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Re: Tarbosaurus?

On Fri, 21 Jul 2000 Dinogeorge@aol.com wrote:

> In a message dated 7/20/00 6:55:45 PM EST, jeffmartz@earthlink.net writes:
> << If preservation of tyrannosaurs is so much more favored in the Nemegt 
> Formation then in North America, why can't you get unusually better 
> preservation of juvenile mortality as well? >>
> Considering that a large predatory dinosaur such as Tarbosaurus would 
> probably have spent 80% of its lifespan at its adult size, one would expect 
> 80% of the preserved specimens to be adults, not the other way round.

This view seems overly simplistic to me as it doesn't take into account
population dynamics and taphonomic biases. Consider for instance that
in many species (maybe even most) only a few individuals make it through
to to adulthood while most die before reaching sexual maturity (this is
after all how natural selection is supposed to occur). Personally I
think the Hell Creek tyrannosaurid sample is unusual in its rarity of
juvenile specimens, while the Judith River and Nemegt samples are closer
to what we should expect. Possibly some bias is working against the
preservation or recovery of juvenile tyrannosaurs in the Hell Creek.