For just over 4 million years, planet Earth was home to what might be the ultimate cat.

It ranged from Africa to Eurasia and into the Americas through the Pliocene and Pleistocene epochs, making it the most successful big cat of all time.

Its name was Homotherium, aka the scimitar-toothed cat, and its secret was a unique combination of traits.

It was built like a hyena, it was highly social like a lion, and it chased down prey over long distances like a wolf.

But how did Homotherium evolve to be so successful and so different from basically all other cats, living and extinct?

Well the answer may lie in a huge geological event: the rise of the Tibetan plateau.

The cats we know and love today, from little to large, make up just a small fraction of the total cat diversity that once existed on our planet.

In fact, the lineage that includes all modern cats and their close extinct relatives once had a sister-group that’s now totally gone a sub-family known as the machairodonts.

Machairodonts diverged from the ancestors of modern cats around 23 million years ago.

For context, that’s about one-and-a-half times as far back as when housecats and tigers diverged.

And you might have heard of this group’s most famous member before: a sabertooth cat called Smilodon fatalis.

Smilodon earned its fame as the poster child of the machairodonts not just by being, well, incredibly metal, but also by leaving over 100,000 fossils behind Mostly in the La Brea tar pits of Los Angeles, leading to it be crowned the state fossil of California.

But while Smilodon tends to get most of the attention, another machairodont was arguably far more successful and impressive: Homotherium.

Because while Smilodon seems to have been confined to just the Americas, Homotherium conquered not only those continents, but most of the rest of the world, too.

After first evolving a little over 4 million years ago in the early Pliocene, Homotherium quickly spread everywhere, from the American West, to Northern Europe, to Southern Africa, to Eastern Asia.

This vast global range was the greatest of any wild cat before or since, and something that few species of mammals have ever managed without human help.

And while its fossil record is far more fragmentary than Smilodons’, the remains we do have suggest that Homotherium’s staggering success may have stemmed from its unique way of being a cat.

See, most cats from living species to extinct ones like the machairodonts have pretty similar behaviors and lifestyles.

They’re generally ambush predators that sneak up on unsuspecting prey and kill them in short, explosive bursts of speed.

Think of a jaguar pouncing from a tree, or a cheetah sprinting across a plain.

And they’re generally solitary too, with the exception of lions who live and hunt in prides.

All other cats prefer to hunt either alone or occasionally in small, temporary groups of just a few individuals at most.

But Homotherium seems to have bucked both of these trends with a different set of adaptations.

Some of these are clear from its fossils.

Homotherium had a strange, hyena-like build, with a disproportionately long neck and forelimbs, short hindlimbs, a sloping back, and a stubby tail.

These traits suggest that, rather than being adapted for short bursts of speed, Homotherium specialized in moving at moderate speeds across great distances.

It was a pursuit predator built for endurance, chasing down prey to the point of exhaustion.

And its claws were relatively small and built for running rather than grappling, suggesting that it would have needed to work in groups to hold down its large prey and deliver a killing blow.

More evidence of Homotherium’s unique lifestyle and behavior can also be seen at the molecular level, written into its DNA.

In 2020 for example, researchers published a study of its genome, reconstructed from ancient DNA from a fossil found in Canadian permafrost, dating back more than 47,000 years.

They found evidence of genomic adaptations for daytime activity, which is unusual for cats, who are generally most active at twilight or nighttime.

Plus, there were signs of positive selection on genes involved in breathing and blood flow, probably supporting Homotherium’s high endurance as a long-distance pursuit predator.

The researchers even found evidence of adaptations associated with both brains and behavior, which may have enabled the complex social interactions necessary to live and hunt in groups.

But we're still left with the question of why Homotherium evolved this way.

This strange and unique way of living must have emerged in response to strange and unique circumstances, after all.

The problem was that fossils of Homotherium’s early days are few and far between.

So we didn’t know what ecological conditions actually forged the ultimate cat, and why they haven’t pushed any other cats in quite the same direction or to such global success since then.

But that all changed in 2023, when scientists reported the discovery of a fossil of an early close relative of Homotherium, dating back nearly 10 million years.

