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*To*: jeffmartz@earthlink.net, dinosaur@usc.edu*Subject*: Re: Tarbosaurus?*From*: Dinogeorge@aol.com*Date*: Fri, 21 Jul 2000 20:47:40 EDT*Reply-to*: Dinogeorge@aol.com*Sender*: owner-dinosaur@usc.edu

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.

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