[Date Prev][Date Next][Thread Prev][Thread Next][Date Index][Thread Index][Subject Index][Author Index]

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.

>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).

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