covered in branches and leaves.

Proops said there could be other explanations for why the calves ended up buried and cautioned that without firsthand observation of the elephants doing so, we can't be sure the burials were intentional.

"I guess the reason we're interested in it is because we want to know whether this shows they understand death," Proops said. "It's very hard to interpret, particularly when it is a rare event. For me, I don't think we can really confirm whether it's a burial, in the sense that it has this sort of cognitive meaning to it."

While questions may linger around this facet of elephant behavior, they show several other intriguing death-related practices. Asian elephants have been observed carrying dead infants for hours or days and are known to stand vigil around the bodies of deceased herd members. Studies also document elephants showing signs of distress when dealing with dead or dying elephants; in Roy's research, the elephants associated with the burials were recorded trumpeting for almost an hour when they were in the area.

"We felt that [they were mourning], but it's always difficult to anthropomorphize such behavior in a natural science journal," Roy said. "Hindu people in India revere elephants as living gods — Shiva and Ganesha — and value elephant subjectivity."

Related: Do animals grieve?

Scientists have also documented several cases in which elephants have turned up at the site of a carcass and interacted with it, curiously touching and sniffing its bones. In fact, this research showed that African elephants that were presented with the bones of several species showed more interest in the skulls and tusks of other elephants of their own species. The finding suggests that they recognize their own species in death, and that judging by the physical signs of excitement the elephants showed in the presence of the bones, that these remains elicit an emotional response, the study authors suggest.

This idea is especially tantalizing because it seems to echo the kind of reflection that humans would show in a graveyard, "a place where the dead reside, and where we actually go out of our way to visit them as well," Proops said. However, the evidence for that conclusion comes up short; in general, the research shows that elephants don't make intentional pilgrimages to commune with these carcasses. Cases where elephants do encounter dead kin seem to occur when they randomly stumble upon a pile of bones; there is no evidence of planned behavior.

"What we really need is GPS data, where we look at normal patterns of movements in the elephants and we see them obviously deviating from those normal routes to go and visit a particular carcass," Proops said.

The truth is that we don't know if elephants understand that they're going to die one day. "There really is no strong evidence that other species do understand that," Proops said.

Known for their extraordinary intelligence, elephants are recognized as some of the world's most empathic creatures, working together in close-knit communities to help one another. They are even known to grieve and bury their dead.

But how much do you know about these giants? Take our quiz to find out. If you need a hint, tap the lightbulb in the top right corner.

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The scaleless fish is a previously unknown species of golden-line fish (Sinocyclocheilus), which are only found in and around Chinese caves. The discovery therefore offers scientists a window into the evolution of these unusual cave-dwelling creatures.

Some golden-line fish have lost their scales and eyes as part of adaptations to cave life — there's no point having eyes if it's too dark to see anything. The newfound species, which the researchers named "Xingren golden-lined fish" (S. xingrenensis) after the city close to where it was found, has large eyes but no scales, suggesting it is still evolving to suit its conditions, according to the study, published Feb. 24 in the journal Zoosystematics and Evolution.

Previous research suggested that golden-line fish moved into caves when China was drying up — so there was less water outside — towards the end of the Miocene epoch (23 million to 5.3 million years ago) and in the Pliocene epoch (5.3 million to 2.6 million years ago). By examining the evolutionary history of golden-line fish, the study authors found that Xingren and others like it probably lost their scales during the Pleistocene (2.6 million years to 11,700 years ago), similar to when some members of the group supposedly started losing their eyes.

"This further suggests that most cave fishes may not have lived in cave ecosystems for more than a few million years," the researchers wrote in the study. "Thus, together with the eyes and scales, we hypothesize that the new species may be undergoing a gradual evolutionary process towards caves."

Related: Do fish get thirsty?

Sinocyclocheilus is the most diverse group of cave fish in the world with 80 recognized species — the Xingren golden-line fish makes 81. Researchers found this latest addition to the group while collecting golden-line fish in southwestern Guizhou province between 2012 and 2020, according to the study.

