10 Extinct Creatures That Aren’t What We Thought

The study of extinct creatures has a major hurdle. There is no living dinosaur to observe. No cave lion to tag and track. So, when their stories are pieced together from scattered bones, theories, and a dash of popular media, we don’t always get the real picture.

This list looks at times when new evidence emerged, and the truth wasn’t quite what we thought it was.

Some discoveries might disappoint movie fans—megalodon might not have looked like a gigantic great white shark. Others are delightfully quirky, like the tiny goat that grew more like a reptile than a mammal. These finds can also flip established historical narratives, such as the supposedly cow-killing bear that actually ate a largely plant-based diet.

Related: Ten Ancient Secrets from the Neanderthal World

10 Ancient Squirrels May Have Scavenged Mammoths and Big Cats

Squirrels have a dark side to their diet: They are not the strict vegetarians that some people think they are. At least one species, the Arctic ground squirrel, will even eat dead members of its own kind.

This happens mostly when the squirrels emerge from hibernation and desperately need calorie-dense food. Their diet is chiefly plant-based, but in such a hungry state, meat offers a fast way to recover from months without regular meals. If a hungry squirrel happens across roadkill, and it’s another Arctic ground squirrel, dinner might be served.

In 2026, scientists studied droppings recovered from ancient Arctic ground squirrel nests in the Yukon. Some of the samples dated back as far as 700,000 years, and their preserved environmental DNA provided a remarkable picture of the animals and plants that once surrounded the squirrels.

Tests revealed DNA from more than 200 plants, along with genetic traces from mammoths, bison, horses, hares, caribou, wolves, and big cats. The findings don’t prove that the squirrels ate every animal detected in the samples. Some DNA might have come from scavenged meat or bones, while other traces could have entered through cached plants or the surrounding environment. Still, the results raise the possibility that ancient Arctic ground squirrels occasionally scavenged some surprisingly large—and dangerous—animals.^[1]

9 Modern Lions and Cave Lions Interbred

The cave lion (Panthera spelaea) was one of the largest cats ever to live—significantly larger and more robust than a modern African lion. It ruled as an apex predator for millennia before vanishing around 14,000 years ago as the climate, available prey, and human presence changed near the end of the last Ice Age. But although cave lions are gone, recent research revealed that they occasionally interbred with modern lions.

Since one cat is an extinct Ice Age animal and the other can be seen on a safari drive, it’s forgivable to assume that the two species didn’t live at the same time. However, their populations overlapped and sporadically produced hybrid offspring.

Curiously, climate appears to have influenced when this happened. Under normal circumstances, their territories didn’t overlap much. Cave lions preferred the cold grasslands and tundra of northern Eurasia and northwestern North America, while modern lions generally remained farther south.

But during especially cold periods, tundra habitat extended south into areas occupied by modern lions. The cave lions apparently followed the cold, bringing the two species into greater contact. Genetic evidence suggests that interbreeding became more common during these glacial periods and declined again when the climate warmed and the cave lions retreated north.^[2]

8 T. Rex Parents May Have Been Less Attentive Than the Movies Suggest

In The Lost World: Jurassic Park (1997), the characters use an injured T. rex infant to lure its parents. Both adults pursue the humans, recover their youngster, and attack the research trailer with enough force to push it over a cliff.

Sure, this is fiction, but movies can influence how we see dinosaurs. If that scene reflected a 2026 study, audiences might have seen much smaller hatchlings—and parents that invested less energy in each individual offspring than the movie suggests.

When scientists scoured museum collections for T. rex hatchlings, they identified extremely rare fossils that had previously gone unrecognized. The hatchlings were approximately 30 inches (76 centimeters) long. They weighed around 5.5 pounds (2.5 kilograms), making them closer in size to a small dog than the hefty infant shown in the film. They were also precocial, meaning they could probably move and feed themselves soon after hatching. Wear on their teeth suggests they were already eating vertebrate prey.

The team estimated that a small adult T. rex might have laid approximately 20 eggs in a clutch, while the largest females might have produced around 30. This doesn’t prove that the parents ignored their young. However, such large clutches suggest they provided less care to each hatchling than modern birds and mammals generally do, although potentially more than turtles, lizards, and crocodilians. A kidnapped youngster might still have inspired a rescue—but perhaps not quite the rampage depicted in the movie.^[3]

7 New Evidence Vindicated Nanotyrannus

In 1942, a small tyrannosaur skull was found in Montana. When scientists described it in 1946, they identified the fossil as a species of Gorgosaurus. But in 1988, other researchers argued that it belonged to a distinct genus, which they called Nanotyrannus lancensis. The name means “dwarf tyrant,” while lancensis refers to the Lance Formation where it was discovered.

