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Re: Theropod "migrations"



At 10:52 PM 4/26/99 -0700, Nick P wrote:

>>   Well, I'd think the water buffalo might qualify
>> here, to raise another non-dinoaur and my favorite
>> bovid to the fore. Their range (presently) includes
>> Africa, the Middle East, the Indian subcontinent and
>> South East Asia, Malaysia, and was introduced to
>> Australia.
>
>I always thought African and SE Asian water buffalo were different
>species.

Nick is correct.  The Cape Buffalo (_Synceras kaffer_) and the true water
buffalo (_Bubalus bubalis_) are two different species (genera, even).  It is
true, though, that these two both have pretty sizable ranges: _S. kaffer_ is
found throughout sub-Saharan Africa in watered, grassy regions; _B. bubalis_
is widel domesticated from Egypt to the Philippines, although it's original
native range is uncertain (the 1964 edition of Walker's Mammals of the World
states that it "...is said to be found in the wild in Nepal, Bengal, and
Assam, although some naturalists think that these are feral animals."  Like
_Synceras_, _Bubalus_ prefers dense grass and reed growth in moist areas.

So, the preferred food stuff of these taxa are found over quite large areas,
allowing them to have large areal ranges.  (Of course, _Bubalus_ gets a bit
of an assist from humans, as domesticated animals...).

Berislav Krzic wrote:
>I had the impression that the modern big carnivores have their favorite
>prey, too. Lions prefer zebras and wildebeests; cheetahs Thompson's gazelles
>and warthogs; etc. The kind they are specialized in catching. When the
>herbivorous preferable prey of these predators migrates, I believe the
>hunters follow them.

Again, no one is saying that predators don't have preferred prey species.
However, most carnivores can more easily make do with meat of animals
outside their preferred "menu" than herbivores can with plants outside their
preferred "menu".  Consequently, the areal range of large herbivore species
tend to be smaller than those of large carnivore species (not guarenteed,
not absolute, only tendencies).

>The dinosaur mega track  sites indicate that some herbivorous dinosaurs
>(ornithopods) were seasonal (?) migrants. Wouldn't it be possible, that
>when eventual geographic barriers vanished - say: a landbridge emerged from
>the sea - that the migrants just continued on their trail over the bridge
>into the new territory, a new continent? Coincidentally, we've got related
>ornithopods on both Asia and N. America in the L.K.
>Tyrannosaurids were the obvious predators on big ornithopods.
>Coincidentally,
>they are present on both continents, too.

Yes, no one is disagreeing here.

One final note from me: a couple of good papers on habitats, carnivore
ranges, and so forth, both found in the Ostrom Festschrift (American Journal
of Science volume 293-A):

Farlow, J.O.  1993.  On the rareness of big, fierce animals: speculations
about the body sizes, population densities, and geographic ranges of
predatory mammals and large carnivorous dinosaurs.  American Journal of
Science 293-A: 167-199.

Vrba, E.S.  1993.  Turnover-pulses, the Red Queen, and related topics.
American Journal of Science 293-A: 418-452.

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