Golden-line fish are strikingly varied in appearance. The newfound species differs from known golden-line fish thanks to a unique combination of features, including having a scaleless body with irregular black markings. Xingrens also lack a horn-like structure present on some golden-line fish, notably S. longicornus, a unicorn-like blind fish discovered in 2023.

Researchers still have much to learn about Xingrens, but their eyes offer some clues about how this species lives. The researchers suggested that Xingrens' lives are linked to photoperiods, which are the lengths of daylight periods an organism receives within 24 hours. After all, Xingren eyes are significantly larger than the blind fish found in total darkness deep in caves, and can therefore still detect light.

"This is related to the habitat, where the new species can be connected to surface streams through cave windows, and their life rhythms may be closely related to photoperiods," the study authors wrote.

Colossal scientists used mice because their shorter gestation period makes it much easier to test the gene edits and engineering tools needed to do the same procedure on elephants, in the hope that one day they could "resurrect" woolly mammoths (Mammuthus primigenius).

But is this something we should even be doing? Take our poll and let us know what you think in the comments below.

The punch of a peacock mantis shrimp (Odontodactylus scyllarus) is the strongest self-powered strike by an animal. They use hammer-like fists, or dactyl clubs, to shatter prey's shells. The strike is so strong it can even break aquarium glass, delivering a force comparable to a .22 caliber bullet.

But because these high-impact strikes generate a lot of force, scientists have puzzled over how the critters can withstand the intense shock waves generated by their own attack.

In a new study published Feb. 6 in the journal Science, researchers examined the structure of the shrimps' clubs. Their findings revealed that the microstructure of these clubs act as natural shock absorbers to limit damage.

"We found it uses phononic mechanisms — structures that selectively filter stress waves," study co-author Horacio Dante Espinosa, a professor of mechanical engineering and biomedical engineering at Northwestern University, said in a statement. "This enables the shrimp to preserve its striking ability over multiple impacts and prevent soft tissue damage."

Powerful punch

Peacock mantis shrimp use a complex system of biological latches and springs in their dactyl clubs to unleash a punch at a speed of 75 feet per second (23 meters per second), according to a 2004 study — 50 times faster than the blink of an eye.

While this immense speed helps deliver a powerful blow, it also creates dangerous shock waves.

"The strike is so fast that it creates cavitation bubbles, which, upon collapsing, generate additional shockwaves, effectively delivering a double impact," Espinosa said.

Previous research theorized that the microstructure of the dactyl clubs helps protect the shrimps from these shock waves.

In the new study, the scientists tested this theory using advanced laser-based techniques to analyze how different wavelengths move through the peacock mantis shrimp's dactyl clubs.

The findings revealed two important regions in these clubs that help them survive their own strikes: the impact region and the periodic region.

The impact region is composed of a layer of chitin fibers arranged in a herringbone pattern that reinforces the club against fractures.

Beneath this layer is the periodic region, made from twisted arrangements of layered chitin fibers. This type of helicoidal structure is known as a Bouligand structure and is found in fish scales and lobster exoskeletons to provide strength and fracture toughness.

The laser tests measured the speed of acoustic stress waves through both regions. These waves passed through the impact region unchanged but moved at varying speeds through the periodic region — suggesting the latter region causes high-frequency waves to disperse to reduce the intensity.

The researchers also discovered that the periodic region filtered out high-frequency shock waves — which can cause significant damage to tissues, according to the statement.

The high-frequency waves were likely generated when the cavitation bubbles collapsed.

"We connected this high frequency to the frequency generated by bubble collapse during the impact event," Epinosa said.

The bundles of fibers in the periodic region act like a "phononic shield," actively blocking, redirecting and scattering waves, and ultimately preventing any harmful shock waves from traveling efficiently through the layer. This protects the delicate tissues of the mantis shrimp from the resulting shock waves of the cavitation bubble.

