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Re: Tarbosaurus?



In a message dated 7/25/00 1:24:07 PM EST, znc14@TTACS.TTU.EDU writes:

<< Do you realize how complex an issue this is? In many, if not most, 
vertebrate populations, juvenile mortality is much higher than adult 
mortality. Thus, the ratio of juveniles to adults in the population may have 
very little to do with the ratio of juvenile corpses to adult corpses. >>

If you would stop being a gratuitous flamer, take the feet out of your mouth, 
and go to the trouble to actually READ my posts, you'll notice that I am NOT 
talking about juveniles, and I've been pretty careful to edit my posts so 
that the discussion will focus on SUBADULTS and their relationship to ADULTS. 
Juveniles are a whole different ball game. I might have mentioned juveniles 
in earlier posts, but that was before the discussion sharpened the focus of 
the thread.

Yes, I do know how complex this issue is, but I won't just stand back and 
say, "Gee, look at how complex this issue is! What CAN we do?" I am looking 
for ways to SIMPLIFY the issue so that I can get a HANDLE on it. This is 
called REDUCTIONISM, and it's been a mighy helpful approach in science. Why 
bring in sedimentology and geology just now? If you're going to complicate 
matters to the point where you can't say anything meaningful about them, why 
bother discussing them at all? There will come a time when sedimentology and 
everything else become appropriate to the discussion, and that's when we 
should start talking about them.

At a fundamental level, the Nemegt and the Hell Creek are alike: they had 
rivers, riverbanks, and lakes; they had tyrannosaurids and other kinds of 
dinosaurs; they had forests and lowlands at various locations. If you handed 
a professional geologist experienced in both formations a rock from the 
Nemegt and a rock from the Hell Creek, I doubt he could tell you which was 
which without a great deal of analytical work. The idea that subadult 
tyrannosaurids were somehow washed away in the Hell Creek, or dissolved in 
acidic soil, etc., leaving just full adults as fossils, but for some reason 
were not washed away or dissolved in the Nemegt, has to be--at the very 
least--questionable. There is no geological or sedimentological process I 
know of that would do this thorough a sorting of a population of 
similar-sized individuals in either formation, consistently across several 
different facies (remember, we're talking about the whole Nemegt, and the 
whole Hell Creek/Lance/Scollard complex, not just a single bone bed at a 
single locality). The sorting had to be done in the living populations, 
pre-mortem, before fossilization. Either fully adult tarbosaurs left the 
Nemegt region to the subadults and went elsewhere, or the subadults aren't 
really subadults but are full adults of a species different from what are 
called "full adults": a situation something like that in Africa, where the 
smaller leopards live alongside the larger lions. The second alternative has 
the virtue of making the fossil distribution of the two putative Nemegt 
species match that of the Hell Creek tyrannosaurids; the weird difference 
between the two regions vanishes.

Whether or not this is the REAL explanation of the difference between the 
Nemegt and Hell Creek tyrannosaurid fossil records I certainly have no idea, 
and it would indeed require all kinds of work to eliminate and constrain 
alternatives. But it is suggestive. And as far as a "statistically 
meaningful" sampling goes, the fossil record of tyrannosaurids in Mongolia 
and North America is about as good as we get for any dinosaur group in those 
areas.

And that's all I have to say on this subject. Period.