The Evolution of Cats: 5. Sabertooths, Part 1

A multi-million-year predator niche has been empty for the last 11,000 years.

We should be celebrating that fact. Instead, we have forgotten the terror that these ferocious animals inspired in our ancestors.

We wish they were still around.

Well, it’s understandable. If safety could be guaranteed, who wouldn’t want to go see a live sabertoothed cat at the zoo?

If…

Paleontologists have gotten DNA from well-preserved fossils of the two most famous sabertooths – Smilodon and Homotherium. (Barnett and others)

But if Jurassic Park-style cloning really worked LINK, safety could not be guaranteed in the saber-cat enclosure.

Nobody knows how these extinct animals behaved.

Some of them were probably good jumpers (Morales and others); most could climb; and a few behemoths had the brutal momentum that a half-ton body mass makes possible when they charged. (Antón; Turner and Antón)

Anyway, they were all cats and therefore moody, quick to react, and unpredictable.

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A modern human would be eyeball-to-eyeball with Smilodon populator here.

Yet, despite the risks, we all so want to see a sabertoothed cat!

The idea of a living sabertooth isn’t total fantasy. It’s very unlikely, but a new one really could appear any day.

After all, evolution is still going on.

And for the last fifty million years (Antón), that ambush-and-slash niche for sabertoothed mammals has always been refilled after a brief vacancy. Then it has been occupied for tens of millions of years at a stretch.

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We could all go back to caves . . .


It’s good to be an apex predator.

Cats didn’t invent saberteeth. These killing tools go back to the days before mammals.

How did cats get them and why aren’t there any sabertooths around today?

Saberteeth

All cats are hypercarnivores. That’s why Fluffy the Housecat can’t live on dog food – it needs the special balance of protein and amino acids that canned and dry cat food contains.

In the wild, cats depend on prey animals. To survive, their canine teeth have evolved into fangs. (Holliday and Steppan; Kitchener and others)

Bengal tigers have the largest fangs of any modern cat – up to 4 inches (10 cm) long. (Heske, Lab 19)

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The fangs of this Brazilian jaguar along the Rio Negro are impressive, too.


In comparison, Smilodon’s saberteeth were almost a foot (28 cm) long. (van den Hoek Ostende and others) But those weren’t really fangs.

In today’s big cats, upper fangs are rather cone-shaped – thick at the base and tapering up into a point.

Saberteeth were much flatter, front to back, than the fangs of any “normal” modern cat. (Martin, 1980; van den Hoek Ostende and others)

The edges looked like knives. Indeed, the technical name for sabertoothed cats is Machairodontinae, which means “Knife-Tooths.” (Antón; Turner and others)

But appearances are deceptive. Saberteeth were actually blunter than a steel blade, although sometimes they were serrated. (Turner and Antón)

Mechanical experiments show that saberteeth could only cut through hide and animal tissues when the cat also made a slicing movement during its killing bite. (Wheeler)


Hence the name ambush-and-SLASH for a sabertoothed predator. In contrast, all modern cats use a stalk-and-pounce hunting technique. (Werdelin, 1989)

Paleontologists say that there are subtle differences in saberteeth between two major sabertoothed cat tribes, the Homotheriini and the Smilodontini.

Homotherium and its relatives were scimitar-toothed. Their saberteeth tended to be broad and very flat, with coarse serrations. (Antón; Martin, 1980)

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Homotherium


The Smilodontini were dirk-toothed cats. Their sabers were generally longer and straighter, less flattened, and with very fine serrations to none at all. (Antón; Martin, 1980)

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Smilodon populator was an extreme dirk-tooth.  

Per Antón, the species name “necator” isn’t used any more.

These subtle differences matter a lot to experts. That’s why you’ll often see “dirk-tooth” or “scimitar-tooth” on the Web or in books about sabertoothed cats.

But for general purposes, it’s still perfectly okay to just call them all sabertooths.

Sabertooths down through time


These specialized upper canine teeth aren’t all that unusual in fossil carnivores.

Since the K/T extinction sixty-five million years ago, at least four mammal groups have had them. (Kitchener and others)

All four, plus the very first sabertooths – those Permian gorgonopsids we met last time – are shown here, drawn to scale:

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That must be The Doctor. Only a Time Lord could get into such a predicament – millions of years actually separate some of these animals from the others.

The 250-million-year-old gorgons (Antón; Kemp) are red (a species from Russia) and pink/purple (from southern Africa).

The little critter wearing black is one of two known sabertoothed creodont species. Creodonts were among the first mammal predators after the K/T extinction. These sabertooths lived in North America early in the Paleocene geological epoch, when almost all mammals were still very small. (Antón; Hunt, 2004; Prothero, 2006)

The green sabertooth is a cat-like nimravid. We have met these animals in other posts; now they are waiting for us in the next section.

