Re: DINOSAUR digest 1271

[DRosent288@aol.com]

Astrodon--also called Pleurocoelus--is most likely a brachiosaurid (it has 
been
suggested it might be a basal titanosaurid)--a sauropod with long front legs,
simple, not divided, neural spines on its neck vertibrae, and wwide teeth.  
Whip
tail was a diplodocid--with peg-like teeth, shorter front legs, forked neural 
spines,
and skidlike chevron bones on its tail vertibrae.  Diplodocids were all but 
extinct in
the northern hemisphere in the early Cretaceous--a related group of 
sauropods, the
Dicraeosaurids, were thriving in South America at the same time, however--but
Braciosaurids lived in north America until the middle of the Cretaceous.  
Titanosaurids, sauropods with simple neural spines, peg-like teeth, and 
ball-and-
socket joints in their tail vertibrae--survived until the very end of the 
Cretaceous.
They started out in the southern hemisphere, but became worldwide in 
distribution
during the late Creaceous, filling the vacuum left by the demise of other 
sauropods.