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Wait! Come back! (And try not to scream so loud.)

Does that accurately drawn, surprisingly well-preserved Pleistocene skeleton — now in the American Museum of Natural History, I think — look like a cat to you?

To help you decide, here’s a mountain lion skeleton for comparison. Other than size and some minor bony differences, all of today’s cats look like this under the skin (Turner and Antón):

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Note that:

• It’s not a camera-angle difference. The mystery critter’s back really is short and somewhat humpy compared to the long, flexible spine that helps modern cats to climb, sprint, and leap. (Antón)
• That tucked-in rear end on the mystery critter is very un-cat-like (while not shown here, other fossils prove that this animal had a very short tail, too). And its hind legs are actually a little shorter than the forelegs!



• All of the legs have thick, heavy bones; these must have supported incredibly powerful muscles during life. The same is true of the creature’s backbone near its shoulder blade, where the shoulder and chest muscles would have attached (hence the skeleton’s humpy shape).

  The mountain lion’s shoulders and chest are strong enough, but its streamlined build and long, slender leg bones are better for running, jumping, and other cat moves.

• Big Bones’s front end is sort of like the mountain lion’s, but it is put together differently. You can imagine this beast using those massive forelegs to grip something, like a large prey animal, and then wrestling it down to the ground and holding it there in a lock.

  The modern cat, on the other hand, is poised for either racing off or leaping away from (or possibly onto) the photographer.

Except for its unusually long, flexible neck, Big Bones is quite bear-like. But check out its saberteeth and retracted claws!

Well, cutting to the chase (pun intended), enough fragmentary DNA has survived to prove that Big Bones up there was a cat. (Barnett et al.)

Meet Smilodon, the most famous Ice Age sabercat! (And we haven’t even gotten to its long choppers yet.)

Misconception: A big cat with long teeth

Most of us imagine Ice Age sabercats as big cats with saberteeth.

So did BBC artists in their 2007 video reconstruction of a primeval kill (not embedded because they did CGI on a video of lions hunting, and parts of it are gruesome).

However, Big Bones up above is more like a bear than a lion. And you don’t see bears pursuing swift herbivores across the plain. Ambushing would be more Smilodon’s style.

Let’s start with the sabers, though.

These weren’t a new tooth type. Sabercats were mammals, just like the rest of us, and they inherited the same upper and lower canine/molar/incisor deal that all mammals got.

• Like all cats, sabertooths had a set of upper and lower back teeth that were meat-processing shears, called carnassials. This is true of all members of the order Carnivora, and it’s also why your cat or dog slices into food using the side of its mouth. Smilodon probably ate the same way, saving its sabers for the hunt.
• Let’s hold off on the incisors and lower-jaw canine teeth for now, other than to mention that the word “sabertooth” was first used in the 19th century for the cat’s grotesquely enlarged incisors (this usage changed to its present meaning four years later, when the first complete Smilodon upper canine came to light). (McDonald)
• As sabercats evolved, their upper canines got longer and flatter, like knife blades. The size and shape varied by species. Smilodon’s, of course, were FABULOUS!
  

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How about the bear-like body?

Obviously, even more was going on with these sabercats than the dental changes.

More fossil discoveries over the last century and much research by some of the best minds on the planet have gradually revealed that the sabercat’s entire body was adapted to fill a predator niche that’s difficult to imagine today, since no living cat uses it now.

The Ice Age world

Want to go on a field trip?

I’ve found a couple of helpful videos. These aren’t authoritative, but it’s still fascinating to see how different the world was back then.

These videos aren’t the be-all and end-all of what Earth was like during the Ice Age. But they ring true to everything I’ve read or have been told.

For example, a botany professor taught us that the beech-birch-maple hardwood forest of today’s northeastern US waited out the cold in a single cove in the Great Smoky Mountains and then spread northward as things warmed up.

Also, I have read that Europe’s Iberian Peninsula, Carpathian mountains, and parts of northern Italy were important shelters for animals and plants. (One lynx group stayed on the Peninsula after the ice cap melted back.)

Picture the many ways, most of them not recorded in the fossil record, that these changes must have affected sabercats, too!

Here’s the geography:

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And now the animals and plants:

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This narrator subscribes to the “overkill” hypothesis for end-Pleistocene extinctions, but Prothero describes another view that blames it on climate changes. No consensus exists yet, although overkill does seem to have been the case on islands, while a case for climate change as the cause is made for extinctions in Australia/Sahul, per Prothero. It’s a very complex topic, especially for the sabercats, since modern cats were around, too, raising questions of competition and replacement.

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Now, Smilodon was strictly an American cat, its remains being found in South America and that part of North America south of the glacial front, with just one specimen, I think, recognized in Central America.

Smilodon’s origins are mysterious, too.