"The research provided experimental evidence that the Bouligand structure of the mantis shrimp's dactyl club functions as a phononic shield, selectively filtering high-frequency shear waves generated during impact," Espinosa said.

"These features help protect the mantis shrimp's club from damage by mitigating high-frequency stress waves, making it a naturally optimized impact-resistant structure," Epinosa said.

According to the press release, this study could be applied to the development of sound-filtering materials for protective gear and inspire new approaches to reduce blast-related injuries in the military and high-impact sports.

The venomous scorpion was larger than many ancient — and modern — scorpion species. Researchers believe it would’ve been a key species in the food chain, gobbling up spiders, lizards and even small mammals that lived in its ancient ecosystem.

It is just the fourth terrestrial scorpion fossil to be found in China and the first Mesozoic-era scorpion fossil found in the country, researchers reported Jan. 24 in the journal Science Bulletin.

Most scorpions from the Mesozoic era (252 million to 66 million years ago) are preserved in amber. Fossilized scorpions are much rarer because these arachnids live under rocks and branches, where they're less likely to be trapped in sediment and fossilize, said study co-author Diying Huang, a researcher at the Nanjing Institute of Geology and Palaeontology in China.

The scientists found the fossil in the Yixian Formation, a hotbed of Early Cretaceous fossils in northeastern China. The team named the new species Jeholia longchengi. "Jeholia" refers to the Jehol Biota, the ecosystem of northeast China in the Early Cretaceous about 133 million to 120 million years ago, and "longchengi" refers to the Longcheng district of Chaoyang, China, where the fossil currently resides.

J. longchengi was roughly 4 inches (10 centimeters) long, making it something of a giant of its time. "Other Mesozoic scorpions are much smaller, most of them less than half [the size] of the new species," Huang told Live Science in an email.

Related: What if a giant asteroid had not wiped out the dinosaurs?

J. longchengi has a pentagonal body and rounded spiracles, which are the openings in its body that allowed it to breathe. These characteristics are similar to those found in some families of modern-day scorpions that inhabit other parts of Asia. But unlike those families, J. longchengi has fairly long legs and slim pedipalps, or pincers, that lack spurs along a segment called the patella.

Fossils of many other animals — including dinosaurs, birds, mammals and insects — have been found in the Jehol Biota, suggesting a complex food web. Larger mammals and dinosaurs may have preyed upon J. longchengi, while the scorpion's diet may have included insects, spiders, frogs and even small lizards or mammals, the researchers wrote in the study.

The scorpion's mouthparts aren't preserved in the fossil, though, so it's hard to know for sure what they ate. Discoveries of additional fossil specimens could clear up the species' role in the ecosystem and its place in the food web, the researchers wrote.

"If placed in today's environment, it might become a natural predator of many small animals, and could even hunt the young of small vertebrates," Huang told China’s state run Xinhua news agency.

The fossil is being stored at the Fossil Valley Museum in Chaoyang, China.

There are about 4,000 different snake species in the world today. They occupy a wide range of habitats — some dwell underground while others live high in the canopies of trees, and many spend their entire lives on the ground. Some even spend a significant portion of their lives underwater. They have adapted to climates ranging from tropical rainforests and deserts to marine environments and the freezing Arctic.

These legless reptiles evolved from four-legged lizards during the Jurassic period (201 million to 145 million years ago). Like nearly all living reptiles, snakes are cold-blooded, meaning they rely on the environment to regulate the temperature of their bodies. As a result, snakes are frequently seen warming themselves in the sun.

Though snakes are often thought to be dangerous, only around 600 species are venomous, about a third of which possess venom that is fatal to humans, according to National Geographic. Even these species are inclined to avoid humans and only strike when threatened. Most snakes are entirely harmless, and they are all crucial predators that help maintain food webs.

