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

["John Hunt" <john.bass@ntlworld.com>]

Surely extant crocodilians could test this.  Some eat mostly fish, some
hardly any.

-----Original Message-----
From: Thomas R. Holtz, Jr. [mailto:tholtz@umd.edu] 
Sent: 24 February 2011 22:53
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