The Sabertooths, Part 3: Sabertooths Down Through Time

Saberteeth 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)

Members of all four, plus the very first sabertooths – Permian gorgonopsids – 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. There is more information about this ancient predator below.

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 mentioned yesterday:

  • Homotherium (purple). It first appeared in Eurasia about 6 Ma (million years ago) and in North America around 4 Ma. (Werdelin and others) It went extinct about 11,000 years ago.
  • 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

You probably have never heard of nimravids. They’re cool, though – the first “catty”-looking mammals ever!

Well, it’s more correct to say that sabercats and modern cats look like nimravids than to call nimravids cat-like, but very few people outside the paleontology department will know what you’re talking about.

Paleontologists may add that skeletal and cranial details prove that nimravids weren’t true cats, although these old sabertooths were mistaken for cats when their fossils were first discovered.

Nimravids were the first known hypercarnivorous mammals of the post-K/T world (Holliday and Steppan; Van Valkenburgh, 2007), and they had the same basic feline body plan as Fluffy – long legs, retractable claws, and sharp teeth. (Bryant; Turner and Antón)

No wonder early paleontologists called them “paleofelids.” It seemed obvious that these animals were the ancestors of modern cats, i.e., “neofelids.” (Antón)

But further research showed that they weren’t related to the cat family in any way. (Antón; Averianov and others; Werdelin and others)

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

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

Dinictis and Protoceras

The nimravid Dinictis chases Protoceras, possibly a distant relative of modern camels.

They went extinct around 23 Ma.

And that’s about all we definitely know about the history of nimravids.

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

Barbourofelids are more of an evolutionary challenge.

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

Barbourofelids were also very cat-like, so this time around, everybody thought they were just a second wave of nimravids. (Bryant)

Then more study showed that they weren’t nimravids. Perhaps they were cats . . . perhaps something unknown. (Werdelin and others) Anything to be mysterious!

But barbourofelids were at the top of the food chain while true cats and sabercats evolved, and barbourofelids were sabertooths. Did they influence the development of the first sabertoothed cats?

No one knows.

Pseudaelurus

In Europe, the Pseudaelurus complex of true cats emerged around 20 Ma (still the Miocene). North American pseudaelurines either evolved separately or else immigrated there from Asia later, 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)

wp-1485383676784.jpeg

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 pseudaelurine species had to be involved – one species for modern cats and another one for the sabertoothed cats. (Rothwell; Salesa and others, 2011; Turner and others; Werdelin and others)

Why two?

Because, 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)

Modern cats and the sabercats both belong in the cat family Felidae, 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 Machairodontinue, or “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 easy-to-pronounce 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)

If you got a quick glimpse of it in the forest, though, P-Quad would look like a modern cat, with a short face, long back, and long hind legs for getting around in trees. It might have had a spotted coat. (Turner and Antón)

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

Pseudaelurines lived so long ago that they didn’t have long hindfoot bones yet, like today’s cats. This evolutionary adaptation 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.

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)

To be continued tomorrow

Images:
Featured image: Gorgonopsian, by MaropengSA, Flickr. CC BY 2.0.

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.


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This series on sabertooths was originally posted at my Robin Huntingdon blog about a year ago.


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