4 fast facts about snakes

• Snakes smell by flicking their forked tongues and picking up odors that are transported to special organs on the roofs of their mouths.
• Snakes do not have eyelids. Each eye is covered by a clear membrane that is periodically shed along with the skin.
• Some species of snake have the remnants of legs in the region where their lizard ancestors would have had legs.
• All snakes shed their skin. They do this to grow and remove parasites.

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The biotechnology company Colossal Biosciences unveiled images and footage of the woolly mice on Tuesday (March 4). The adorable rodents mark a milestone in Colossal's project to bring back woolly mammoths by 2028, the company said in a statement shared with Live Science.

"We actually just started this work in mice in September [2024]," Ben Lamm, Colossal's co-founder and CEO, told Live Science. "We didn't know they were going to be this cute."

Colossal scientists plan to eventually "resurrect" woolly mammoths (Mammuthus primigenius) by first editing cells from the mammoths' closest living relatives, Asian elephants (Elephas maximus), to create elephant-mammoth hybrid embryos with shaggy hair and other woolly mammoth traits. But before the researchers can start working with elephants, they must test the relevant gene edits and engineering tools in mice, which are easier to keep and quicker to breed.

Related: Woolly mammoth de-extinction inches closer after elephant stem cell breakthrough

"A mouse model is super useful in this case, because unlike elephants [whose gestation lasts about 22 months], mice have a 20-day gestation," Beth Shapiro, an evolutionary biologist and chief science officer at Colossal, told Live Science.

The short gestation period enabled researchers to design, clone and grow the woolly mice in just six months, Lamm and Shapiro said. Colossal scientists described the results in a study that was uploaded to the preprint database BioRxiv March 4. The study has not been peer reviewed.

Fluffy rodents

To create the woolly mice, the researchers modified seven of the rodents' genes, six of which were related to fur texture, length and color. The scientists selected these genes by screening for DNA sequences that control hair growth in mice and have evolutionary links to sequences that gave woolly mammoths shaggy hair.

"We haven't taken mammoth genes and put them into a mouse," Shapiro said. "We've looked for the mouse variants of the genes that we think are useful in mammoths and then created mice that have many of these edits simultaneously."

Most of the edits "switched off" genes that are usually active in mice. For example, the scientists blocked a gene called FGF-5 that regulates hair length, resulting in mice with fur that is three times longer than standard laboratory mice.

The team also gave the mice mutations that existed in woolly mammoths, resulting in wavier fur than normal mice. Woolly mammoths had a truncated version of a gene called TGF alpha, as well as a mutation in the keratin gene KRT27, which the scientists incorporated into woolly mouse DNA.

The researchers used three genetic engineering techniques to add the edits into a single organism, including a technology called multiplex precision genome editing, which enables researchers to edit several DNA sites at once with high precision.

"It's definitely a proof of concept that you can incorporate multiple mutations into a single mouse and make its hair look like mammoth hair," Vincent Lynch, an evolutionary biologist and associate professor at the University at Buffalo who is not involved in the Colossal research, told Live Science.

Colossal scientists also focused on a gene that regulates fat metabolism and fatty acid absorption in mice. Woolly mammoths thrived in frigid temperatures in part thanks to fat deposits beneath their skin, so the team attempted to confer the same deposits onto mice by editing the associated DNA sequence.

But the effects of this insertion are unclear, Lynch said. "I guess they expected the mouse to have more or less body fat," he said, adding that the physical outcomes are likely too small to observe.

It's still unclear whether the genetically modified mice can tolerate colder conditions than standard mice, but Colossal scientists say they will test this in the coming months. "We know that the edits are in there, so now we just need to test what level of cold tolerance it confers," Lamm said.

While woolly mice are a step closer to the goal of bringing woolly mammoths back, there are still significant hurdles to overcome. For example, the technology involved in engineering the woolly mice is very advanced, but it's a far cry from what will be needed to get similar results in elephants, Lynch said. Mice have naturally dense hair, but that is not the case in elephants, meaning the technical challenge will be much greater, he said.

