December 2024

In 2020, prospectors hunting for ancient mammoth tusks in Siberia made a surprise discovery. The frozen clump of hair they noticed sticking out of a riverbank turned out to be a literal and figurative furball: a saber-toothed cat cub, desiccated and preserved in permafrost. Last month, scientists reported on their research on this first-of-its-kind specimen. The 37,000-year-old kitten mummy, complete with whiskers, fur, and claws, died when it was three weeks old. While the remains have not yet revealed how this individual cat died, they are providing insight into saber-toothed cats in general, including details that are hard to glean from bones alone. For example, the preserved kitten’s fur was dark brown, not spotted, as in many modern big cats, its neck was unusually thick and muscly, and its long upper lip might suggest that its famous canines would have been covered as an adult. Read on to learn more about the evolution of this charismatic group of mammals.

Where's the evolution?

This spectacular discovery prompted us at Understanding Evolution to dig deeper into the evolutionary history of saber-toothed cats. If you’ve got questions about the evolution of this iconic ice age predator, we’ve got (at least some) answers:

Was the mummified kitten a saber-toothed tiger? For that matter, was the saber-toothed tiger a tiger?

No and no. The mummified kitten was a member of the species Homotherium latidens and the saber-toothed tigers are Smilodon gracilis, Smilodon fatalis, and Smilodon populator. In fact, biologists have identified more than 50 species of saber-toothed cats which vary in size, body shape, tooth length, and more – and none of these cats are tigers!

In biology, organisms are classified according to their evolutionary history, which can be represented as an evolutionary tree, or phylogeny. A branch on the phylogeny forms a clade – that is, a group made up of all the organisms descended from a single shared ancestor. Clades (or branches of the evolutionary tree) form biological groups that can be named. For example, the cat branch of the tree of life has been given the name Felidae. The saber-toothed cats form a clade called the Machairodontinae. Since Machairodontinae is a twig on the cat branch of the tree of life, saber-toothed cats are, indeed, cats. However, the Panthera (the clade to which modern tigers, lions, leopards, and jaguars belong) is a completely distinct twig from the Machairodontinae, though one that’s also on the cat branch. So saber-toothed tigers (Smilodon) are not tigers, but they are cats!

What are saber-toothed cats closest living relatives?

Saber-toothed cats are equally closely related to all living cats – they are first cousins of both tigers and house cats. Biologists generally assess the closeness of an evolutionary relationship by evaluating how recently they shared a common ancestor. The more recent your common ancestor, the more closely related you are. Take a look at the phylogeny above. Trace your fingers down the house cat and Smilodon lineages. They meet at the common ancestor of living cats and saber-toothed cats. Now trace your fingers down the tiger and Homotherium lineages. They meet at that same shared ancestor. Any saber-toothed cat is equally closely related to all living cats. Furthermore, all living cats are more closely related to each other than any is to a saber-toothed cat. Trace your fingers down the tiger and housecat lineages. They share a more recent ancestor than either does with saber-toothed cats – and so are more closely related to each other than either is to saber-tooths.

How did saber-toothed cats use those teeth?

Scientists mainly agree that saber-toothed cats must have used their impressive teeth to kill their prey, but they still debate the details. Did the cats use their teeth to shear the neck of their prey and wait for the animal to die? Did they hold on to the neck and suffocate their prey, much as modern big cats do? Did their teeth somehow puncture key blood vessels? Or did they use their sabers on some other part of the prey’s body? Why didn’t their teeth break more often? How much did they scavenge, as opposed to actively hunting? Complicating matters, both jaw strength and tooth size and shape vary among saber-toothed cats, suggesting that different species may have used different strategies.

Were saber-toothed cats social, like lions are today?

Scientists aren’t sure about this one, and again, different species of saber-toothed cats might have had different behaviors. A couple lines of evidence suggest that at least some saber-toothed cats were social and, hence, might have hunted in groups. First, paleontologists have unearthed many examples of saber-toothed cat fossils with healed injuries. In modern animals, solitary predators who get hurt (e.g., fracture a bone) generally die soon after because they can’t hunt and get food. However, injured social predators can often survive and heal because their packmates provide food to the injured animal. Another line of circumstantial evidence comes from Friesenhahn Cave in Texas, where scientists have discovered several very young Homotherium and many older adults, but no intermediate ages. This might suggest that the cave was used as a den for a social group, in which juveniles left the cave to follow the adults out hunting, while the youngest members of the group stayed behind.

When and where did saber-toothed cats live?

The earliest saber-toothed cat fossils date to around 14 million years ago, and the last of these cats went extinct at the end of the last ice age around 11,000 years ago. They lived in Africa, Europe, Asia, and North and South America.

Did humans hunt saber-toothed cats? Did saber-toothed cats hunt humans?

Some popular, fictional accounts of prehistoric life imagine early humans living alongside dinosaurs and saber-toothed cats (we’re looking at you, Flintstones!). Of course, non-avian dinosaurs actually went extinct millions of years before humans evolved. But the same is not true of saber-toothed cats. Modern, tool-wielding humans would have encountered saber-toothed cat lineages both within Africa and as human populations migrated out of Africa and around the world. Our early human relatives like neanderthals and Denisovans also coexisted with saber-toothed cats. Since humans and saber-toothed cats overlapped extensively in time and space, and both hunted large mammals, clashes and competition seem likely, particularly the possibility that they scavenged off one another’s kills. However, clear and direct evidence of violent interactions between these two groups is minimal.

When and why did saber-toothed cats go extinct?

There are many different saber-toothed cat lineages, and these lineages went extinct at different times. This phylogeny shows the time periods that different species existed and when they likely speciated. You can see that the Nimravides lineage stops (i.e., went extinct) about 10 million years ago, while Smilodon and Homotherium went extinct quite recently in geologic time. These last two groups of saber-toothed cats survived until around 11,000 years ago in the Americas. They went extinct at the same time as many other large mammals in the Americas. Scientists are actively investigating several potential causes of this mass extinction, but many of these hypotheses involve climate change (Earth was heating up then, as it is now – though for very different reasons) and human activity (e.g., overhunting game, starting fires, etc.).

While saber-toothed cat fossils are relatively abundant – more than 2000 Smilodon are represented in California’s La Brea Tar Pits alone – we still have a lot to learn about their evolution and history. Why did different lineages go extinct? How did they hunt and kill? What sort of behaviors did they have? Were they social or solitary? New finds like the saber-toothed kitten, with soft body parts preserved, could shed light on these areas of uncertainty. And more of these discoveries will likely be made as the climate warms, and permafrost and glaciers continue to melt.