That medium-sized orange creature is Thylacosmilus – a roughly 3-million-year-old South American marsupial sabertooth that probably went extinct shortly before the saber-cats moved in. (Antón)

This leaves Barbourofelis (light blue), who is also waiting for us below, and the two very famous cats already mentioned:

  • Homotherium (purple) first appeared in Eurasia about 6 Ma (million years ago) and in North America around 4 Ma. Werdelin and others) It went extinct about 10,000 years ago. (<Antón)
  • Smilodon (yellow) terrorized North and South America from the Pleistocene until roughly 13,000 years before the present. (Antón; Werdelin and others)

Nimravids, barbourofelids, and true cats

It’s more correct to say that Fluffy and Leo look like nimravids than to call nimravids cat-like, but very few people would know what you meant.

Nimravids are long gone and forgotten now, but they were the first really “catty” mammals ever.

About thirty million years after the K/T extinction, they bounded onto the scene in North America, possibly after crossing over the Bering land bridge from Asia. (Averianov and others; Bryant)

Nimravids were also the first known hypercarnivorous mammals of the post-K/T world. (Holliday and Steppan; Van Valkenburgh, 2007)

There were some skeletal differences, but these amazing groundbreatkers had the same basic feline body plan as Fluffy – long legs, retractable claws, and sharp teeth. (Bryant; Turner and Antón)

That’s why early paleontologists called them “paleofelids.” It seemed obvious that these animals were the ancestors of modern cats, i.e., “neofelids.” (Antón)

However, more discoveries have shown that, despite appearances, nimravids weren’t cats. (Antón; Averianov and others; Werdelin and others)

Very subtle cranial details show that they might even have been related to the dog family! (Flynn and Galiano; Prothero, 2006; Werdelin and others)

While paleontologists puzzle over this, it’s at least clear that the strong resemblance between nimravids and cats is a case of convergent evolution LINK. (Antón; Bryant; Werdelin and others)

The barbourofelids are more of a challenge.

Their heyday was in the Miocene, after the nimravids had vanished. (Van Valkenburgh, 1999; Werdelin and others)

Barbourofelids were also very cat-like. At first, everybody thought they were just a second wave of nimravids. (Bryant)

Then more study showed that barbourofelids weren’t related to the earlier nimravids.  Perhaps they were cats . . . perhaps not. Frankly, no one knows yet what they were. (Werdelin and others)

At this point in geologic time, there were both barbourofelids and true cats prowling through the forests and woodland savannas of Europe and North America. (Agustí and Antón; Prothero, 2006; Werdelin and others)

Apex predators during the first part of the Miocene had been caniforms LINK, but as the epoch progressed, feliform LINK hunters were beginning to make their presence felt. (Van Valkenburgh, 1999; Werdelin, 1989)

In Europe, the Pseudaelurus complex of true cats emerged around 20 Ma. North American pseudaelurines either evolved separately or else immigrated there from Asia around 17.5 Ma. (Rothwell; Werdelin and others)

Throughout the northern continents, these early cats ranged in size from a modern wildcat to a leopard. (Werdelin and others)

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Leopards aren’t as big as tigers or lions, but they’re still impressive – especially up close.  This is too close for either cat or human.

Then, late in the Miocene, pseudaelurines somehow evolved into both sabertoothed and modern cats. (Rothwell; Werdelin and others)

No direct fossil evidence shows how this happened, but at least two out of a total of eleven known species had to be involved. (Rothwell; Salesa and others, 2011; Turner and others; Werdelin and others)

While sabertooth DNA may not be useful for cloning, it does show that modern cats aren’t descended from Smilodon or Homotherium. (Barnett and others)

So modern cats and the sabertooths both belong in the cat family, but they represent two different lines.

Today’s cats, technically, are part of the the cat family’s Felinae subgroup. The sabertooths belonged to a sister subgroup – the Knife-Tooths.

Candidates for the Knife-Tooth ancestor include a roughly 70-pound (30-kilogram) Miocene cat that we’ll have to call Pseudaelurus quadridentatus because extinct animals don’t have common names. (Antón; Rothwell; Salesa and others; Turner and others; Werdelin and others)

P-Quad had somewhat flattened canines and a few other characteristics that remind paleontologists of sabertooths. (Antón; Turner and others)

Overall, though, P-Quad resembled a modern cat, with a short face, long back, and long hind legs for getting around in trees. (Turner and Antón)

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This modern margay cat has a very stable perch because its entire hindfoot is in contact with the branch. (Turner and Antón)

The pseudaelurines didn’t have long hindfoot bones like modern cats. Those came later, as cats’ feet began to stretch out to give them an extra edge in speed. (Turner and Antón)

P-Quad probably spent most of its time in trees (Antón), since dangerous predators like amphicyonids (sometimes called “beardogs”) owned the ground. (Hunt, 1989, 2004)

There wasn’t total safety in the forest canopy, though. Barbourofelids could climb, and they had reached the top of the food chain now.

