Wednesday, July 30, 2008

Bite Club: Comparative Bite Force in Big Mammals

Log predicted canine bite force (CBS) plotted against log body mass (BoM). Regression for all extant taxa along solid black line. Individual data points are: for felids (open triangles), canids (grey filled triangles), dasyuromorphians (grey filled squares), thylacoleonids (black filled squares), hyaenids (grey filled diamonds), ursids, a mustelid and a viverrid (grey crosses), and a thylacosmilid (open squares).

Did you ever read a paper and then have a hard time finding it again? You know it's out there, but finding it again? That may take some drilling!

The good news is that I finally found a paper I was looking for. It's called "Bite club: comparative bite force in big biting mammals and the prediction of predatory behaviour in fossil taxa" (PDF)

Basically, the paper estimates bite force measurements based on the failure load of jaw bones of living mammals, i.e. when the jaw bone is used as a simple lever, at what point does it crack? This data is then regressed against weight to see trends, and then these trends are used to determine the predictive bite force values for extinct mammals.

Note that the graph uses a logarithmic scale, which is typically used when you are using comparative data sets with widely differing values (i.e the jaw strength of a 15-gram mouse versus the jaw strength of a 200-pound hyena.)

A couple of points made in the paper:

  • Body Mass Determines Most of It: The bigger the animal, the stronger the jaw and the larger its prey. Body mass alone is largely predictive of bite force potential.

  • Head shape matters: "The Mean Bite Force Quotient (BFQ) was lower in cats than canids, reflecting the smaller head size of cats relative to body mass, but relative to skull length, Canine Bite Strength (CBS) in felids was greater, possibly because of their greater skull width relative to length."

  • History Matters: Placental animals seem to have slightly weaker jaws than marsupials, and bone-crushing animals such as hyenas seem to have stronger jaws. That said, body mass largely determines bite strength.

1 comment:

Dr Dan H. said...

What may be going on with regards the difference between cats, dogs and marsupials is that the cats have the most specialised dental structures and need least force to achieve a kill (especially seen in the sabre-tooths), whereas the marsupials have much less well evolved teeth and also smaller brains so are biased towards force as opposed to finesse.

It would be interesting to model the bite forces of a few theropod dinosaurs on that scale as well, since they tended to plot right on the reptile brain-to-body size graph (i.e. really, really stupid compared to mammals) and had relatively undifferentiated teeth. Most theropods also had kinetic skulls, whereby flexible sutures in the skull and jaws could flex to avoid shock-loading the jawbones too much, which increases the total bite strength of the animal; reptiles also regrow teeth continuously so overstressing and breaking teeth is nowhere near the big deal that it would be to a mammal.

I strongly suspect that the smaller brained the animal is relative to body mass, the more it will be biased towards brute force and high bite strength as a killing method.