Wednesday, April 2, 2008

Why Saber Teeth?

So why should a mammalian carnivore have saber teeth? Modern large carnivores seem to function perfectly well without them, although sabertoothed cats did go extinct fairly recently in the Late Pleistocene. Superficially, it would appear that saber teeth would be damage prone (and unrepairable) and cumbersome to use, but their presence in at least four* separate mammalian lineages indicates they can be advantageous in some situations. Even the non-mammalian Gorgonopsians have been called "sabre toothed reptiles" by at least one person (Jenkin 2001), despite the fact that they're not reptiles and elongated canines aren't exclusive to them in Synapsids. Enlarged canines are present in other groups such as the herbivorous Dinocephalians and Dinoceratans as well as molluscivorous walruses- but I'm not getting into that right now.

*And this is not considering the possible nimravid/barbourofelid split.


I carefully had to specify that no large Carnivorans have saber teeth because one genus of medium-sized felid has some surprisingly sabertooth-like traits. This really seems like a great opportunity to shed light on why saber teeth would evolve. The felids in question are from the genus Neofelis (There are two species now - Kitchener et al. 2006), also known as clouded leopards, and their long canines are often cited in popular articles. Christiansen noted that the morphology of the species was not well studied previously and was the first to properly describe the sabertooth-like characters - in 2006.

The upper canines are far out of the range for living felids, the canine length is proportionally close to sabertoothed cats such as Homotherium and nimravids (feliform sabertooths) such as Dinictis. The lower canines are small compared to the upper pair, although their overall length is still proportionally larger than any living cat and apparently most sabertooth cat genera except for the primitive Paramachairodus. Large canines necessitate a large gape, a it appears that Neofelis is capable of the widest gape (~90 degrees) of any living Carnivoran and within the range of sabertoothed carnivores. Relevant features related to such a gape include a ventrally deflected jaw joint, a posteriorly rotated facial portion of the skull and a low symphysial angle; all of these features are out of the normal felid range and within the sabertooth carnivore range. Other features such as zygomatic arch thickness, origin/insertion of the temporalis and carnassial-jaw joint distance, however, are within the range of modern felids.

So why would Neofelis evolve these characteristics? Genetic evidence indicates it is a sister taxa to the pantherine cats which don't have any of these traits, and the fossil record doesn't provide any evidence of when the traits evolved. Christiansen noted that the ecology of Neofelis is also poorly known, but cited observations of it killing prey exceeding it in size. Neofelis accomplishes this by a bite on the nape, whereas large cats kill large prey with a suffocating bite. Christiansen believes that this method for a faster kill may have been due to significant competition in the Plio-Pleistocene. There isn't any hard data yet, but it does seem to be a reasonable hypothesis. Members of Carnivora are well known for re-evolving ecomorphologies (Valkenburgh 2007) and I can't help but wonder if a sabertooth guild is a inevitable part of feline-like diversification and competition. This doesn't mean that Neofelis will evolve into sabertooths, and why it only inhabits one locality cannot be known at this time. Convergent evolution and Elvis taxa always bend my mind.

Christiansen further states that we really need a lot more data on this genus. He brings up the possibility that early sabertoothed cats and nimravids (and Neofelis?) may be functionally quite different from the derived species, and may not even be considered "sabertooths". While Neofelis isn't perfectly analogous to sabertoothed carnivores, the revelation of it sharing so many derived characters should give fascinating possibilities for the study of sabertooths. I haven't seen any articles building on this yet, but it is still pretty soon.

This article turned out a bit shorter than I'd like, and I do still have those other lineages of sabertoothed carnivores to talk about...


-Cameron




References:
Christiansen, Per. 2006. Sabertooth Characters in the Clouded Leopard (Neofelis nebulosa Griffiths 1821). Journal of Morphology, 267:1186–1198 (2006).

Jenkin, Ian. 2001. Fossils Explained 33: Palaeozoic Carnivorous Reptiles. Geology Today, No. 17 V. 1 pp. 36-39.

