Re: Regarding Spinosaurus -- ignore last message

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

Oops, ignore the last send, that was hitting the "go" before I had written
my reply

Waylon Rowley (whte_rbt_obj@yahoo.com) wrote:

<I was looking at Sereno's skull reconstruction of Suchomimus, and I
realized that every spinosaur dentary I've seen is lateromedially
compressed. If spinosaurs fed like some piscivorous birds (where they
"spear" or snatch fish from the water) then  wouldn't you expect frequent
damage to the bone if the animal missed its target?>

  In piscivorous, spearing fishers among birds, the jaws are not
mediolaterally compressed, but rather robust, seen in kingfishers
(Alcidae) and herons, storks, snakebirds, etc. (Ciconiidae, Gruidae,
etc.). These jaws are narrow, generally, but the mandibular rami are not.
There is generally no jaw action until after the fish is speared (the jaws
are never sealed, but kept partially open), which occurs by forcefully
ramming the beak through the prey in one quick stab.

  Spinosaur jaws are unique compared to even the other style of
fish-acquisizition known in the biological realm, that of crocodiles,
which use their jaws in a snatch-and-grab catch style. Their jaws,
however, are dorsoventrally compressed, and the mandibular rami are
flatter dorsoventrall or crescentic in section than they are
mediolaterally. Spinosaur jaws are expanded only at the rosette rostrally,
but also appear to be adapted to the "snatch-and-grab" style of catching
prey, in that a bar resists forces better along its long axis than at the
short axis. Stress reducding structures include the tighlty bound
supradentary and splenial elements, fused intradental plates, and dental
alveoli that are not greatly wider than the crown bases, but with roots
wider than the crowns (Buffetaut, 1992). This allows, along with teeth
arranged in direct parallel to the dorsoventral axis of the jaw in
section, very good bend-resisting stress reducers, and suggest the jaw
action was one of "open--close" in a very fast and very strong action.
Something interesting is that the jaw symphysis is not fused, unknown in
other fish-snatching predators, and the lack of a defined or rugose
symphysial plate in the jaw of *Spinosaurus* or the very small one seen in
*Baryonyx* (pers. obs.) indicate that the binding cartilage was either
small and weak, or absent, and that, as in *Torvosaurus* or some
carnosaurs, the jaws could move slightly independantly (*Torovosaurus*
also appears to have a very reduced symphysis, pers. obs.). Damn, why
don't I just right the paper now?...

  Other behaviors suggested for the feeding style of spinosaurs (waiting,
etc.) are not supportable by the present fossil record.

=====
Jaime A. Headden

  Little steps are often the hardest to take.  We are too used to making leaps 
in the face of adversity, that a simple skip is so hard to do.  We should all 
learn to walk soft, walk small, see the world around us rather than zoom by it.

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