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RE: tiny-armed theropods
I believe the prevailing theory (and Tom Holtz can correct me on this) is
that limb reduction occurred as the head become enlarged (in tyrannosaurs),
such that the head is the primary tool for acquiring prey. This is emphasized
in enlarged neck and shoulder bones, more robust ribs, and a skull with more
intricate interlocking connections or bony stops (or fusion), which is designed
to reduce the stresses borne between bones when the skull is being used so
heavily. On top of this, it has been theorized that abelisaurids, specifically
*Carnotaurus*, used the head in disabling prey while at speed (Bakker and Paul
have somewhat romanticized this with "slash and run" attacks, although the
"strike and strip a chunk of flesh off" idea that was illustrated by Paul in
_Predatory Dinosaurs of the World_ emphasizes a more stationary strategy).
Tyrannosaurs, on the other hand, seemed suited to ambush attacks, literally
ramming their jaws into the flanks or whatever of the animal and doing a
considerable amount of damage while restraining the prey.
This is contrasted with smaller theropods or raptorial birds, in which the
limbs are the primary acquisitors, and the jaws are designed to deliver more
delicate attacks, or just to process flesh; in allosaurs at least, as in
abelisaurs, the teeth are very slender and much more suited to being drawn
through the flesh than in being rammed at high speed into the side of whatever.
So the short and skinny is that these animals were favoring use of the
cranium and jaws to handle and hold prey, rather than the limbs, and this may
have been predicated on the ambush, guerrilla strategy rather than a "hit and
run" type attack.
Jaime A. Headden
The Bite Stuff (site v2)
"Innocent, unbiased observation is a myth." --- P.B. Medawar (1969)
"Ever since man first left his cave and met a stranger with a
different language and a new way of looking at things, the human race
has had a dream: to kill him, so we don't have to learn his language or
his new way of looking at things." --- Zapp Brannigan (Beast With a Billion
> Date: Wed, 5 Oct 2011 03:47:22 -0400
> From: email@example.com
> To: DINOSAUR@usc.edu
> Subject: tiny-armed theropods
> Has anyone given any thought and proposed ideas why tyrannosaurs
> (north) and abelisaurids (south) developed their tiny arms on two
> seperate unconnected land masses - as in, what forces drove this to
> Is it just coincidence that they were both around at (generally) the
> same time-frame?