Kitchener, Andrew C. et al. 2006. Geographical Variation in the Clouded Leopard, Neofelis nebulosa, Reveals Two Species. Vol. 16 Is. 23 pp. 2377-2383

Morlo, Michel et al. 2004. A new species of Prosansanosmilus: implications for the systematic relationships of the family Barbourofelidae new rank (Carnivora, Mammalia). Zoological Journal of the Linnean Society, Vol.140 No.1 pp. 43-61.

Valkenburgh, Blaire van. 2007. Deja vu: the evolution of feeding morphologies in the Carnivora. Integrative and Comparative Biology, volume 47, number 1, pp. 147–163

10 comments:

Camera Trap Codger said...

My Lord, you have here a very interesting topic. Saberteeth and canines in general show considerable variation in their resemblance to sabers and dirks, and Simpson wrote an interesting paper on the variation in their curvature and maybe their flatness. I think he also considered the presence/absense of blades on the anterior and posterior edges, and then he speculated about the mechanics of stabbing with such teeth. We need comparative morphological and behavioral data to plumb the depths of these adaptations. Many felids can take down large vertebrate prey without saberteeth, and there probably were several ways of doing it depending on the predator and its prey. Give us more!

Raymond said...

"Superficially, it would appear that saber teeth would be damage prone (and unrepairable) and cumbersome to use"

IIRC, Thylacosmilids had open-rooted saber-teeth and perpetual forward replacing molars. Are there *Thylacosmilus* fossils with
signs of regrowth on their damaged sabers?

Cameron McCormick said...

I'll give it a shot! The ol' institution for higher learning is kicking into high gear, but not for much longer...

Cameron McCormick said...

Raymond, I looked around and I couldn't find any reference to regrowth, but it does certainly seem possible. I'll keep looking, since this is another group that definitely needs expanding on.

Will Baird said...

Hi Cameron,

Speaking of sabre-tooth types, I not too long ago did a post on the gorgonopsids, should you all be interested.

Sordes said...

Very nice saberteeth I photographed at Tübingen: http://bestiarium.kryptozoologie.net/artikel/bild-des-tages-dinogorgon-schadel/
What is very interesting in Gorgonopsids is the complete absence of shearing teeth in the posterior part of the jaws. Sabertooth cats had often monstrous carnasials to tear off meat, but animals like Dinogorgon had nothing like this.

Caitling said...

Rather stupid questions, but I'll ask anyway. What's the difference between saber teeth and tusks?

Cameron McCormick said...

Did we get into that argument before?

Saber teeth are always elongated upper canines used for predation by hypercarnivores.

Tusks is a word used loosely for other elongated teeth, including canines. Walruses have elongated upper canines and feed solely on animals, but they eat mollusks and I'm not sure if the tusks have any use while feeding. A mollusk eating dolphin also had tusks, so I'm guess there's some relation. Baboons have preposterously elongated canines, but for some reason they're almost never called "tusks". Even manatees have tusks for cripe's sake!

Then we have deer (muntjacs, water deer) and deer-like animals (chevrotains, musk deer) that have elongated upper canines and occasionally they have been called "saber toothed". Saber-like tusk, tusk, or elongated canine have been used too and I think the latter is the most appropriate.

I hope this answered your query and didn't merely prattle off a bunch of facts and conjecture.

garrett1234 said...

i think this is one of the big mysteries in evolution but one that could be easily solved if you just look at the basic needs of the predator. I agree that the sabretooth evolved because of extreme competion with other predators it shared its environment with, the animal with the longest teeth can kill quicker and carry its prey farther and hold it securely if it had to defend against other predators better than ones with smaller teeth. Another use is the teeth could help the preadator take its prey to the trees like moder jaguars. and once these teeth evolved they could have been specialized for certain prey species witch would explain the differences you see in the fossils of sabretoothed animals.

garrett1234 said...

I know im right so email me back pretty please!!!!!!!!!