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Re: Tarbosaurus?

In a message dated 7/21/00 8:33:39 PM EST, jeffmartz@earthlink.net writes:

<< But Tarbosaurus individuals probably DIDN'T die at the same rate
 throughout thier lives, if juvenile mortality was numerically higher then
 adult mortality, as in most animals. >>

If you assume that the population of tyrannosaurids remained steady within a 
particular locality, and the distribution of tyrannosaurids by age within 
that population didn't change, then each adult would eventually have been 
replaced by one subadult at some time, each subadult by a juvenile, and so 
on. So we need to know the clutch size of a tyrannosaurid nest and the number 
of viable hatchlings therefrom, as well as tyrannosaurid breeding strategy, 
before we can provide a proper mortality function for the population. These 
things we know very little, if anything, about. Simple Just So Stories, as 
usual in this business. Maybe this, maybe that. These things could well even 
out, so it is not entirely off the wall to pretend things are equal: 
reasonable first approximation, if nothing else.

The important thing is that the age distribution of fossilized tarbosaurs in 
Mongolia seems to differ significantly from the age distribution of 
fossilized tyrannosaurs in North America, and the question is, Why? Maybe 
it's breeding strategy, maybe it's preservational bias, and maybe it's 
because we are conflating populations of two genera instead of dealing with 
just one.