It was a skull of a cat called Amphimachairodus hezhengensis that had lived on the northeastern border of the Tibetan Plateau during the Miocene Epoch.

And it seemed to suggest not only that this was where Homotherium’s ancestral lineage originated, but also that's where its weird mix of traits did, too.

Because A. hezhengensis already seemed to be Homotherium-like in lifestyle and behavior, potentially making it the pioneer of this peculiar way of being a cat.

Like, for example, its side eyes.

Having eyes positioned more towards the side of the skull gave it a wider field of view.

This is ideal for both identifying prey in open landscapes, and keeping track of the pals that they were coordinating their hunt with.

It’s something we see in lions, too but it was even more pronounced in A. hezhengensis.

And it’s distinct from earlier species in this lineage, like Machairodus, which had a range of view more like a tiger narrower, and specialized for being a solitary ambush predator hunting in closed environments like forests.

Plus, A. hezhengensis shared Homotherium’s distinctive wide forehead, which would have meant enlarged sinuses great for efficient breathing while running long distances.

And what's more, the researchers also analyzed an Amphimachairodus forepaw found nearby that showed signs of a healed injury.

Seeing as a cat with an injured paw would have probably been unable to hunt for itself, the fact that it survived long enough to heal suggests that it was part of a social group that cared for it.

And it probably wasn’t a coincidence that this major physical and social transition occurred on the Tibetan Plateau Because this might have been the perfect time and place to create the ultimate cat.

The Tibetan Plateau is the result of one of the most monumental geological events of the time the collision of India and Eurasia.

This created both the world’s tallest and one of its longest mountain ranges, the Himalayas, and the world’s highest and largest plateau.

This elevated highland stretches more than 2,500 kilometers from east to west and averages about 6 kilometers above sea level.

And when the Tibetan Plateau reached its current height around 10 million years ago, the environment shifted drastically in response.

Closed forested environments were replaced by more open, drier ones.

Conditions rapidly became so different that the region formed a sort of evolutionary hub, encouraging the development of new traits and behaviors in response.

Suddenly, being a short-distance ambush predator wasn’t a great strategy anymore.

Prey could see you coming from a mile away, and had plenty of escape routes to flee.

Instead, the environment favored predators with the endurance and stamina to chase prey down over long distances and the sociality to work as a team while doing so.

Plus, A. hezhengensis was far from the only carnivore in its environment.

It shared this part of the plateau with a huge and abundant bone-crushing hyena called Dinocrocuta gigantea arguably the ultimate member of its own family.

There were also large bears that seem to have had a bone-cracking diet.

With neighbors like this, being solitary like almost all other cats may have simply been too dangerous.

Especially seeing as in the new, open environments, there were few places to hide both their prey and their competition were almost always in view.

****So their solution might have simply been to trade stealth for stamina, and find strength and safety in numbers.

This was arguably one of the most important transitions in the entire evolutionary history of the machairodonts a moment when a lineage of cats broke all the usual rules.

And using the new strategy that its ancient relatives evolved on the Tibetan plateau, Homotherium eventually took over similar open environments.

As Earth’s climate gradually became cooler and drier throughout the Pliocene, those environments continued to spread across the globe, taking Homotherium along with them.

While we know that geology shapes environments, and that environments shape the species that live in them, it’s rare to be able to trace something as specific as a social life of a cat directly back to an ancient tectonic collision.

But without the ecological pressures caused by the geologic uplift, the ancestors of Homotherium might never have been forced to experiment with a new way of life And the ultimate cat might never have evolved at all.

So if Homotherium found such incredible success with its unique lifestyle, what happened to it?

Well, we still don’t know for sure.

After about four million years of roaming open grasslands, savannas, steppes, and tundras around the world, Homotherium eventually died out at the end of the Pleistocene.

And it’s possible that their decline might have had something to do with the rise and global spread of a new apex predator with a similar ecological strategy around this time Another highly social, pack-living, pursuit predator with a habit of chasing down large prey over long distances across open environments: us.

Just as Homotherium was unique in its family, Homo sapiens is unique in our own in many of the same ways.

And perhaps this town just wasn’t big enough for both the ultimate cat and the ultimate primate.