"Elephants have fur, but the density of the hair is much less than other mammals, so even if they could make those mutations in an Asian elephant [...] it's just going to be really sparse," Lynch said. "So what you need to do, actually, is a bunch of additional genome editing to somehow find a way to increase the density of the hair."

So why do cats really make this weird "stink face?" Turns out it has nothing to do with unpleasant odors — it's actually a sign that they're analyzing chemical signals in their environment.

Many animals, including wild and domestic cats, release pheromones — chemical signals used for communication between members of the same species. To detect and decipher these invisible messages, our feline friends rely on a special sensory organ in the roof of their mouths called the vomeronasal organ or "Jacobson's organ."

This organ is separate from the olfactory system (i.e. the nose), which detects odors but not pheromones, Alex Taylor, cat wellbeing and behavior advisor at International Cat Care, told Live Science in an email.

When a cat encounters pheromones, it processes them differently from odors. The cat instinctively opens its mouth slightly, lips curled back, displaying a behavior called the "Flehmen response." This expression makes it easier for pheromone molecules to reach the vomeronasal organ, enhancing the cat's ability to sense important chemical cues.

"This can look like the cat is grimacing, but there is no emotional aspect to this behaviour – the cat is just detecting and processing pheromones," Taylor said.

Related: Why do cats 'chatter'?

Cats use pheromones to communicate various messages: they can use them to mark territory without engaging in fighting or to strengthen the bond between mothers and kittens, Taylor explained. Pheromones also convey information about sexual status, indicating when a cat is in heat, said Mikel Delgado, a senior research scientist at Purdue University Veterinary College of Medicine in Indiana.

Pheromones are secreted by specialized glands located in multiple areas around a cat's body, including the chin, cheeks, the space between eyes and ears, edges of the lips, base of the tail, around the genitals and anus, between the paws and between the teats, Taylor said.

When cats rub their faces on furniture, scratch surfaces, spray urine or defecate, they leave behind chemical messages for other cats, Delgado told Live Science in an email. Later, other cats use their vomeronasal organ to analyze these scent marks and gather information about their feline neighbors.

During the Flehmen response, pheromone molecules enter a cat's mouth — either through licking or inhalation — and dissolve in saliva. They then travel through two passages in the roof of the mouth, known as the nasopalatine ducts, which lead to the pair of fluid-filled sacs that make up the vomeronasal organ, Taylor said.

When pheromone molecules reach the vomeronasal organ, they trigger nerve signals that travel to specific areas of the brain, namely the amygdala region of the hypothalamus and a region that controls sexual, feeding and social behaviors, Taylor said. In this way, chemical cues picked up by the vomeronasal organ directly influence a cat's behavior.

Unlike odors, the meaning of which is learned and can change with new experiences, pheromones trigger instinctive responses. A cat doesn't need to "learn" what a pheromone means — the knowledge is hardwired into its biology, Taylor said. While responses to pheromones are automatic, they can still be influenced by factors such as a cat’s development, surroundings, past experiences, and internal state like hormone levels, according to a review published in the Journal of Comparative Physiology A.

The vomeronasal organ isn't unique to cats. A range of animals, everything from rodents to reptiles, also use this second sense of smell to detect pheromones.

"The advantage of the Jacobson's organ is that animals can detect a wider range of molecules in the environment than animals lacking that organ," Jonathan Losos, an evolutionary biologist at Washington University in St. Louis, told Live Science in an email.

"Dogs are famous for their keen sense of smell, but that refers to their capabilities in their nasal passage," Losos said. "Cats have three times as many different types of scent detectors in the Jacobson's organ as dogs, which leads some experts to suggest that, overall, cat sense of smell may be comparable to that of dogs."

An evolutionary remnant of the vomeronasal organ, is even found in humans within the nasal septum, but there's no strong evidence that this vestigial version plays a role in chemical communication today.

