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RE: Another question about Tyrannosaurs
From: Christopher
Pearsoll [mailto:c_pearsoll@hotmail.com]
Sent: Tuesday, May 29, 2001
5:35 PM
>I have a question
concerning tyrannosaurs. Are there one or two main branches of Tyrannosaur
evolution, where one, in
>Asia, led to the
larger tyrannosaur genera like Tarbosaurus and Tyrannosaurus, and the other, in
North America, leading to
>the smaller
tyrannosaurs, like Albertosaurus? For some reason, (maybe I half recall
reading this somewhere) I have been
>thinking that this
was the way the tyrannosaurs developed. I have since noticed that the
phylogenies of the tyrannosaur
>family do not appear
to bear the same concensus. If I am correct, please tell me. If I am
not, please tell me.
>
In
actuality, most recent tyrannosaurid phylogenies are strongly converging, with
_Alectrosaurus_ and _Alioramus_ outside the big guys, _Albertosaurus_ and
_Gorgosaurus_ as sister taxa, and _Daspletosaurus_, _Tarbosaurus_, and
_Tyrannosaurus_ forming a clade (most likely with _Tarb._ and _Tyr._ as
sisters).
These
results have been found by Currie, by myself, strongly suggested by Brochu (who
does caution the possibility of _Daspletosaurus_ being closer to _Tyrannosaurus_
than is _Tarbosaurus_), and by a few others in press or in
prep.
Thus,
there is no compelling evidence at present for a primarily Asian branch vs. a
primarily North American branch among the big guys. However, it should be
cautioned that we know so little about mesic (wetter) environments in Asia for
most of the Late Cretaceous that there might very well have been many genera of
giant tyrannosaurines there which are not yet discovered. (_Tarbosaurus_,
for example, is found in Nemegt beds, which are the "wettest" environment known
of the typical late Late K of Mongolia).
Thomas R. Holtz,
Jr.
Vertebrate
Paleontologist
Department of Geology
Director, Earth, Life & Time
Program
University of Maryland
College Park
Scholars
College Park, MD
20742
http://www.geol.umd.edu/~tholtz/tholtz.htm
http://www.geol.umd.edu/~jmerck/eltsite
Phone:
301-405-4084 Email: tholtz@geol.umd.edu
Fax
(Geol): 301-314-9661 Fax (CPS-ELT):
301-405-0796