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Re: Theropod "migrations"



----- Original Message -----
From: Thomas R. Holtz, Jr. <th81@umail.umd.edu>
To: Larry Febo <larryf@capital.net>
Cc: <dinosaur@usc.edu>
Sent: Friday, April 23, 1999 4:16 PM
Subject: Re: Theropod "migrations"
>
>
> >> And, again, I agree with Sereno on this: many of the similarities among
> >> mid-Cretaceous faunas worldwide are more likely due to mutual survival
of
> >> populations whose ancestral range included all these continents.  (In
> >fact,
> >> if Rauhut is correct in allying some of the Tendaguru teeth to the
> >> carcharodontosaurs, then this group was present back at a time of much
> >> faunal cosmopolitanism).
> >>
> >
> >OK, but what about T_Rex and its Asian counterpart Tarbosaurus Baatar?
Does
> >the Tyrannosaurid line extend back far enough to have been present when
> >Gondwana was whole? What about oviraptor?? What about Velociraptor???
>
> Well, oviraptorosaurs and dromaeosaurs ARE found in Gondwana (South
America
> and Africa, respectively, so far, with possible oviraptorosaur material in
> Australia as well).


Oops,...meant Laurasia. But OK, lets look at Gondwana too. Again, if you
look at the map at:  http://vishnu.glg.nau.edu/rcb/Late_Cret.jpg , even at
80Ma, the continents are pretty well split apart (unless this drawing is
inaccurate). These late Cretaceous theropods (Oviraptor and Velociraptor)
have a pretty wide distribution across many unconnected continental masses.
And Tyrannosaursa are also found both in Asia and North America. This seems
possible only if you believe in many "land bridges " connecting these
continents, in which case the seeming lack of exchange of Herbivores  seems
a bit unusual. Or, perhaps these theropods had ancestors well back into the
Jurassic, in which case you`d think they would have evolved even further
apart by the late Cretaceous. Or you can acknowledge the role of BCF in
these species dispersal.

>
> Tyrannosaurs seem to have been restricted to Asia prior to the earliest
Late
> Cretaceous (unless _Stokesosaurus_ is a tyrannosaurid).  Tyrannosaur teeth
> (as well as teeth of other groups known in Early Cretaceous Asia but not
in
> Early K North America) first show up in North America in the earliest
> Cenomanian deposits of the Cedar Mountain Formation.

So, how did it cross over to N America? Land bridge??