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Re: Theropod "migrations"



----- Original Message -----
From: Thomas R. Holtz, Jr. <th81@umail.umd.edu>
To: <larryf@capital.net>
Cc: <dinosaur@usc.edu>
Sent: Friday, April 23, 1999 2:29 PM
Subject: Re: Theropod "migrations"


> At 12:48 PM 4/23/99 -0400, Larry Febo wrote:
> >It is noted how the late Cretaceous herbivorous species seem
> >quite different between Asia and North America, wheras the Carnivorous
> >variety were "more alike across continents" .Here Currie explains that
> >"Hunters are more mobile than their prey, quicker to exploit new
> >areas....and....tolerate a wider range of enviornments..."
> >I don`t know if I follow that reasoning. Why wouldn`t the herbivores make
> >the journey as well (after all, it`s proposed that they were likely to
have
> >undergone long distance seasonal migrations).
>
> This pattern is also discussed by Farlow in the Ostrom Festschrift, and I
> discussed it in Evol. Bio. seminar as a grad student... (not really
> documented, though).  The big difference between herbivores and
carnivores:
> many herbivores are relatively speaking specialists on certain plants.
> Different plant species, in turn, have fairly specific habitat
requirements.
>
> On the other claw, meat is meat.  If you can kill it, you can eat it (if
you
> are a carnivore).
>
> So, look at modern (or early historic) distributions of big cats (lions,
> tigers, leopards, pumas) or big dogs (wolves especially).  They often have
> transcontinental distributions: lions were found in Europe, Africa (from
> South Africa to the Mediterranean) and as far east as India in historic
> times.  Pumas range up and down the length of the New World.  _Canis
lupus_
> lived in the wild from sea to shining sea in North America and Eurasia.
>
> Now, how many individual herbivore species have (or had) this kind of
range?
> More particularly, how many *large* hebivorous species had these kind of
> ranges? Not too many.

OK. (Now I wish I knew more about Tertiary faunas) . I can see where Canids
and Felids could have crossed at the Bering land bridge. But didn`t also
many herbivores?? Like horses from N America to asia, and Camels (llamas) in
the other direction. The reason for their absence in many areas due to
prehistoric man`s intervention?? Which way did the Mastodons migrate?? I
don`t think they evolved  separately on both continents.

>
> >Well, BCF has an answer for
> >that,...the ancestors of these theropods just flew across these barriers,
> >and then became the secondarilly flightless predators that seem so
"similar"
> >in their anatomical details.
> >........why not??
>
> Why not??  Because I don't think anyone has ever suggested that
> _Acrocanthosaurus_ and _Giganotosaurus_ and _Carcharodontosaurus_ are each
> *separately secondarily flightless* descendants of an orignally flying
> carcharodontosaur (!?!?) ancestor!!  This is part of the pattern Sereno is
> discussing.
>

> 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???



> Thomas R. Holtz, Jr.
> Vertebrate Paleontologist     Webpage: http://www.geol.umd.edu
> Dept. of Geology              Email:tholtz@geol.umd.edu
> University of Maryland        Phone:301-405-4084
> College Park, MD  20742       Fax:  301-314-9661
>