Wednesday, July 25, 2007

Jaw biomechanics of Smilodon fatalis 2

I attended the 8th International Congress of Vertebrate Morphology (ICVM8) in Paris last week. There were a lot of interesting talks and I personally felt like I had information over-load!

One talk in particular that I found extremely interesting was that by Adam Hartstone-Rose, a PhD student at Duke University, who had painstakingly collected data of the physiological cross-sectional areas (PCSA) of extant felids, something I've always thought was in dire need. I'm particularly interested in this because this allows us to estimate bite forces in felids to a fair amount of accuracy. The most common source for bite force estimates in mammalian carnivores come from dry skulls which have been shown to underestimate (Thomason 1991). Bite forces estimated from calculations based on PCSA on the other hand seem to be in more congruence with actual in vivo bite forces (Thomason 1991). As there are currently no studies except for Binder and van Valkenburgh (2000) on in vivo bite forces in large carnivores, Adam's study on PCSA in large cats will most definitely be a valuable resource for functional morphologists.

Another cool talk was one by Blair van Valkenburg and Graham Slater (delivered by van Valkenburgh) on the cranial morphology of sabre-tooths. Results from a geometric morphometrics analysis was presented on the cranial morphology of extant cats and different sabre-tooths. Interestingly, sabre-toothed felids (macairodonts) are extreme morphotypes of modern cats diverging from extant feline morphology in which the rostrum becomes more upturned. If I remember correctly, similar trends can be seen in sabre-toothed nimravids as well. So this morphological trait of an upturned rostrum is pretty much associated with hypertrophied canines. It does make sense to have a more upturned snout if you've got massive canines.

Van Valkenburgh also briefly mentioned something interesting which made me think a bit. She suggested that perhaps sabre-tooths were extremely fast killers. At the time it didn't make much sense to me as I'd thought that sabre-tooths probably bit off chunks of flesh from the prey and waited for it to die of shock and loss of blood (Akersten 1985). However, I eventually grasped the potential that sabre-tooths may have bit into the throat much like some large cats do today but completely severed the trachea and any large arteries thus killing the prey almost instantaneously. When modern cats go for the throat or muzzle it tends to be a rather lengthy process as the canines sometimes don't even break the skin and they have to wait for the prey to suffocate (if I'm not mistaken - at least that's what it sounded like from the talk).

So the bottom line is: any kind of hunting strategy could have been possible for Smilodon as long as they kept their canines away from forceful contact with bones...

Reference:
Akersten, W. A. 1985. Canine function in Smilodon (Mammalia; Felidae; Machairodontinae). Contributions in Science 356:1-22.

Binder, W. J., and B. Van Valkenburgh. 2000. Development of bite strength and feeding behaviour in juvenile spotted hyenas (Crocuta crocuta). Journal of Zoology 252:273-283.

Thomason, J. J. 1991. Cranial Strength in Relation to Estimated Biting Forces in Some Mammals. Canadian Journal of Zoology-Revue Canadienne De Zoologie 69(9):2326-2333.

Wednesday, July 11, 2007

Felid skulls

I've been looking at and taking measurements from felid skulls now for a few weeks. I've been up in Edinburgh at the National Museum of Scotland for three days and I've also been at the osteological collections at the Bristol City Museum and Art Galleries for the last week now. I've covered 30 species of the 41 recognised extant felid species.

The funny thing is that some of the older specimens in the Bristol Museum are either mislabeled or not labeled at all and we sat there for some time comparing specimens trying to ID the damned things. I'm starting to pick up some subtle morphological distinctions but it's all kind of useless unless I can link them to the right species. All I need is a list of diagnostic characters...