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Re: Rapetosaurus stuff



> (Particularly Utah and Texas, New Mexico to a somewhat lesser degree). This 
> may suggest a possible barrier between North and South NA during late K 
> times, across which titanosaurs could not move (just a suggestion, nothing 
> more). But if this barrier was real, than this would have limited 
> titanosaurs to northern NA during the late K, and they would not be present 
> in the southern basins. This seems to suggest to me that at least 
> _Alamosaurus_ had ties to SA.


Has anyone considered the possibility that climate had anything to do with
Alamosaurus remaining in southern NA?  I refer to an oldie but goodie:

Lehman, T.M. 1987. Late Maastrichtian Paleoenvironments and Dinosaur
Biogeography in the Western Interior of North America. Palaeogeography,
Palaeoclimatology, Palaeoecology, 60: 189-217.

In looking at various basins, the local geology, tectonic history, and
their faunal constituents, Lehman suggests that the changes that occur in
fauna from North to South (from a ceratopsian/hadrosaur to more
titanosaurid dominated fauna as one moves southward).  Too often I
think that we forget that dinosaurs were affected by climatic
conditions and these may have affected their distribution. There doesn't
seem to be overwhelming evidence for any type of large barrier that would
have prevented north-south exchange in NA.  Perhaps by the Late Late
Cretaceous, when the tectonic and climatic regimes were shifting, but the
distribution we see by then would have been affected by conditions that
prevailed millions of years before, as the migrations slowly took
place.  I think, then that it is quite possible for Alamosaurus to be of
Asian origin (or perhaps its ancestors, like Opisthoceolocaudia?), then
adapting to conditions that prevailed in southern NA, independently of SA
titanosaurs.  All that is lacking in this hypothesis is the fossil
evidence (probably wouldn't be the first time but...).  Hopefully I'm not
speculating too wildly.

cheers,
Chris

Dept. Geophysical Sciences
University of Chicago

"Watch out...I have a B.S.!"