However, the strong resemblance to Tyrannosaurus rex made many experts dismiss Nanotyrannus in favor of a teenage T. rex. This eventually became the prevailing interpretation, although the debate never disappeared completely.

Then, a multi-institutional team took another look at the original skull. The researchers focused on a rarely studied bone in the throat called the ceratobranchial, part of the hyoid apparatus. By comparing its microscopic structure with the bones of living birds and crocodilians, along with those of other dinosaurs, they could estimate the animal’s skeletal maturity.

The growth patterns indicated that the animal was mature or nearly mature when it died. In other words, it wasn’t a juvenile T. rex with a great deal of growing left to do. The results, published in 2025, offered strong new evidence that Nanotyrannus really was a distinct, smaller tyrannosaur.

A grown T. rex could measure approximately 40 feet (12 meters) long. In comparison, Nanotyrannus reached around 18 feet (5.5 meters). While significantly smaller, it still would have been a fearsome predator during the Late Cretaceous.^[4]

6 A Giant Fossil Broke the Supposed Limit on Bony Fish

Bony fishes have skeletons composed primarily of bone rather than cartilage. The other major group, the cartilaginous fishes, includes sharks, rays, skates, and chimeras. Some cartilaginous fish can get enormous. Whale sharks, for example, can weigh several dozen tons. But where are the bony fish giants?

For years, scientists debated this question. About 95% of all living fish species belong to the bony group, but despite this sheer variety, most are relatively small. The heaviest reliably measured bony fish was a giant sunfish, Mola alexandrini, that weighed approximately 3 tons (2.7 metric tons). It sounds heavy, but next to a whale shark, it’s puny.

Some scientists proposed that bony fish couldn’t reach comparable sizes because they appeared to have higher metabolic requirements than their cartilaginous cousins. This trait might conflict with the lower tissue-oxygen levels associated with extreme body size. Under this hypothesis, bony fish remained relatively small to avoid a potentially deadly combination.

Other researchers disagreed. In 2018, a study of the prehistoric fish Leedsichthys problematicus challenged that supposed physiological limit. This Jurassic monster lived approximately 165 million years ago and could reach around 49 feet (15 meters) long. Clearly, bony fish were capable of growing to whale-shark proportions without suffocating under their own metabolic demands.

The discovery broke the supposed size limit but didn’t entirely solve the mystery. Scientists still don’t fully understand why no bony fish approaching the scale of Leedsichthys survives in the oceans today.^[5]

5 California’s Monstrous Grizzly Was Mostly a Myth

The last known California grizzly was killed in the early 1920s, and the final widely reported sighting occurred in 1924. By then, documents and newspaper articles had given the bears a bloodthirsty reputation, describing them as gigantic hypercarnivores that slaughtered livestock at every opportunity. As a result, they were hunted, trapped, and poisoned to extinction.

Research published in late 2023 examined preserved skulls, bones, and fur from California grizzlies to learn more about their behavior, diet, and size. The results were surprising. Historical accounts claimed that some California grizzlies weighed as much as 2,000 pounds (907 kilograms), but measurements of museum specimens suggested that the bears generally fell within the same size range as modern North American grizzlies. A representative California grizzly probably weighed closer to 440 pounds (200 kilograms).

Stable-isotope analysis of the preserved fur and bone also revealed that the bears were omnivores with largely plant-based diets. Before European colonization, meat contributed only around 9% of their diet. That proportion rose to as much as 26% after settlers introduced livestock and transformed the landscape.

The bears probably killed some cattle and other domestic animals. Still, the evidence suggests that historical accounts greatly exaggerated how often it happened. The monstrous, 2,000-pound cow killer wasn’t entirely invented—but it was far from the average California grizzly.^[6]

4 The “Dumb” Dodo Wasn’t So Dumb After All

The dodo (Raphus cucullatus) was a large, flightless pigeon from Mauritius. After the final widely accepted sighting in 1662, the bird disappeared and gradually acquired a reputation for being fat, slow, and stupid. But many researchers now believe the dodo got a bad rap.

A 2026 study focused on the birds’ brains to learn more about their intelligence and behavior. No preserved dodo brain exists, but researchers used CT scans of surviving skulls to create digital endocasts of the cavities that once held the brain. They then compared the reconstructed shape with the brains of living pigeons and doves.

The results were fascinating, suggesting that dodos behaved differently from most modern pigeons. The regions associated with smell were enlarged, while the optic lobes responsible for processing visual information were surprisingly small. This combination suggests that dodos may have been nocturnal or crepuscular, meaning they were most active at night or during twilight.

