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Re: Evolution of tyrannosauroid bite power

I'm wondering if the evolutionary increase in the jaw strength of tyrannosaurids is more a function of the adaptive response of the animal as a *system* to its environment, rather than just as some selective pressure acting on the jaws alone. For example, it seems to me that an adaptive shift in behavior, from snatching and manipulating small prey (as in *Guanlong vucaii*, in which the hands could do a large part of the work) to using the jaws to dispatch larger prey as quickly as possible (as in *T. rex*) would preferentially select for relatively smaller arms and relatively larger jaws. Animals are complex systems and need to be evaluated as such, more so than as a series of individual elements.


----- Original Message ----- From: "Thomas R. Holtz, Jr." <tholtz@umd.edu>
To: <stearns5@cox.net>; <dinosaur@usc.edu>
Sent: Wednesday, December 19, 2007 10:34 AM
Subject: RE: Evolution of tyrannosauroid bite power

From: owner-dinosaur@usc.edu [mailto:owner-dinosaur@usc.edu]
On Behalf Of Jamie Stearns
Sent: Wednesday, December 19, 2007 9:32 AM
To: dinosaur@usc.edu
Subject: Re: Evolution of tyrannosauroid bite power

I'm not sure about when the strong bite power evolved,but I
do seem to recall that Dilong and other early tyrannosaurs
were mainly identified as such from their cranial anatomy,
which would suggest that a distinctive skull was one of the
first things to evolve, and this may have some bearing on
when the jaw structure developed. However, I've yet to really
look at the structure of Dilong's jaws or anything for
evidence of its biting power.

The strong tyrannosaur bite did seem to evolve early on, although in stepwise fashion.

Snively et al. (2006) discuss this to some degree in:
Snively, E., D.M. Henderson & D.S. Phillips. 2006. Fused and vaulted nasals
of tyrannosauroid dinosaurs: implications for cranial strength and feeding
mechanics. Acta Palaeontologica Polonica 51:435-454.
(Available for free online at http://app.pan.pl/acta51/app51-435.pdf)

Thomas R. Holtz, Jr.
Email: tholtz@umd.edu Phone: 301-405-4084
Office: Centreville 1216
Senior Lecturer, Vertebrate Paleontology
Dept. of Geology, University of Maryland
Fax: 301-314-9661

Faculty Director, Earth, Life & Time Program, College Park Scholars
Fax: 301-405-0796

Mailing Address: Thomas R. Holtz, Jr.
Department of Geology
Building 237, Room 1117
University of Maryland
College Park, MD 20742 USA