To say that they had saberteeth is an understatement. The image at the top of this post is Barbourofelis fricki.

Not all barbourofelids were as extreme as that. (Werdelin and others) However, they were middle-Miocene Europe’s typical meat specialists (Agustí) – the position in the food web that modern cats now fill.

P-Quad and the other pseudaelurines just had to make the best of things for a while and quietly evolve.

And then, around 12 Ma, the first true sabertoothed cats finally appeared in western Eurasia and Africa. (Agustí; Turner and Antón; van den Hoek Ostende and others; Werdelin and others)

The First Sabertoothed Cats

The early history of the two major saber-cat tribes isn’t well understood yet. (Martin and others, 2011d; Werdelin and others)

Different paleontologists call the first sabertoothed cats by different names. (Antón; van den Hoek Ostende and others; Werdelin and others)

“This discussion is far from settled, but at the very least shows that these forms grade into one another.”
— Werdelin and others

The debatable names are “Miomachairodus,” “Machairodus,” and “Amphimachairodus.”

Another facet to the controversy is that many paleontologists – but not all of them – think that this group gave rise to Homotherium’s tribe.

When there is scientific uncertainty, a layperson should avoid the subject altogether, but that isn’t possible when talking about the earliest known sabertoothed cats.

While professional fossil-cat herders continue to debate the details and slowly reach a consensus, I have chosen two specific sources to follow.

Mauricio Antón calls those early sabertooths Macharoidus and describes Amphimachairodus as a separate group. (Antón)

And according to Werdelin and others, these are the ancestors – somehow – of Homotherium.

So that’s how I am going to describe it for now.

On a quick glance, someone time-traveling to the Mediterranean region as it was in 12 Ma might have mistaken Machairodus for one of today’s big cats.

Machairodus was generally built like a tiger, except for a very narrow face, a longer neck than any big cat has today, and a short tail. (Antón; Turner and Antón)

Machairodus also had saberteeth . . . and advanced ones at that. (Antón)

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Experts have painstakingly pieced Machairodus together from fossil fragments found in a natural carnivore trap near Madrid.

Those sabers are impressive, but they look a little strange to paleontologists. Perhaps “out of place” is a better way to put it.

The saberteeth are so advanced, they might have belonged to Homotherium, but Machairodus doesn’t have the rest of a sabertoothed cat’s features, like massive jaw muscles, powerful forelimbs, and a short hindlegs. (Antón)

In fact, this very feline animal had long back legs that probably made it quite a good jumper. (Antón; Turner and Antón)

Clearly the Homotheriini evolved saberteeth first and then worked out the rest later. Scientists call this process mosaic evolution. LINK (Antón)

Even without characteristics that would enhance the advantages of saberteeth, Machairodus thrived. (Antón)

Its earliest fossils come from Turkey and Africa. After that, this group of saber-cats spread out across both Eurasia and North America. (van den Hoek Ostende and others)

Machairodus was the first member of the cat family to reach the size of modern lions and tigers. One of its most successful species, M. aphanistus, was over 3 feet tall (100 cm) at the shoulder. (Antón)

Perhaps being big offset the lack of other sabertooth features.

Saberteeth allowed for a faster kill (Antón; Turner and others), and Machairodus could have gotten started on the same sized prey that today’s big cats handle. (Deng and others)

Over time, sabertooths became more efficient, developing other physical marks of a sabertooth. (van den Hoek Ostende and others)

They were ready to go after bigger prey, once they had the whole “sabertooth complex.” (Antón)

This included, but wasn’t limited to, powerful forelegs and shoulders to overpower prey and a long, muscular neck to safely position the sabers for that killing bite. (Antón; Turner and others)

Megaherbivores the size of junior mastodons that Homotherium would eventually tackle in the Pleistocene existed back in the Miocene (Antón; Agustí and Antón; Prothero, 2006), but they were probably safe from all of the early sabertooths. (Antón)

Machairodus followed smaller prey – zebra-sized migrating horses – out of central and western Asia into Europe, where it found lots of other suitable plant-eaters. (Agustí )

This sabertoothed cat coexisted with the barbourofelids (Agustí ; Antón) and held its own against Europe’s big amphicyonid beardogs and ursids (members of the bear family Ursidae). (Hunt, 1989)

Around 10 Ma, a more advanced sabertooth – Amphimachairodus – replaced Machairodus. (Antón)

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Amphimachairodus (bottom) and partial skull of Proailurus, the Dawn Cat (top). Some fifteen million years of evolution separate the two.

A-Mach was even bigger than Machairodus – almost 4 feet high (120 cm) at the shoulder – and its head was longer and narrower. (Turner and Antón)

This saber-cat also had a very muscular neck, as well as enormous dewclaws for holding onto prey animals like horses and antelope. (Antón)

However, A-Mach still overall looked like a modern cat. (Antón; Werdelin and others)
That is, it was still very primitive.

