When I read Brian Switek’s excellent longform piece “Once and future cats” — about the history of the sabertooth cats — one passage jumped out at me:
While the future course of evolution is unknowable, there is a possibility that we are only in a short lull between sabercats. Long killing fangs have evolved so many times in the past 20 million years that there’s every reason to believe that a newly derived sabercat might evolve again. In fact, Per Christiansen, a zoologist at the University of Aalborg in Denmark, argued in 2012 that the clouded leopard — a mid-sized cat that prowls the tropical forests of Indonesia — has relatively elongated teeth and shows a great deal of similarity to true sabercats. Given a few million years, might the saber-toothed descendants of today’s clouded leopards slash at the throats of mid-sized herbivores of the future?
There’s something called a “clouded leopard” that’s alive right now but very similar to sabercats? Intrigued, I did some homework. Then I kept reading.
Let’s start at the very beginning — what is a clouded leopard? The name “clouded leopard” actually refers to two “somethings,” separate species of the genus Neofelis. Both are midsized, southeast Asian cats as Switek says, both are listed as “vulnerable” — a step short of endangered — and both are covered with gorgeous cloud-shaped markings.
But it’s not the markings that really impress — it’s the teeth.
The formidable teeth of the clouded leopard, courtesy of Eric Kilby via flickr.
Modern “big cats” — lions, tigers, jaguars &c. — generally have upper canines that measure less than 20% of the length of their skulls. But not the clouded leopard. Neofelis nebulosa has an average ratio of 23%, with some individuals possessing upper canines that measure a full 25% of the length of their skull. This ratio is an “outlier” among modern cats — an indicator of very long teeth indeed. It doesn’t approach the famed sabertooth cat Smilodon, whose impressive canines were a full 50% of the length of their skull, but it’s impressive nonetheless.
(As Smilodon enters the conversation, it should be noted that felids are generally broken down into three major “subfamilies”: the true sabertooth cats like Smilodon, all classified as machairodontines, are all extinct; the clouded leopard is a pantherine like many big cats; while housecats and some big cats like mountain lions and cheetahs are felines. Now back to the narrative.)
The clouded leopard’s impressive teeth led the previously mentioned cat-skull specialist Per Christiansen to publish a paper back in 2006 titled “Sabertooth Characters in the Clouded Leopard (Neofelis nebulosa Griffiths 1821).” Christiansen found that long teeth weren’t the only morphological outlier among the clouded leopard’s skull dimensions. For one thing, the clouded leopard’s face slopes back more like Smilodon‘s than a lion’s, allowing for a wider bite. And that wider bite showed up even more clearly when Christiansen looked at just how far a clouded leopard can open its jaw: he found that the clouded leopard is capable of achieving a “maximum gape” of almost 90 degrees. This is not only “the largest gape of any extant carnivoran” but also “a value normally considered feasible in extinct sabertooths only.”
In sum, the clouded leopard is not just “divergent and peculiar,” Christiansen said. Instead, his “analysis demonstrates that several of its peculiar features are actually characters present in, and in some cases considered characteristic of, sabertooth predators exclusively, and thus simply assumed to be absent in extant animals.”
The natural question is why — why does the clouded leopard alone among modern cats possess the peculiar combination of extra-long teeth and extra-wide gape? It’s hard to know for sure, given how little we know about the ecology of clouded leopards. Here’s what Christiansen proposed (edited lightly):
[The clouded leopard] is known to feed on a variety of arboreal mammals, such as monkeys and lorises, but also kills much larger prey, such as bearded pigs, hog deer, and muntjak, which either rival or exceed the body mass of Neofelis, demonstrating its ability to subdue large prey. There is one potential difference between the killing mode of Neofelis and other large felids, however. Large felids, such as the puma and the pantherines, often kill small prey with a powerful nape bite, but usually subdue large prey with a suffocating throat bite. In contrast, available evidence suggests that Neofelis kills even large prey and each other with a powerful nape bite. It may be that its enlarged gape and hypertrophied canines are an adaptation for nape killing of large prey, but this is, at present, speculation.
This “powerful nape bite” has been proposed as the evolutionary driver of “enlarged gape and hypertrophied canines” in past creatures like sabertooth cats. When competition is fierce, a predator’s ability to kill quickly — for example, by using huge teeth to puncture or tear out a throat as opposed to slowly strangling prey with a vise-like bite — provides a clear advantage.
That said, the clouded leopard does not appear to live in a particularly competitive environment for predators. Why the long teeth, then?
Well, Christiansen has an answer to that too: “potentially the Neofelis lineage may have evolved a number of primitive sabertooth morphological adaptations soon after the split from the pantherine lineage, but never became specialized owing to a lack of competition from other carnivores in the dense forest habitats.” In other words, if I have this right, several million years ago the clouded leopard diverged from the other big cats. At this point, there was intense competition that drove the clouded leopard into rapid sabertooth-ification. Then, when the clouded leopard came to fill a sufficiently unique ecological niche, competition died down and evolutionary change slowed down. The clouded leopard simply stayed semi-sabertoothed and carried on to today.
Christiansen P (2006) Sabertooth characters in the clouded leopard (Neofelis nebulosa Griffiths, 1821). J Morphol 267: 1186–1198. doi: 10.1002/jmor.10468.
Christiansen P (2008) Evolution of Skull and Mandible Shape in Cats (Carnivora: Felidae). PLoS ONE 3(7): e2807. doi: 10.1371/journal.pone.0002807.
Christiansen, P., Kitchener, A.C. (2010) A neotype of the clouded leopard (Neofelis nebulosa Griffith 1821). Mammal. Biol. doi: 10.1016/j.mambio.2010.05.002.
King, Leigha M. (2012) Phylogeny of Panthera, Including P. atrox, Based on Cranialmandibular Characters. Electronic Theses and Dissertations. Paper 1444. http://dc.etsu.edu/etd/1444.