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RE: Theropod "migrations"



On Monday, April 26, 1999 9:15 PM, veselinka.stanisavac   
[SMTP:veselinka.stanisavac@siol.net] wrote:
>  << File: Header.TXT >>
>
> 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).

One possible scenario that crossed my mind is based some rather localised   
catastrophe (this touches some of the KT-speculations, actually). Maybe a   
local epidemic, flood, draught, bushfire, vulcanic eruption, whatever...

Of course (relatively) many herbivores often need to browse some sort of   
vegetation, meaning they have to eat many many relatively small mouthfuls   
for very long periods of time, while (relatively) many carnivores catch   
or find something to eat, eat as much as they can and then go about   
essentially without food until they are both hungry again and the next   
fooditem "comes along" (either caught or found).

This means relatively speaking, carnivores can "hop" much more easily   
from one group of potential prey to the next, which can be quite some   
distance away, while herbivores need more of a "green trail" to follow   
while migrating.

I can imagine one of the mentioned local catastrophe killing parts of   
both (edible) vegetation and the animal in a certain small local area.   
After that the left-over herbivores in the area continue feeding on the   
left-over vegetation, maybe doing a relatively slow migration away from   
the affected area towards unaffected area's. The remaining carnivores   
however could first feast on the victims from the event (not always   
possible of course, depending on the catastrophe). Perhaps they could   
even catch/eat the remaining herbivores and then have a full belly both   
nothing more to eat. Especially if the local event is a draught and the   
vegetation suffers severely and thus also the herbivores.

What would such a small group of carnivorous animals do that is the area   
they alwasy lived in but that no longer contains enough food for them or   
even food at all? They search for food. Such a group could very easily   
venture quite a long way into territory previously unknown to them; they   
really have no choice. Even if the group wanders around and finds nothing   
after all, in the course of millions of years I'm sure something like   
this must have happened at least regularly I guess, so even if say a   
percentage of such groups actually finds "a new home" succesfully before   
starving you would have an example of the kind of "osmotic barrier"   
mentioned.

Just some speculation by a computer programmer interested in the   
Mesozoic. Go ahead, fire at will.. (Oh no, sorry. Leave Will out of this.   
Just fire answer at me please. <grin>)

Met vriendelijke groeten,
Jarno Peschier


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