Today we tend to think the sabertooths were primitive because they went extinct. Actually, Homotherium and Smilodon were very advanced specialists. (Antón; Turner and Antón)

Today’s cats are the die-hard conservatives. No cat owner will be surprised by this, of course, but it shows up not only in mood but also in Fluffy’s build.

Modern felines still have the general Pseudaelurus body plan. They have just changed the legs and feet a bit to make it easier to move on the ground. (Antón; Turner and Antón)

Back in the late Miocene, there was a lot of ground to cover.

A “veritable freeway” for both predators and prey existed across the Bering land bridge between Eurasia and North America. (Prothero, 2006, including quote)

In addition, a tectonic collision between Africa and Eurasia had opened up routes between these two continents, as well.

The elephant family, whose members would eventually evolve into Ice-Age mastodons and mammoths, ventured out into the wider world while Eurasian sabertooths followed prey into Africa’s mosaic landscapes of forest and wooded grasslands. (Agustí and Antón; Strömberg)

Fossils of these African sabertoothed cats from as far back as 10-11 Ma are still being excavated and studied. (Antón; Peigné and others)

Perhaps the most impressive to date is Machairodus kabir, from Chad. This enormous saber-cat might have weighed 350-490 kilograms (770-1100 pounds)! (Peigné and others)

That’s plenty big enough to take down plant-eaters weighing close to a ton. (Peigné and others)

Another sabertooth, with the jaw-breaking name of Lokotunjailurus, has been found in both Chad and Kenya. The size of a modern lioness, it goes back to about 7 Ma. (Antón; de Bonis and others)

At first, paleontologists thought this long-limbed, graceful sabertoothed cat was Machairodus. However, further study showed that Lokotunjailurus was a separate species, with some similarities to Homotherium. (Antón; van den Hoek Ostende and others)

It’s too bad there are no common names for these beautiful animals. The scientific names are so long, especially in a family tree!

Some paleontologists, noted above (Werdelin and others), draw a very general family tree of the Homotheriini this way: Machairodus around 12 Ma, through Amphimachairodus at about 10 Ma, to Homotherium.

Perhaps Lokotunjailurus fits in there between Amphimachairodus and Homotherium. (van den Hoek Ostende and others)

According to phylogenetic computer analyses LINK, Homotherium first showed up in Europe around 6 Ma and then in North America two or three million years later. (Werdelin and others)

The oldest fossils go back to 4 Ma. They were found in both Africa and the Ukraine, which means that Homotherium could have evolved in either Eurasia or Africa. (Antón and others)

The roots of Smilodon’s tribe

Many cat fossils are still buried by time, waiting to be discovered. (Johnson and others)

Smilodon’s ancestors are among the missing. (Antón; Werdelin and others)

However, some possible early candidates have been recognized. There was Promegantereon, around 11 to 10 Ma. (Werdelin and others)

It was the size of a puma, with saberteeth that weren’t very long but were flat in cross-section, with a curve. (Salesa and others, 2010b)

Promegantereon was smaller than Machairodus, but it had some of the other sabertooth complex features, including powerful forelegs, a big dewclaw, and a narrow head. (Antón; Turner and Antón)

This saber-cat was still primitive, like Machairodus, but already it was built to wrestle down prey. (Salesa and others, 2010a)

Even early on, strength mattered in this group.

Promegantereon hunted deer, antelope (Turner and Antón), and other prey in Eurasia and Africa from about 10 Ma to 8 Ma. Then leopard-sized Paramachaerodus showed up around 8 Ma and held the ambush-and-slash niche for another three million years. (Salesa and others, 2010b)

Paramachaerodus had moderately long, serrated sabers. Its other sabertooth features were a little more developed than Promegantereon’s. (Salesa and others, 2010b; Turner and others)

Smaller saber-cats like these probably coexisted with lion-sized Amphimachairodus by sharing resources in some way that’s not well understood yet. (Werdelin and others)

Perhaps they took refuge in trees, just as modern leopards do today in lion and tiger country. (Antón; Domingo and others)

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Toward the end of the Miocene, Europe’s rich wildlife suffered a crisis that was probably related to global cooling. Barbourofelids and amphicyonid beardogs were among the casualties, but the Knife-Tooths came through it all right.(Agustí ; van den Hoek Ostende and others)

In the new Pliocene epoch, Paramachairodus was replaced by Megantereon – an undisputed member of the Smilodontini tribe. (Antón; Hunt, 2004; van den Hoek Ostende and others)

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Megantereon

This jaguar-sized saber-cat got around – ranging across Eurasia, Africa, and North America – but apart from the spectacular skeleton displayed above, few of its fossils have been discovered yet. (Antón; Zhu and others)

As a result, no one is sure when or where Megantereon evolved. (Antón; Zhu and others)

This matters a lot to paleontologists, because the most iconic sabertooth of all – Smilodon – appeared after Megantereon’s arrival.

