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Re: Theropod "migrations"



On the way in which herbivores may have broken the rule and hopped between N
& S. America better than large carnivores, perhaps this would be easier if
the landbridge existed in the form of "drifting" islands too small to
sustain a population of large carnivores.  The gigantic ape on an island in
the Indian Ocean known unofficially as "King Kong" provides an example.

The BCF considerations in migrations are very interesting, though
allosaurids and their ancestors would have been incapable of crossing any
wider stretches of water than sauropods could have swum in my view.  I don't
see even proper early birds managing 100 miles at a single hop.  In my view,
arctos (eg Troods, Tyrannos etc) stemmed from these early forms, so the
continent with the earliest Troods (Asia) probably tells us where flight
evolved (unless remains are ridiculously unfairly patchy), though a good
alternative would have been the European archipelago.

Jaime suggested "raptors" were originally american; I suspected that arctos
stayed in Asia at first, and only "uncinants" such as "raptors" got to
america in the earliest stages.  I still suspect that may be right, but I
now believe "raptors" were in asia from very early on - apart from anything
else, the feathered thing with ovi affinities (an "uncinant" for me) is v
early asian.

I'm not convinced about uncinants/arctos in Australia, nor in S. America
until landbridges could explain them.  However I do suspect there is
evidence for early birds showing better water-crossing ability than anything
else: if early birds really did reach the Tendaguru, then that was the only
group to have crossed between Asia and Africa at that time.  If the
Velociraptor/Deinonychus family were found in both Asia and America then
they were the only things that crossed there then.  Alternative explanations
need to go back to the early Jurassic


Doesn't that supposed Allosaurus eating a hominid looks more like a
dilophosaur ? :-)
( I wish people who start stories like that didn't sound so much like me!)

On that topic, I once suggested to John Maynard Smith that Evolution
couldn't be tested either, and he replied "What if you found a rabbit in the
Precambrian?"  It seems this sort of thing is a potential test (if valid of
course); the fact that it is not an experiment we can run and control
ourselves doesn't prevent it being a test.  The transit of mercury or
whatever it was, just after WWI, was of course the classic test of any
theory (relativity), and was something that just happened, in the same way
as the Pre-Cambrian rabbit would be.


JJ

http://www.geocities.com/CapeCanaveral/Hall/2099/DinoKabin.html