Re: segnosaurs

[Nick Longrich <longrich@stardot.com>]

On Wed, 11 Dec 1996, Nick Longrich wrote:

>       b) if you look at the front of the jaws of Erlikosaurus
> (Dinosauria, p 411) you see -isn't this curious- a series of little
> holes as seen in Deinonychus and T. rex, right about where the beak
> was. On the dentary, however, they end before reaching the end of the
> jaw.

        After perusing through the Dinosauria a little more, I did find some 
of those little holes illustrated on other animals, noticeably the 
prosauropods and the hypsilophpodont Tenontosaurus, not on the beak part 
but on the cheek part, although one did show a series of these ending 
just behind the predentary. So maybe the vascularization could support 
either, or maybe segnosaurs had big lips, not beaks? At any rate, it's 
not cut and dry. 
        Another thing I noticed was how low down on the dentary these 
little hole thingies are on T. rex, compared to being pretty close to the 
gums on the uppers. In Allosaurus, they don't go so far down. My 
supposition was that these supported something or other (horn, perhaps 
more likely lip) which sheathed the T. rex tooth, as opposed to the bare 
t. rex teeth Greg draws. If you look at the dentary, what you'll see is 
that, consistent with this argument, the holes up at the very front 
(under the incisiform teeth) are right near the gumline and those under 
the big maxillary teeth more or less follow the the cutting edge formed 
by the teeth and are far down from the gumline. What I suggest is that the 
lip (or horn, if you prefer)  that those vessel opening supported started 
lower down so that the teeth could fit down inside and be sheathed.