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RE: Late Cretaceous Giant Ceratopsians and Hadrosaurs


Vlad Petnicki wrote:

We know that the really large dinosaurs - the sauropods
- had disappeared from Western North America by the
mid-Cretaceous, as the conditions changed and animals
got smaller.  They did not reappear until just at the
end, when Alamosaurus apparently migrated over a new
land bridge to South America, and made it as far as
Texas before the mass extinction.

This does appear to be the most parsimonious scenario. _Alamosaurus_ is phylogenetically closer to the saltasaurines of South America than to North American titanosauriforms such as _Cedarosaurus_ and _Venenosaurus_, which are of Barremian age. Thus, _Alamosaurus_ was probably not home-grown, but an immigrant from the south - based on current evidence. However, just to muddy the waters: the various bones referred to _Alamosaurus_ over the years appear to belong to at least two titanosaurian taxa. This would indicate that more than one titanosaurian existed in the Campano-Maastrichtian of the American Southwest, and these taxa may have had separate origins.



Tim

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