The reconstructed forebrain was proportionally similar to those of living pigeons, providing no evidence that the dodo was unusually stupid. Modern pigeons can learn to recognize words and images, distinguish quantities, and remember complex visual patterns. That doesn’t prove that dodos possessed all the same abilities, but it does show why having a pigeon-like brain is hardly evidence of stupidity.^[7]

3 Some Denisovans May Have Been Surprisingly Tall

For a long time, Denisovans were humanity’s most mysterious extinct cousins. Scientists first identified the archaic human lineage in 2010 through DNA recovered from a finger bone found in Siberia’s Denisova Cave. Subsequent discoveries, including teeth, jawbones, and skull fragments, provided a patchy picture of what they might have looked like from the neck up: robust humans with large teeth, heavy jaws, and pronounced browridges.

The rest of their bodies remained elusive. Then, researchers examined a partial shin bone and thigh bone recovered through commercial dredging in the Penghu Channel off Taiwan. Researchers recognized the bones as hominin remains around 2010, but a 2026 analysis identified them as Denisovan through preserved proteins.

Neither bone was complete, but the researchers estimated that the thigh bone belonged to an individual who stood around 5 feet 11 inches (1.8 meters) tall and weighed approximately 183 pounds (83 kilograms). The owner of the shin bone may have reached 6 feet 3 inches (1.9 meters) and weighed around 200 pounds (91 kilograms).

These individuals didn’t dwarf every other prehistoric human, but their bones rank among the largest known from any Pleistocene hominin. They also suggest that at least some Denisovans in eastern Asia were considerably taller and heavier than many other ancient populations in the region.

However, the bones were dredged from the seafloor rather than discovered in a securely dated archaeological layer, so their exact ages remain unknown. The protein analysis and height estimates were also released as a preprint that had not yet undergone peer review. Until more Denisovan skeletons appear, researchers cannot know whether these two individuals were typical of their population or simply unusually tall.^[8]

2 Megalodon May Have Been Longer and Leaner Than We Thought

Megalodon (Otodus megalodon) cruised the oceans between approximately 23 million and 3.6 million years ago. Most of its fossils are enormous teeth, although scientists have also discovered vertebrae and other pieces of calcified cartilage. Based on this limited evidence, they concluded that it was the largest shark ever to live.

In 2025, researchers reexamined one of the most complete known specimens: a partial vertebral column discovered in Belgium more than a century ago. The preserved trunk section measures approximately 36 feet (11 meters). To estimate the shark’s complete length, including its missing head and tail, the study compared body proportions across 165 living and extinct shark species.

The researchers calculated that the Belgian specimen may have reached around 54 feet (16.4 meters) long. They also examined images of much larger vertebrae found in Denmark. Scaling up from those bones produced a possible maximum length of 80 feet (24.3 meters). However, that figure remains a model-based upper estimate rather than the measured length of a complete animal.

While megalodon may have been bigger than many previous estimates, the real surprise was the shark’s proposed shape. Instead of resembling a supersized great white, it may have possessed a more elongated and slender body superficially comparable to that of a lemon shark.

This design would have made sense for such a massive predator. A thinner body would have reduced water resistance, lowering the energy required to move through the ocean. But without a complete skeleton or body outline, scientists still cannot know precisely what megalodon looked like. The familiar gigantic great white may be wrong, but its leaner replacement remains a carefully calculated reconstruction.^[9]

1 A Mammal with Reptile-Like Growth

Cold-blooded animals like reptiles rely heavily on external heat to regulate their body temperature. Warm-blooded species like mammals generate and regulate their own heat, although doing so requires a steady supply of energy. No living mammal is fully cold-blooded in the reptilian sense. But one extinct goat evolved a remarkably reptile-like way of conserving energy.

The Balearic Islands cave goat (Myotragus balearicus) stood roughly 17.7 inches (45 centimeters) tall at the shoulder. Its lineage survived on the resource-poor Mediterranean islands of Mallorca and Menorca for about 5.2 million years before disappearing several thousand years ago, around the time humans settled the islands.

The reason behind the goat’s sluggish growth became clearer in 2009 when researchers examined its bones. They discovered lamellar-zonal tissue and lines of arrested growth similar to patterns commonly associated with crocodilians and other reptiles. These features suggested that the goat could slow or temporarily stop growing when resources became scarce.

Most mammals maintain relatively fast, steady growth because their high metabolic rates require a steady energy supply. The cave goat followed a different strategy. Trapped on islands with limited food and few natural predators, it evolved unusually slow, flexible growth and reduced its energy requirements.

The animals may have taken around 12 years to reach their full size, far longer than modern goats. However, the bones cannot prove that the species was completely cold-blooded, and later researchers have questioned whether this type of tissue is truly unique among mammals. The safest conclusion is still a strange one: This tiny goat remained a warm-blooded mammal but grew more like a crocodile.^[10]