Everybody, laypeople as well as scientists, wants to know where Smilodon came from.
Some experts think that Megantereon traveled into North America from Asia and evolved into Smilodon around 2.4 Ma. (Hunt, 2004)

There are other possibilities, for instance, that Smilodon and Megantereon were two groups, or that they and another saber-cat that its discoverers have named Rhizosmilodon shared a common ancestor. (Wallace and Hulbert)

It’s even possible that Megantereon was in Africa around the time of Lokotunjailurus, long before it appeared on other continents. (de Bonis and others)

But many people appreciate this saber-cat in its own right.

Mauricio Antón sums it up well when he writes:

Just as many naturalists consider the leopard to be the ultimate big cat, I find Megantereon to be the ultimate sabertooth . . . Megantereon struck a balance between strength and grace…Like the jaguar, it could explode out of concealment with lightning speed, and it was large enough to hunt big prey such as horses and deer but still agile enough to be a proficient climber.

Here we are at last, some two and a half million years before the present. The Miocene is far behind us, snow is beginning to fall, and vast areas of the continental polar regions are icing over. (Agustí and Antón)

The most advanced cats to ever walk this Earth – Homotherium, Megantereon, and Smilodon – are now well established and at their peak.

And we are at a crossroads.

There are two ways we can go next. The classical approach is to discuss the Homotheriini and Smilodontini tribes. We’re going to do this.

But there’s a problem with the tribal approach.

Antón counts a third tribe – the Metailurini – because they had some sabertooth features. However, Werdelin and others say that those cats are very hard to classify and calls the Metailurini “a waste-basket taxon.”

I think the Metailurini fit better into a discussion of the second approach, which is very new. It defines saber-cats differently and leads to some surprising conclusions about them (Christiansen) that we will look at next time.

The Homotheriini

Quite apart from the whole scimitar- and dirk-tooth thing mentioned earlier, the Homotheriini and Smilodontini were very different cats.

Homotherium species tended to be long-legged, like a modern lion. They were also rather lightly built compared to Smilodon. (Turner and Antón; Werdelin and others)

Homotherins still had the powerful forearm muscles needed to hold down and immobilize prey, of course, but their build wasn’t extremely massive (Werdelin and others), like Smilodon’s forelimb power-package.

Xenosmilus – another member of the Homotherini tribe – was the exception to the lion-legs rule.

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Xenosmilus

Xenosmilus hodsonae lived in what is now Florida around 1 Ma. (Antón)

This cat had the flat, coarsely serrated sabers of the Homotheriini, with an arc of big incisors and huge scissor-like cheek teeth for slicing meat. (Antón)

Some experts look at those incisors and lower canines and think that Xenosmilus used a different method to kill its prey, one that resembles the way sharks and piranhas attack today. (Naples and others, 2011; Wheeler)

However, this idea needs a lot more testing. (Wheeler)

The most obvious difference with Xenosmilus was that its legs were short and powerful – like those of the Smilodontini. (Antón)

One theory to explain these structural differences uses an idea called “ecomorphs.”
Evolution can work through an animal’s interactions with either its environment or the living beings around it. (Benton)

According to ecomorph theory, certain body types adapt to fit into specific environments. Generally speaking, the cat-like ecomorph goes with a habitat that has both open areas and trees. (Martin, 1989)

For example, pursuit carnivores tend to have long legs that help them conserve energy during the chase. (Andersson and Werdelin)

Since Homotherium generally had long legs, it may have been best adapted to open areas where it could chase prey, perhaps in a group. (Antón)

Xenosmilus, on the other hand, might have evolved when some homotherins moved into a more forested area, where ambush was a better way to hunt. Shorter, more powerful legs, like those of a modern jaguar, would be more useful here than speedy lion-legs. (Antón; Schellhorn and Sammgaraja)

This interesting theory hasn’t been proven yet, but it makes sense.

It also highlights just how much of the important information that we take for granted about modern cats – things like hunting behavior and socializing – can’t be found in fossils.

As we’ll see later, this makes it very difficult for scientists to understand why the sabertoothed cats went extinct.

Smilodon

There were three species of Smilodon, and they all lived in the New World.

The oldest one was S. gracilis. It was a sturdy sabertooth, the size of a modern jaguar, and resembled Megantereon, although its teeth and skeletal details were more specialized. (Antón)

Gracilis fossils have been found in the eastern and southern US, and as far away as South America. (Wallace and Hulbert)

Next came Smilodon fatalis. This is the movie star; the California state fossil; the Smilodon of Rancho la Brea tar pits. LINK (Antón)

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La Brea tar pits circa 1910

S. fatalis was as tall as a lion but much more of a hulk. A typical adult probably weighed up to 600 pounds (280 kilograms) or more. (Antón)

Its prey was big, too.  Over half of the plant-eaters studied at La Brea probably weighed more than 660 pounds (300 kg). (Van Valkenburgh and Hertel)

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Smilodon fatalis. Three cheers for those who painstakingly clean sticky tar off fragile fossils without destroying them!

