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RE: biggest predators (Allosaurid "Dynasty")

> From: owner-dinosaur@usc.edu [mailto:owner-dinosaur@usc.edu]On Behalf Of
> Ken Kinman
>       And while we are on the subject, I'm wondering if the rise of
> Tyrannosaurs could have had anything to do with the extinctions
> of allosaurs
> and spinosaurs.  Or is it more likely their extinctions had other causes,
> and the tyrannosaurs just expanded to fill that empty niche?

I would LOVE to know the answer to that!  Unfortunately, data for extinction
by competition is extremely difficult to test in the fossil record.

In North America, at least, typical Late Cretaceous style tyrannosaurid
teeth do not show up until the the Albian-Cenomanian boundary, and thus
there is no positive evidence of the overlap of allosaurids and
tyrannosaurids in North America.  Tyrannosaurid-type teeth are present in
the Barremian of Japan, and teeth similar to tyrannosaurid (although not as
similar as the Japanese teeth) are known from the Morrison and Guimarota in
the Late Jurassic.  All of these are small,  however, from
_Deinonychus_-sized individuals or smaller.  So the only good evidence for
stratigraphic overlap between tyrannosauroids and allosaurids is for
individuals which would not likely be in competition as adults (assuming
that the tyrannosauroids were adults); this does not mean, however, that
there might not have been competition between young allosaurids and adult
early tyrannosauroids.

The only published evidence for stratigraphic/geographic overlap between
tyrannosauroids and spinosaurids is in Thailand, assuming that
_Siamotyrannus_ is a tyrannosauroid and _Siamosaurus_ is a spinosaurid...
Since tyrannosauroids are not presently recognized in Gondwana (unless
_Santanaraptor_ proves to be a tyrannosauroid), the tyrant dinosaurs and the
spinosaurids were in different geographic ranges, making competition moot.

                Thomas R. Holtz, Jr.
                Vertebrate Paleontologist
Department of Geology           Director, Earth, Life & Time Program
University of Maryland          College Park Scholars
                College Park, MD  20742
Phone:  301-405-4084    Email:  tholtz@geol.umd.edu
Fax (Geol):  301-314-9661       Fax (CPS-ELT): 301-405-0796