Re: Tarbosaurus?

[Dinogeorge@aol.com]

In a message dated 7/21/00 7:30:41 PM EST, jeffmartz@earthlink.net writes:

<< Hold on a second, I think that reasoning is skewed.  A Tarbosaurus
 spending 80% of its adult life as an adult implies that adult mortality is
 LOW, not high.  An individual doesn't die more frequently the longer it
 lives.   Most individuals that are born die as juveniles rather then as
 adults, so there should be more juvenile corpses dropping annually then
 adults (assuming that dinosaurs are like most "r strategy" modern animals in
 terms of juvenile mortality).  Even if the survivors live a long time as
 adults, most of thier siblings died young, so dead juveniles should still
 outnumber dead adults. >>

Right, this assumes that Tarbosaurus individuals died at about the same rate 
throughout their lives (that is, that the chance of an individual dying at 
any particular age is the same for all ages), a simplifying assumption made 
to avoid bringing even more unknown factors into the equation. But what we 
really are interested in here is a function that provides the chance of a 
Tarbosaurus fossilizing, given its age. All other things being equal, one 
might expect the distribution of ages of fossilized Tarbosaurus to be about 
the same as that of fossilized Tyrannosaurus rex, but it is not. It >does< 
become roughly the same (for both species, by the way) if there are >two< 
species of tarbosaurs, the smaller of which looks like a subadult of the 
larger.

If it's Tyrannosaurus rex that has the abnormal distribution, then we should 
be finding an occasional individual about 60 feet long--the adult of the 
subadults that we've been finding so many of lately.