Hundreds of these saber-cats died at La Brea, lured there by struggling animals caught in the tar and then getting trapped themselves. (Antón)

Their preserved bones have given investigators DNA, as we saw earlier. As well, the Fatalis skeletons provide an intriguing look into this cat’s lifestyle and some of the injuries it was prone to (Antón):

  • Smilodon didn’t break its saberteeth any more often than its other teeth, but all of the large carnivores at La Brea – wolves, lions, and coyotes, as well as cats – had more tooth fractures than modern ones do. (Van Valkenburgh and Hertel)
  • Smilodon repeatedly strained its shoulder muscles, probably while pulling in prey.
  • Chronic sternum injuries suggest that Smilodon smashed into prey chest first when it attacked. Yes, I’d like to see a video of that, too.
  • Pulled spinal muscles show how hard it was for even these big sabertooths to hold onto Ice-Age megafauna.
  • Leg and foot fractures probably happened accidentally or as the victim struggled.
  • Fights. One Smilodon skull has a hole in it the size of a Smilodon sabertooth; another saber-cat has a similar hole in its shoulder blade. (Antón) And one wolf skull has part of a Smilodon saber still embedded in its forehead. (Martin, 1980) We’ll never know if the victorious cat was able to survive with just one working sabertooth.

The hole in that one cat’s skull didn’t heal – it died of its wound. Usually, though, these skeletal signs of damage show some mending – the injured cats lived on for a while. (Antón)

One Smilodon broke its neck . . . and the fracture healed. (Rothschild and Martin)
This was one rugged cat!

Gracilis and Fatalis are the only species found in North America. (Antón)

But there is a third species known. It developed in South America, where an ambush-and-slash niche went vacant just before sabertoothed cats got there.

Back in the Miocene, North and South America had been separated by water. (Prothero, 2006)

During its isolation, South America had a sabertoothed marsupial predator, Thylacosmilus.

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Thylacosmilus got saberteeth through convergent evolution. It looks slightly different from the saber-cats because it was a marsupial – a completely different kind of mammal from nimravids, barbourofelids, and cats.

It’s not clear why Thylacosmilus went extinct, but the reasons may have involved climate change. (Antón; Turner and Antón)

Anyway, it just missed the arrival of northern saber-cats. (Antón; Turner and Antón)

Both Fatalis and Gracilis, as well as Homotherium and many other North American carnivores and plant-eaters, were able to cross over a land bridge – the Isthmus of Panama – starting around 2.7 Ma, when plate tectonics joined North and South America together. (Antón; Prothero, 2006)

There was plenty of room on the southern continent for Smilodon to evolve, and soon S. populator – one of the biggest sabertoothed mammals ever – appeared. (Antón; Turner and Antón)

The second name doesn’t mean that it was popular. “Populator,” according to sources in Antón, means “he who brings devastation.”

Fair enough for a cat 4 feet high at its incredibly muscular shoulder, good at leaping despite a weight of almost 900 pounds (400 kg), with paws bigger than any living cat’s, and saberteeth protruding half a foot (17 cm) below its jaw. (Antón; Turner and Antón)

If you have Antón’s book, check out Figure 3.67. It’s his illustration of Populator galloping across a field. He says it is based on a lion running.

I know cats move silently, but it’s hard to believe that the ground didn’t rumble and shake when this cat was in a hurry or when it collided with one of the gigantic Pleistocene plant-eaters during an attack.

Smilodon populator and the comparatively small S. fatalis from La Brea divided up South America between them during the closing millennia of the Pleistocene.

Populator thrived east of the Andes, from Venezuela to Patagonia, while Fatalis was an apex predator in the lands along the western coast. (Antón; Turner and Antón)

And so the world’s ambush-and-slash niche was occupied until roughly 10,000 years ago, when the last known Homotherium disappeared. (Antón)

By then, Smilodon had been gone for roughly 3,000 years. (Werdelin and others)

A great quiet did not descend upon the world when the saber-cats went away, because cats with “normal” upper canines were still around.

But ever since then, Earth has been missing something powerful and terribly beautiful.

Why did sabertoothed cats go extinct?

In the last post, we noted what all cats must do, 24/7/365, in order to exist as a living group of animals:

  • Use whatever resources are around, sharing or competing for them with other cats.
  • Hunt prey that is evolving rapidly and in a variety of ways.
  • Have sex and raise kittens.
  • Cope as best they can with other community predators.

Sabertoothed cats did all that for roughly 12 milion years. Somewhere in there are the keys to their early development, their greatest successes, and their eventual extinction.
As we have seen, many of these details don’t fossilize.

