Re: Evolution of tyrannosauroid bite power

["Andrew A. Farke" <andyfarke@hotmail.com>]

Previously posted (can't find who posted this abstract originally):
> > Abstract: "Although proportionately the forelimb is very small, the 
> > mechanical advantage reveals an efficiently designed force-based 
> > system (vs. a velocity-based system) used for securing its prey 
> > during predation. In addition, the M. biceps is shown to be 3.5 times 
> > more powerful than the same muscle in the human, the straight, 
> > columnar humerus provides maximum strength to mass ratio to counter 
> > the exertion of the M. biceps, and the thick cortical bone indicates 
> > bone selected for ultimate strength. Such mechanical adaptations can 
> > only indicate that the arms were not useless appendages, but were 
> > usted to hold struggling prey while the teeth dispatched the animal. 
> > _Tyrannosaurus rex_ was therefore an active predator and not a mere 
> > scavenger, as has been suggested."

I am going to second Mike's caution here. I'll first say that I love 
dinosaur biomechanics. I do dinosaur biomechanics on occasion. But. . 
.we need to be very careful when making statements about what bone 
morphology does or doesn't say about function and soft tissue. Mike's 
point about ostrich humeri highlights this perfectly. Furthermore, a 
recent paper (in the primate literature) by some of my colleagues from 
Stony Brook illustrates this in more detail:

Boyer, D. M., Patel, B. A., Larson, S. G., & Stern Jr., J. T. (2007). 
Telemetered electromyography of peroneus longus in Varecia variegata and 
Eulemur rubriventer: implications for the functional significance of a 
large peroneal process. Journal of Human Evolution, 53(2), 119-134.

I know it's not a dinosaur, but hey. . . So primate paleontologists (and 
neontologists) have long suggested that a large peroneal process on the 
base of the first metatarsal is correlated with grasping behavior (the 
opposable big toe). It makes basic biomechanical sense, because you'd 
want to pull on the base of the big toe in order to oppose it, and all 
the mechanics seem to work out. The peroneus longus attaches to this 
process, so it is then suggested that fossil animals that have a big 
peroneal process had a big peroneus longus, and were thus good graspers. 
The reverse applies, too. So Doug and Biren and Susan and Jack put some 
electrodes into the peroneus longus on some lemurs in order to measure 
muscle activity during grasping, and. . .nothing. Very little activity 
in peroneus longus during grasping. Another presumably good assumption 
bites the dust.

Other studies have found mixed links between process size and muscle 
size. . .my main point is that a lot more work needs to be done on 
understanding form/function in modern animals before we jump into 
statements about dinosaurs. Mike's work on cross-sectional geometry in 
birds is a great example. So is John Hutchinson's work on dinosaur and 
bird locomotion. If nothing else, my own dissertation work has made me 
rather. . .cautious. . .in trying to say anything about skull function 
without really understanding the modern systems. I'm hoping that perhaps 
this discussion might spur members of the list to use dinosaurs as a 
tool to identify the really big gaps in our knowledge of functional 
morphology!

Happy New Year (and back to the dissertation),

Andy

[p.s.-any other list members going to be at SICB?]