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Re: Theropod "migrations"



At 03:44 PM 4/23/99 -0400, Larry Febo wrote:

>> 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).

Actually, I was talking about Quaternary faunas...

>I can see where Canids
>and Felids could have crossed at the Bering land bridge.

Most of what I was talking about was not trans-Beringian distribution, but
about habitat (and therefore area) ranges within the New World and within
Eurasia-Africa.

>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.

Ah, I think I see where we are talking past each other.  In fact, we are
talking about two different things: habitats/ranges and migrations.

I (and Currie, in this context) are talking about environmental tolerances
(aka habitat) of individual species: in general, large bodied carnivores
tend to have areally broader species ranges because they have a greater
potential habitat (i.e., their food (meat) is available in a wide range of
environments).  Herbivores, on the other hoof, tend to have a more
restricted potential habitat because their food (particular species of
plant) has its own particular set of environmental tolerances.

The above statements are made without regards to migration.

Okay, now to add migration in: animal migration over land barriers are
likely if and only if the species' habitat includes the environment of the
bridge itself.  If their habitat does include the bridge, it's fine and the
species can cross; if the bridge is outside of the habitat, than the species
is very unlikely to cross.  (Note I am talking about land-land crossings,
not sweepstakes dispersal over water and so forth).

So, yes, particular species of herbivore came over the Bering with various
carnivores (and one really badass omnivore, namely ourselves).  However,
only those species whose habitat included the conditions of Beringia were
likely to cross: it is unlikely we'll ever find Great Pandas in North
America outside of the zoo, since they require bamboo as part of their
habitat, and bamboo isn't exactly part of the Beringian flora...

However, even once in the New World, the range of the *particular species*
of herbivore is most likely to be smaller than that of the particular
species of carnivore.

>> 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).

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.

[However, you have hit *exactly* the point of discussion I had been going
over lo those many years ago in Evo. Bio. seminar: if there really is a late
Late K faunal interchange between North and South America, it is very
different from many interchanges, because the hebivores (hadrosaurids and
titanosaurids) seem to move between the landmasses, whereas the big
theropods (tyrannosaurids and abelisaurids) don't.  Interesting distribution.]

Oh, and please note: some of the key work on dinosaur migration
(particularly that of Jim Kirkland and colleagues in the American Southwest)
was done years after Lessem wrote his book.

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