Another reason why it isn’t easy to say what killed off the saber-cats is that scientists can’t be sure, even for modern animals, which has a bigger influence on evolution – the physical environment or interactions with other living beings. (See details in Barnosky; Ezard and others)

How do you track everything in a world where, theoretically, one flap of a butterfly’s wings in the Amazon Basin can cause a typhoon in the West Pacific?

No one knows what tipped the scales against Homotherium, Megantereon, and Smilodon.
One clue to the 10,000-year-old missing sabertooth mystery may surprise you. It’s the fact that today everybody has to go to Africa in order to see big game.

We take this for granted, but it’s highly unusual for life on Earth. For at least the last 50 million years before that, big mammals thrived on every continent but Antarctica. (Prothero, 2006)

This was true right up until the last days of the sabertoothed cats.

wp-1485383621804.jpeg
You probably know about the Ice-Age mammoths and mastodons.
In North America there were other colossal animals, including beavers as large as a modern bear as well as buffalo with a 6-foot (2-meter) horn spread. (Prothero, 2006)

And there was Arctodus, a 1,500-pound (680-kilogram) bear – the largest carnivoran that has ever lived. (Prothero, 2006)

In Europe, sabertooths could hunt hippos, rhinos, and the “Irish elk” – a moose-like creature that was neither Irish nor elk – as well as other enormous prey. (Antón; Prothero, 2006)

The cast was different at that moment of geologic time, but it was the same 50-million-year-old story.

Then, several thousand years ago, after the last continental glaciers melted away and the world warmed back up into its present interglacial climate – the same sort of routine climate change that had already happened at the end of the previous nineteen ice ages (Smithsonian) – all those megabeasts vanished.(Prothero, 2006)

Yet at least half of all the other mammal groups from those days – mostly small- to medium-sized animals – are still around. (Prothero, 2006)

Indeed, naturalist Charles Lyell coined the word “Pleistocene” – from two Greek words meaning “most recent” – to describe fossils of marine shellfish that are still, for the most part, around today. (Smithsonian)

But all the land giants are gone now, and so are the sabertoothed cats.

The ice ages themselves had nothing to do with it, even though animals do tend to be bigger in cold climates since it helps them keep warm. (Heske, Lecture 17 and 18)

One look at Africa shows that animals get big in tropical climates, too.

Sabertooths and their prey easily handled the ice ages by migrating toward the Equator every 120,000 years or so as the great glaciers advanced. Then they followed their usual habitat back poleward as the ice melted and an interglacial period began. (Prothero, 2004)

They had done this nineteen times already. What was different about the twentieth go-round?

We might think that Smilodon and Homotherium were bound to be affected because they lived on megaprey.

And it does appear as though life was a struggle for big carnivores at the end of the Pleistocene.

The tooth fracture studies at La Brea show that all carnivores there broke their teeth more often than modern carnivores do, probably while picking bones clean. (Van Valkenburgh and Hertel)

But there is no evidence that the extinction of the big Ice-Age meat-eaters followed that of their prey. (Stuart)

And for some reason size wasn’t the only extinction factor.

Jaguar-sized Megantereon, which probably hunted animals, like deer (Antón), that are still around, also died off.

The end-Pleistocene megafauna extinctions are still a big mystery for paleontologists. (Stuart)

As for the sabertooths, they disappeared at different times on different continents. For example (Werdelin and others):

  • Africa: This was no refuge for saber-cats. Homotherium and Megantereon disappeared there about 1.4 Ma.
  • Europe: Homotherium vanished 500,000 years ago; Megantereon, around 1 Ma.
  • North America: Megantereon was gone 900,000 years ago. (Prothero, 2006) Homotherium went extinct some 10,000 years ago (Antón), and the last Smilodon sank into the tar at Rancho la Brea around 13,000 years ago.

Some experts on ancient life have found detailed evidence that these extinctions coincided with the arrival of humans on each continent. (Antón)

Others, while noting that manmade extinction has indeed happened on islands, say that the intercontinental Pleistocene extinctions can’t be explained so easily. (Prothero, 2006)

The sabertooths and their prey were probably affected by a complex series of events related to both the arrival of modern humans and global climate change. (See Stuart, as well as discussion in Prothero, 2006, Chapter 8, “Death of the Megamammals”)

Whatever happened, gigantic plant-eaters did die out everywhere but Africa at around the same time that the world’s ambush-and-slash niche emptied out.

It is tempting to think that this was cause and effect. But then why did saber-cats first go extinct in Africa, the Pleistocene big-game refuge continent?