For cats however, the vomeronasal organ is a powerful tool that enables them to interpret important social information in their environment. To quote Scottish novelist and poet Sir Walter Scott: "Cats are a mysterious kind of folk. There is more passing in their minds than we are aware of."

Where it lives: Movile Cave, southeastern Romania

What it eats: Insects, spiders and smaller centipedes

Why it's awesome: This deadly, yellow centipede has evolved to live in the Movile Cave — a pitch black, sulfurous underground system untouched by sunlight for more than 5 million years.

Discovered in 2020, Cryptops speleorex — meaning "king of the cave" — sits at the top of the food chain in the unique ecosystem. It is the largest invertebrate species in the cave, growing to between 1.8 and 2 inches (46 to 52 millimeters) long.

The centipede has adapted to life in complete darkness. Unlike its surface-dwelling cousins, C. speleorex has no eyes. Instead, it relies on other senses to track down prey, such as its long antennae that are highly sensitive to touch. These antennae help it detect vibrations and movements of prey in its environment. With its long, spidery legs, the king of the cave can navigate tight spaces with ease. The centipede has venomous pincers called forcipules that are designed to catch and immobilize prey once it gets close.

To survive in an environment that has no sunlight — and therefore no plants that produce energy via photosynthesis — the creatures in the cave depend on nutrients produced by bacteria through the oxidation of gases like methane and sulfur. This process is called chemosynthesis. C. speleorex then eats other creatures in the cave to gain these nutrients.

The king of the cave also has to contend with the array of deadly gases in its home. The Movile Cave is abundant in hydrogen sulfide, methane, ammonia and carbon dioxide, while it has around half the normal level of oxygen in the air outside the system.

It’s not known exactly how they have adapted to survive these gases. However, C. speleorex breathes through spiracles connected to a tracheal system that may have evolved to efficiently extract oxygen in low-oxygen environments.

While some species found in the cave also exist outside of it — such as microscopic roundworms called nematodes (Nematoda) — C. speleorex does not leave its inhospitable home, according to the researchers who discovered it.

"Our results confirmed our doubts and revealed that the Movile centipede is morphologically and genetically different, suggesting that it has been evolving from its closest surface-dwelling relative over the course of millions of years into an entirely new taxon that is better adapted to life in the never-ending darkness," the researchers said in a statement at the time.

According to a new paper published Friday (Feb. 28) in the journal Frontiers in Veterinary Science, scientists have discovered microRNA — small pieces of genetic information that play a crucial role in switching genes on and off — from bamboo lurking in pandas' blood. They say that this microRNA, or miRNA, may influence the expression of genes affecting the pandas' smell, taste and dopamine pathways.

“We showed that plant-derived miRNAs are present in the blood of giant pandas,” Feng Li, a researcher at China West Normal University, said in a statement.

“Our study proved that bamboo used as food for giant pandas does affect the change of giant pandas’ feeding habits.”

When pandas eat their bamboo diet, they absorb small pieces of genetic material from the bamboo into their bodies, just like we do with the plants we eat.

RNA is a single-stranded molecule made of the same molecular letters as our DNA. DNA, meanwhile, is a two-stranded instruction manual which consists of individual genes that tell our cells how to make specific proteins. miRNA are tiny scraps of RNA that can influence whether these genes are turned on or off, and how much of their products should be made, Li told Live Science in an email.

In the new study, Li and colleagues describe how they analyzed the blood from seven pandas, one of which was a juvenile, and found the presence of 57 miRNAs likely originating from their bamboo diet.

Related: Giant panda babies are born 'undercooked' and no one knows why

The researchers found that these miRNAs influenced the expression of genes related to the pandas’ feeding habits, including taste and smell signaling, digestion and dopamine pathways “which make certain activities, like eating fatty and sugary food or having sex, feel enjoyable). This indicates that these bamboo miRNAs may have influenced the food preferences of pandas, helping them find eating bamboo more appealing, and making them more suited to a life eating nearly nothing but bamboo.