Per Werdelin and Flink:

1. One school of thought, supported by Antón and others, suggests that Smilodon evolved somehow from the Eurasian sabercat Promegantereon — shown briefly in this video about a “normal” (conical-toothed) prehistoric cat — from waaay back in the Miocene. They think that its descendant Megantereon — shown on the cover of Antón’s book (disclosure: I’m not associated with this book in any way other than as a happy reader) — eventually migrated into the Americas via the Bering land bridge and evolved into Smilodon.
2. Another position, taken by Werdelin and Flink, is that we just don’t know what ancestors Smilodon had and can only follow it back a couple of million years, in the Americas, to the early Pliocene epoch.

For what it’s worth, Earth started its current ice-age cycling in the early Pliocene, too. There was SO much going on!

As you can probably see now, it isn’t easy to figure out exactly how or why bear-like Smilodon evolved, but the big-picture view of the world that brought it about is amazing.

Reconstructing sabercats

In 2008, the BBC gave us a Smilodon that is a little closer to reconstructions done by paleoartists like Mauricio Antón:

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Paleontologists and artists use their knowledge of living feline anatomy to “clothe” a sabercat skeleton with muscles and other tissues. Then, using motion studies of living cats and other animals, they look at how the cat might have used its body.

It turns out that Smilodon probably was a wrestler!

Turner and Antón explore this idea in detail. Here are some online sketches by Antón of how Smilodon might have hunted.

Using its powerful front musculature, and with the help of a strong but short back, Smilodon stands on its hind legs to wrestle down a Pleistocene zebra-like herbivore.

No need for a mountain lion’s lithe frame and long, speedy legs in this cat!

Smilodon then uses its strong forelegs and weight to wrestle its unfortunate victim to the ground and pin it. Then, using its extra-long neck, the cat brings those deadly sabers into position for a killing bite that enters soft neck tissue, avoiding bones that could break the saberteeth.

Brrr. Words can be gruesome, too!

Not all paleontologists agree with this “canine shear bite” hypothesis, as Turner and Antón call it — the expert from La Brea in the closing video here, for example, sort of goes along with it but thinks the cats used their powerful neck muscles to stab the prey with their sabers.

Still, these explanations meet what few facts are known today about Smilodon and other sabercats.

Let’s look at some more of those facts before ending with a visit to La Brea Tar Pits — the world’s best and most famous source of Smilodon fossils.

Name: “Smilodon” means “sabertooth,” but this term was first used to describe the incisors, not the long, flattened upper canines. (McDonald)

Sabercats and other sabertoothed predators do have unusual incisors that are very large and arch outwards instead of forming a straight line between the canine teeth.

You can see this arch very clearly in that drawing of Big Bones. The mountain lion’s incisors line up and can’t be seen from the side.

The canine shear bite idea explains this incisor arch as a way for the sabercat to hold on without risking the saberteeth breaking during the prey’s struggles.

Lineage: Smilodon and other sabercats all over the world belonged to a now-extinct subfamily of Felidae called Machairodontinae, the “Knife-Tooths.”

I think this group was a little older than the other recognized subfamily, Felinae (today’s conical-toothed cats and all their ancestors). At any rate, Felinae didn’t really get going until the end-Miocene extinctions in Eurasia took out all the older saber-toothed cats and cat-like barbourofelids, an event that also somehow gave us Homotherium and eventually Smilodon.

Data:

Taxonomists are still debating Smilodon, but here is one of the most common and easy-to-follow descriptions. Just be aware that “easy to follow” doesn’t necessarily mean “correct,” and as usual in science, all this will probably change a bit with time.

Some experts describe three species of Smilodon from Pleistocene times.

The oldest is Smilodon gracilis. It was a sturdy sabercat, 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 asphalt pits. (Antón)

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) in life. (Van Valkenburgh and Hertel)

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

As well, per Antón, the Fatalis skeletons provide an intriguing look into this cat’s lifestyle and some of the injuries it had:

• Despite their fragility, Smilodon didn’t break its saberteeth any more often than the 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 struggling 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 Smilodontini that have been found in North America thus far. (Antón)

But there is a third species known. It developed in South America, Smilodon populator, and was one of the biggest sabertoothed mammals ever. (Antón; Turner and Antón)

That 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)

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Here is a cool-looking 1:6 model (again, no endorsement implied; it just came up in a video search).

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Smilodon populator and the smaller S. fatalis divided up South America between them during the closing millennia of the Pleistocene, with Populator thriving east of the Andes, from Venezuela to Patagonia, while Fatalis terrorized the lands along the western coast. (Antón; Turner and Antón)

But eventually the last known Smilodon died several thousand years ago, caught in an asphalt trap that humans later named at La Brea.

Speaking of that famous museum, here is a class trip there, with a close-up look at S. fatalis from last December (remotely because of the pandemic ).

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Featured image: Cope (reference list), public domain.

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