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RE: What did Spinosaurus eat? New species of Lepidotes found



  I mentioned in my response to David how the lower jaws of theropod dinosaurs 
are under-tested when it comes to biomechanical studies (especially stress 
analyses). While we also study the mechanics of the jaw joint and lower jaw in 
a mechanical, leverage system, this is largely applied only to ornithischians 
in similarity to that of herbivorous mammals. What has NOT been done is to 
subject the mandible of a variety of taxa, including crocs (gharials 
[specialist] and *Crocodilus* [generalist] would be great), a hesperornithiform 
of some sort, a spinosaurid, an abelisaurid, an allosauroid (*Allosaurus 
fragilis*!), even a tyrannosaurid, along with smaller taxa (*Masiakasaurus*, 
*Coelophysis*, and my perennial favorite *Citipati osmolskae*) to various 
biomechanical distortion and stress analyses. What should be done is to load 
the jaws (including the upper jaws) at a variety of directions, rather than 
points along the dental array, such that pulling on the horizontal and in the 
vertical can also be tested. While some of this mechanical analysis for 
mandibles has been done, it has been extremely limited (mostly it has been done 
to test bite strength, and that's not actually important here).

  The main reason for this is that I have a little theory about spinosaurid (or 
spinosaurine) feeding behavior that is, essentially, novel to tetrapods (or at 
least toothed ones) and such data can also help elaborate different methods and 
modes of feeding that have been touched on (head-slamming, jaw-hatchets, 
bone-crushing, etc.).

Cheers,

Jaime A. Headden
The Bite Stuff (site v2)
http://qilong.wordpress.com/

"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 
Backs)





----------------------------------------
> Date: Thu, 24 Feb 2011 17:53:28 -0500
> From: tholtz@umd.edu
> To: tijawi@gmail.com; dinosaur@usc.edu
> Subject: RE: What did Spinosaurus eat? New species of Lepidotes found
>
> > From: owner-DINOSAUR@usc.edu [mailto:owner-DINOSAUR@usc.edu]
> > On Behalf Of Tim Williams
> >
> > OK, I'm a little confused here. The oxygen isotope ratios
> > for _Spinosaurus_ indicate that the body was immersed much of
> > the time.
> > Immersion in
> > water reduces aerial evaporation and therefore decreases
> > enrichment of 18-oxygen in body water. So I'm not sure how
> > the heron analog fits with this.
>
> Actually, that "immersion" argument of Amiot et al. is one of their 
> inferences that is, in my opinion, extremely weak. Diet's
> influence of p-del-18O is very strong. They dismiss diet as the cause of the 
> similarity between crocs and spinosaurs, and the
> disimilarity between spinosaurs and carcharodontosaurs, because spinosaurs 
> and crocs might have had some terrestrial food in their
> diet.
>
> Well, no kidding! Nevertheless, if crocs and spinosaurids both sampled a 
> greater fraction of fish in their diet than did terrestrial
> predators in the same environment, the prediction is that crocs and 
> spinosaurids would shift isotopically in the same direction.
> Which is exactly what we see.
>
> Thomas R. Holtz, Jr.
> Email: tholtz@umd.edu Phone: 301-405-4084
> Office: Centreville 1216
> Senior Lecturer, Vertebrate Paleontology
> Dept. of Geology, University of Maryland
> http://www.geol.umd.edu/~tholtz/
> Fax: 301-314-9661
>
> Faculty Director, Science & Global Change Program, College Park Scholars
> http://www.geol.umd.edu/sgc
> Fax: 301-314-9843
>
> Mailing Address: Thomas R. Holtz, Jr.
> Department of Geology
> Building 237, Room 1117
> University of Maryland
> College Park, MD 20742 USA
>
>