“Bamboo miRNAs are not just dietary remnants but active regulators enabling giant pandas to thrive on an unlikely diet, bridging the gap between their carnivorous ancestry and herbivorous lifestyle,” Li told Live Science.

Additionally, the miRNAs were found to influence the ability of the pandas to sniff out fresh bamboo, and also helped them to absorb more calories from the nutrient-poor bamboo into their digestive system.

The discovery that miRNA from plants can have such an impact on the gene expression of animals could pave the way to a variety of treatments for both animals and humans alike, ”with “potential biomedical applications for treating inflammation and metabolic disorders,” Li explained. Previous research has also found that miRNA from the plants we eat can affect gene expression in humans and other mammals, potentially playing a role in regulating immune activity and, according to Li, "enhancing animals’ disease resistance.”.

Li and his team hope to extend the research beyond the seven pandas involved in their study to investigate the wider prevalence and impact of these molecules. “The giant panda is a very precious national treasure in our country, and blood samples are not easy to get,” Li said. “If possible, we hope to collect blood samples of young pandas who have not yet eaten bamboo for research, and perhaps get more surprising results.”

Researchers have captured extremely rare footage of polar bear cubs leaving their snowy dens for the first time.

The footage, taken on the Norwegian archipelago Svalbard, shows a mother polar bear (Ursus maritimus) plodding through the Arctic island's frozen landscape and her three cubs emerging one after another from a hole in the ice, before slipping and sliding around the frozen terrain.

The scene is from one of 13 den sites on Svalbard that scientists have been monitoring for nearly a decade to shed light on denning behavior, which is notoriously difficult to study because polar bear moms build the dens underground in hard-to-access areas.

The researchers described new aspects of denning behavior in a paper published Thursday (Feb. 27) in The Journal of Wildlife Management.

"It's a pretty special thing to see polar bear cubs emerge into this vast, white landscape that appears so inhospitable," lead author Louise Archer, a Polar Bears International postdoctoral fellow at the University of Toronto Scarborough, told Live Science in an email.

Related: Polar bears are getting horrific injuries and huge 'ice balls' on their paws because of climate change, researchers say

"In Svalbard, polar bears build their dens on the slopes of steep mountainous areas, and it's hard to imagine how cubs could find their feet in this severe terrain," Archer said. "Watching them sliding, tumbling, and even climbing up on their mother was truly remarkable."

The new study offers a glimpse at one of the most vulnerable and critical periods of a polar bear's life, researchers said in a statement.

Polar bears spend the winter in their dens. Pregnant females give birth around early January and nurse their cubs through spring, when the family emerges to slowly make its way to the sea ice. Newborn polar bears are hairless and weigh just 1 pound (0.5 kilograms). However, they grow quickly thanks to their mother's fatty milk and reach 22 pounds (10 kg) by the time they emerge as cubs.

Maintaining healthy polar bear populations depends on cubs' survival, which is only around 50%, according to the statement. Cubs survive only if their dens remain undisturbed throughout the winter and they can roam the surrounding area after emerging. Human activity jeopardizes both of these requirements.

"Polar bear mothers are having increasing difficulties reproducing due to climate-driven changes, and are likely to face further challenges with the expansion of the human footprint in the Arctic," Archer said in the statement.

To assess human influence on polar bear reproduction, researchers need to better understand denning behaviors and timings. A decade ago, Archer and colleagues fitted 13 female bears with GPS collars that recorded the animals' locations, body temperatures and levels of activity. The researchers used this data to locate the bears' dens, before traveling to Svalbard to install camera traps outside them.

The study is the first to combine collar data with camera footage of polar bears. "Every den we monitored had its own story," Archer said.

Throughout the study period, the moms and cubs first emerged in early March, sometimes venturing out for just a few minutes before returning to their dens. The families abandoned their hideouts earlier than previously recorded on Svalbard, but more observations are needed to confirm if this is a new trend, according to the statement.

