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Re: Tyrannosaur Evolution
--- David Marjanovic <firstname.lastname@example.org> wrote:
> ----- Original Message -----
> From: "Tim Donovan" <email@example.com>
> Sent: Monday, February 14, 2005 5:41 PM
> >> Well, only if you limit the continent involved to
> >> "western North America" rather than "Asiamerica".
> > It has been suggested that there was only an
> > chain between Asia and NA but that may not be
> > if ankylosaurids radiated across.
> Research on the paleogeography of Alaska and
> Chukotka still being missing, I
> can only offer another speculation: perhaps climate
> acted as a filter.
Of course. Nodosaurs are another example. They may be
present in the Amur area but not in Mongolia.
> mammal faunas of Montana and Alberta differ, as do
> the vegetations... the
> land bridge was (if at all) much farther north
> still, with a long polar
> night and all. But perhaps the differences are not
> Asia/NA in the first
> place, but highland/lowland. Ceratopsomorphs rule in
> western NA, but are
> absent from Asia... except its western coastal plain
> (Özbekiston). The same
> holds for spalacother..oid mammals. Hadrosaurs are
> common in NA and rare in
?? Hadrosaurs are abundant in Nemegtian beds, and
seem common in Baynshirenian beds and even in some of
>but the Amur region seems to be stuffed
> with them. There are more
> examples like that, and they've been discussed
> > It would be odd for a basal tyrannosauroid to
> > coexist with a rather derived one.
> Only if their ecological niches were sufficiently
> similar to necessitate (!)
> competition. A casual glance at their body sizes
> suggests to me that this
> was not the case.
The idea of pygmy tyrannosaurs seems less credible
> > I note that all of the putative nontarbosaurid
> > tyrannosaurs from the region-Gorgosaurus
> > Maleevosaurus, even Alioramus-are known or
> > to be tarbosaurs.
> *Tarbosaurus* itself is one of the few things
> *Bagaraatan* is certainly not.
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