Here’s another surprising clue.

wp-1485383968857.jpeg
The oldest known fossils of modern lions showed up in Africa less than two million years ago. Then, around 500,000 years ago, lions spread into Europe and parts of Asia. (Werdelin and others)

By 300,000 years ago, they were common in northern and eastern Asia. At this point, lions also crossed the Bering land bridge into North America and perhaps northern South America. (Werdelin and others)

Some experts wonder whether this had anything to do with the sabertooth extinctions. (Werdelin and others)

It isn’t clear what advantages lions might have had over sabertooths (Van Valkenburgh, 1999; Werdelin and others, but both types of cat do take big prey.

wp-1485383604534.jpeg

It probably takes several lions to bring down prey that a single sabertooth could handle.

And lions once had the most extensive range of any modern cat in the wild. (Martin, 1980)

Today they can live in forests, woodlands, scrublands, grasslands, and deserts, and they have even hunted seals on the coasts. Lions eat almost any land animal they want and snack on the occasional ostrich egg or other oddity. (AZA)

Their social behavior also changes in response to local conditions (AZA), although we can’t know how this compares to the behavior of sabertoothed cats.

In tough times, perhaps all of this adaptability gave lions a competitive edge over the saber-cats.

Anyway, the arrival of lions seems to match the times that Homotherium and Megantereon disappeared in Africa and Homotherium vanished in Europe.

But in North America, both sabertooth tribes lingered on for tens of thousands of years after lions got there.

And the American lion was a victim of the end-Pleistocene extinctions. (O’Brien and Johnson)

It’s a puzzle. Hopefully, further research, with better dating (Stuart), can show what actually happened to big animals at the end of the last ice age.

Jaguars, tigers, leopards, snow leopards, ocelots, caracals, lynxes, and an assortment of Felis cats all survived the Pleistocene extinctions. (Turner and Antón; Werdelin and others)

Wildcats – the housecat’s ancestors – actually diversified! (Yamaguchi and others)

Wait – where did all these modern cats suddenly come from?

They were there in the background all the time, starting with a pseudaelurine cat, but not the one that gave rise to the Knife-Tooths.

“Normal” cats then diversified and became widespread down through millions of centuries while sabertoothed cats arose and took over the world.

wp-1485383772134.jpeg
By 6 Ma, “normal” cats even came in sports models!

These cats fit into a different ecological niche and so were well suited to take small prey that an ambush-and-slash predator would ignore. (Werdelin, 1989)

Perhaps all of them, not just Leo, had an impact on their sabertooth cousins. (Werdelin and others)

It now seems like cats are multiplying like tribbles, but we will try herding them next time by talking about the new way that scientists are studying sabertoothed cats.

Then, we’ll move on to see how modern cats evolved and spread over the world.


IMAGES:
Featured image: Barbourofelis fricki, Museo di Paleontologia di Firenze: Ghedoghedo. CC-SA 3.0. Edited by RH.

Smilodon populator, Hungarian Natural History Museum: Tiberio. Public domain.

Barbourofelis loveorum, Florida Museum of National History Fossil Hall at University of Florida: Dallas Krentzel. CC-BY 2.0.

Yawning jaguar: Charles J. Sharp, Sharp Photography. CC BY-SA 4.0.

Homotherium crenatidens, Muséum national d’Histoire naturelle, Paris: Ghedo. Public domain.

Smilodon upper skull: Cope, E. D. 1880. On the extinct cats of America. American Naturalist. xiv (12):833-857, figure 13.

Man and sabertooths: Manedwolf. CC-AttSA 4.0 international.

Dinictis and Protoceras. Charles R. Knight. Public domain.

Female leopard in the Sabi Sands of South Africa: Profberger at English Wikipedia. CC BY 2.5.

Margay cat. Malene Thyssen. CC BY-SA 3.0.

Machairodus aphanistus, Museo Arqueológico Regional de la Comunidad de Madrid (Alcalá de Heneres).

Combined image:

  • Top: Proailurus, Cope, E. D. 1880. On the extinct cats of America. American Naturalist. xiv (12):833-857, figure 1.
  • Bottom: Machairodus. Ghedoghedo. SEE PAGE CC att SA 3.0 unported, 2.5 Generic, 2.5 Generic, and 1.0 Generic.

Leopard in tree: Siddarth Maheshwari. CC BY-SA 3.0.

Megantereon, Natural History Museum, Basel, Switzerland: Ghedoghedo. CC Att SA 4.0 International.

Xenosmilus, Gainesville-Florida Museum of Natural History. Jared. CC att 2.0 generic.

La Brea tar pit, circa 1910. Public domain.

Smilodon skull from La Brea: James St. John. CC BY 2.0.

Thylacosmilus atrox, American Museum of Natural History. Claire Houck. CC Att-SA 2.0 Generic.

Mammoth (Mammuthus meridionalis), Museo Paleontologico di Montevarchi. Emiliano Burzagli. CC BY-SA 3.0.
Two lions: https://pixabay.com/en/lions-male-female-lion-licking-paws-175933/

Lions hunting. Corinata. CC BY-SA 3.0.

Eurasian lynx: Bernard Landgraf. CC BY-SA 3.0.


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