Re: T.rex as scavenger

[Tom Holtz <tholtz@geochange.er.usgs.gov>]

>If other large theropods did not have to rely on scavenging, then their
>argument (that rex was too big to be a hunter) falls apart. I don't think that
>small arms is much of a handicap, it may be a benefit. It allows larger jaws
>and/or (somebody else's idea) better balance. T.rex evolved from a smaller
>theropod, which was probably a hunter. It is more likely, IMHO, that rex's
>arms evolved smaller to make it a better hunter than that the arms evolved
>smaller just because they weren't needed anymore. Don't the other tyrannosaurs
>(eg. Albertosaurus) also have short arms? If so, you would have to say that
>all tyrannosaurs branched off of a medium-large theropod scavenger. Or (very
>unlikely) that all tyrannosaurs independantly evolved short arms

All tyrannosaurids have small arms.  Also, tyrannosaurids are the only
large theropods in the places/times they occur, so they couldn't be eating
kills made by some other giant predator.  This is especially true in the
late Maastrichtian, when Tyrannosaurus rex itself is the only large
predator in western North America, followed by Nanotyrannus (if it isn't
just a juvenile T. rex), and then the dromaeosaurids.

And, recent evidence suggests tyrannosaurids evolved from relatively small
(man-sized) predators with grasping forelimbs like troodontids and
dromaeosaurids.  There seems to have been a shift from the grasping to
pursuit-and-bite as, simultaneously, the skull became more massive and
better reinforced, the arms shrank, and the body size increased.

                                
Thomas R. Holtz, Jr.                                   
tholtz@geochange.er.usgs.gov
Vertebrate Paleontologist in Exile                  Phone:      703-648-5280
U.S. Geological Survey                                FAX:      703-648-5420
Branch of Paleontology & Stratigraphy
MS 970 National Center
Reston, VA  22092
U.S.A.