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Re: Theropod "migrations"

-----Original Message-----
From: Thomas R. Holtz, Jr. <th81@umail.umd.edu>
To: veselinka.stanisavac@siol.net <veselinka.stanisavac@siol.net>
Cc: dinosaur@usc.edu <dinosaur@usc.edu>
Date: 26. april 1999 17:13
Subject: Re: Theropod "migrations"

>At 04:19 PM 4/26/99 +0200, Berislav Krzic wrote:
>>So the different rate of evolution change of
>>carnivorous dinosaurs and herbivorous ones in a new environment during a
>>certain (not very long) period led to the impression that mainly the
>>carnivorous dinosaurs were migrating. Fact is, they couldn't have migrated
>>very far without their food supply: they had to follow their prey - the
>>herbivores must have crossed the bridge first.
>While your hypothesis of evolutionary rates may be true, in fact the food
>supply for carnivorous dinosaurs was already there: the local herbivorous
>fauna.  So it is not necessary for them to follow the herbivores, since
>is already present.  (That is not to say that they *didn't* follow:
>our current resolution for the hypothesized earliest Late K immigration
>event isn't fine enough to tease out that level of detail).

I don't insist on the hypothesis. It is just one of the possible solutions.
However, I still have trouble in figuring out how meat eaters  moved on
leaving behind their (conservative - "immobile") herbivorous prey, just to
find eventual new prey "on the other side of the hill , across the desert,
across the river", etc. It could have happened just as an accidental event
(many times in a long history, of course) - a sole predator or a group -
crossing the "secret barrier" herbivorous dinosaurs didn't care crossing. A
sort of "osmotic" barrier: transparent for predators but not for herbivorous
dinosaurs (odd).

>That is the point of the comment "meat is meat": for most carnivores, it
>doesn't matter if it feeds on the meat from a local animal or the meat of
>animal from another part of the world.
>Many herbivores, however, have much more particular food requirements (only
>certain plant species), and thus cannot migrate (or immigrate) into new
>regions if their food stuff is not present.
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.
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.
they are present on both continents, too.

Berislav Krzic (Kr?ic)