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Re: re: T. rex

>Not to be a wet blanket, but none of the respondants considered T. rex as
>a scavenger, which would conceivably help explain the mini arms.  Granted
>Albertosaurus/Gorogosaurus and a batch of other tyrannosaurids had
>similar appendages.

Actually, I don't see any advantage in "armlessness" to a scavanger that
doesn't apply to a canid- or hyaenid-style or phorusrachid-style predator.
Horner is sadly mistaken in saying active predators require their forelimbs
in predation.

>    I am impressed by studies suggesting T. rex (and by approximation, adult
>Albertosaurus, Daspletosaurus, Tarbosaurus, and the whole gamut of
>oversized relatives as adults) had insufficient femoral bone mass to
>sustain running speed (e.g. R. M. Alexander, "How dinosaurs ran" in
>Scientific American, --I'll dig up the date and page if anyone's interested).

Actually, Alexander's studied was seriously flawed.  He used an 8 tonne mass
for T. rex, based on an incorrect scaling (a hip height of 3.6 m).  The
actual specimen "modelled" (its an atrocious model, by the way) has a hip
height of less than 3.2 m.  Scaled correctly, the mass is some 4.6 tonnes,
and the strength of the value almost doubles.  However, Farlow et al. have a
paper in review which might change some of this...

>If this is correct, then its unlikely they were (at least) pursuit
>predators.  Given that ceratopsians _could_ gallop by the same analysis,
>as could hadrosaurs, T. rex must have been either an ambush predator
>or a scavenger.  THe latter seems more parsimonious to me, given the
>size (and smell?) of the beasts.

The evidence for running tyrannosaurids is much stronger than for running
ceratopsians.  The whole hind limb of a tyrannosaurid is desinged to be
elongated and gracile.  Ambush still might work, given the forested nature
of some the habitats they lived in, but pursuit still is possible.

Thomas R. HOLTZ
Vertebrate Paleontologist, Dept. of Geology
Email:Thomas_R_HOLTZ@umail.umd.edu (th81)