The bears remained near their dens for an average of 12 days before heading off toward the sea ice, where mothers teach their cubs to hunt. The cubs stayed with their moms 95% of the time, rarely leaving the den alone. On Svalbard, cubs remain with their mother for 2.5 years after birth, according to the statement.

The researchers couldn't follow the bears once they left the den site. "I would love to know how the polar bear families we monitored fared once they departed the den," Archer told Live Science by email. "How soon does the mother catch a seal, [and] do her cubs manage to survive those initial few weeks when they venture out on the sea ice?"

Polar bears are currently snuggled up their dens, but it won't be long before they emerge again. Archer and colleagues are in Svalbard now, collecting information that may help them fill these gaps.

"We're excited to introduce new tools to monitor bears during this vulnerable time and to gain insight into their behavior across the Arctic," Archer said in the statement.

Megaraptorids were a group of fearsome predators in the Cretaceous period (145 million to 66 million years ago). They lived in the ecosystems of Australia and South America, which were joined together via Antarctica as part of a massive southern landmass called Gondwana.

Study lead-author Jake Kotevski, a paleontology doctoral candidate at the Museums Victoria Research Institute and Monash University in Australia, described megaraptorids as a "hands first predator" with muscular forearms and long, curved claws for catching prey — they effectively bring their prey in for a "hug of death," he said in a video released by Museums Victoria.

The fossils discovered by Kotevski and his colleagues belonged to an unspecified 120 million-year-old megaraptorid that was 20 to 23 feet (6 to 7 meters) long — making it one of the largest theropods (a bipedal group of mostly meat-eating dinosaurs) ever discovered in Australia. It also predates megaraptorids in South America by around 30 million years.

In the new study, published Feb. 19 in the Journal of Vertebrate Paleontology, researchers also identified fossils from another group of large, predatory dinosaurs called Carcharodontosauria, which are also found in South America but have never been identified in Australia before.

The carcharodontosaur fossils suggest that in Australia, these dinosaurs grew up to 13 feet (4 m) long, which is significantly shorter than their counterparts in South America, which grew up to 43 feet (13 m).

In other words, the roles of the two predatory dinosaurs seem to have been reversed in Victoria, with megaraptorids acting as the larger apex predators and carcharodontosaurs acting as smaller, secondary predators. Australia's unique Cretaceous ecosystem therefore had an "upside-down" dynamic, according to a statement released by Museums Victoria.

Related: What if a giant asteroid had not wiped out the dinosaurs?

The newly identified fossils were found in what were the banks of a large river, like the modern-day Ganges or Amazon, Kotevski told Live Science in an email. Southern Australia was close enough to the South Pole that it was within the Antarctic Circle during the Cretaceous, although the region was much warmer then than it is today.

The team identified the fossils, collected from the upper Strzelecki rock formation on the coastline of Victoria in southern Australia between 1988 and 2022, with modern 3D imaging techniques, including micro-computed tomography. The technique involves taking X-rays of an object as it rotates 360 degrees so that it can be studied in greater detail.

The fossils revealed that giant megaraptorids and carcharodontosaurs were living near the river, which Kotevski said was situated within a vast rift valley created as Australia pulled away from Tasmania and Antarctica.

"In the Antarctic circle, it has been proposed that Cretaceous [Victoria] experienced long periods of dark/light that the poles experience today," Kotevski said. "Thick forests lined this fast flowing river, where [a] myriad [of] small dinosaurs thrived, seemingly dominated by our … apex predator megaraptorid."

The discoveries add to evidence that dinosaurs were traveling across Antarctica to move between South America and Australia during the middle of the Cretaceous, according to the study. However, Kotevski noted that researchers still have a lot more to learn about the Australian dinosaur ecosystem.

"More discovery, collection and research is fundamental to further unlocking these secrets and building a picture of how these animals looked, differed, and behaved within their environment," Kotevski said.