Re: Guts-Eating Spinosaurs

["Jaime A. Headden" <qilongia@yahoo.com>]

David Marjanovic (david.marjanovic@gmx.at) wrote:

<<And it seems to me the conical teeth were weaker to lateral stresses
[...]>>

<I'd say conical teeth are better for lateral stresses than laterally
flattened teeth, aren't they?>

  Yes ... typically, a cone resists bending better than the short axis of
a board, and the principle holds for teeth of comparable shape. However,
should the cone curve along it's long axis, this will alter the stress
along the curve rather than from the tip down, or towards the center of
the base, as is typical. A cone is a very structurally stable form except
when curved or bent. Hence the rostral teeth of baryonychines are actually
bad for the "stab"-attack style of predation suggested for spinosaurines
and seen in most longirostrine crocs. The teeth are designed to pierce and
hold by gripping with the jaws., However, crocs lack leverage, and have
somewhat curved teeth inward to resist the _outward_ stress of struggling
prey. Leverage in spinosaurids is given in height, a longer head, and the
ability to control the head and neck apart from the shoulders in a wider
cone of movement than would otherwise be possible. So the rules are
different. However, the teeth are different.

  Non-serrated, strait, and nearly perfectly conical, the teeth should
only be effective in one of two ways: 1) stabbing and holding between sets
of stabbing teeth, above and below, and 2) with the nature of the keel,
cutting. But the latter is not well supported, as a cutting tool for teeth
is best served by the presence of serrations and a concavedly curved
caudal margin, focusing stress through the thicker diameter of the tooth.
This is why cutting tools are better as flattened blades than keeled rods.

  Thus, the spinosaurine jaw was probably a long line of stabbing augurs
or the like, using jaw power to propel into the flesh. Thus, one should
expect enlarged adductor musculature, as in a deep postdentary and
enlarged interparietal crest. Such is seen in spinosaurids generally,
emphasising the closing apparatus of the jaw.

  Conversely, though they bear the famous "banana"-shaped teeth,
tyrannosaurines have a jaw that seems built more for torsion than
spinosaur jaws, and are laterally robust and designed to resist pulling
the teeth sideways out of the sockets (see Hurum and Currie's paper in the
2001 JVP (3 ... I think) -- I have the pdf if anyone's interested). The
jaws of tyrannosaurines are effective "twister" jaws (Holtz, 2000; see his
entries on the Arizona Tree of Life pages) as much as hyenas and some dogs
are. Thgis type of jaw and robust tooth, though not banana-shaped in the
least, is also seen in *Dromaeosaurus* as compared to velociraptorines,
and indication that the jaw was used primarily for subduing and/or
rendering prey moreso than the velociraptorines; hope that answers that
question. Both Paul (1988a, 1988b) and I have talked about this (I was
only onlist, but I support a head-first action in *Dromaeosaurus* while
*Velociraptor* and closest kin were probably hands/feet-first; the jaws
are narrower, more slender, and the teeth narrower and relatively
specialized. Comments in full when I get my blasted website up and
running.

  Pardon my language.


__________________________________________________
Do You Yahoo!?
Send FREE video emails in Yahoo! Mail!
http://promo.yahoo.com/videomail/