Re: Hell Creek

[Danvarner@aol.com]

In a message dated 12/2/01 9:27:42 AM Pacific Standard Time, 
t_rexkwan@hotmail.com writes:


<< By the way, I have no idea what animals inhabited the Western Interior 
Seaway at this time. Was big ol' mean Tylosaurus still making life hell for 
Clidastes, Platecarpus & Elasmosaurus? Were Hesperornis & Ichthyornis still 
around? What about Archelon? >>

       Tylosaurines were still around in the form of 
Hainosaurus/Taniwhasaurus, but off-hand, I do not know of any records in the 
WIS at this time (but I've been out of the loop for several years now). 
Tylosaurus proper is gone (?). Plioplatecarpus has replaced Platecarpus by 
this time. The real difference is in the sudden radiation of the 
mosasaurines. Clidastes is gone, possibly having evolved into Mosasaurus 
conodon. Mosasaurus hoffmanni (maximus) should be there as well as several 
other species of Mosasaurus. Other mosasaurines present should include 
Prognathodon and Globidens and there is a tantilizing skull from high in the 
section that is begining to look very much like Plotosaurus. In the WIS, the 
higher you go the scrappier the record gets because it's getting shallow and 
more energy is present (there's a lot of damn crabs). The fish seem to keep 
steaming along, although Xiphactinus audax seems to be gone, being replaced 
in the gulf region by another species. I would venture to guess that 
hesperornithiform birds, plesiosaurs and Archelons were still around if the 
water was still deep enough.
       Latest Maastrichtian forms from California include Plotosaurus and 
Plesiotylosaurus (actually a mosasaurine, no relation to Tylosaurus), an 
elasmosaur, Hydrotherosaurus, and the turtle Osteopygis. DV