Some time ago, Nora Bryan wrote about the difficulty of distinguishing
limpet scars from bite marks on fossil ammonites. Erle Kaufmann interpreted
the holes as punctures made by mosasaurs in the 1960's. Recently, Kase and
others (including Dolf Seilacher) convincingly showed that some holes on
ammonites are limpet scars in:
 
Kase, T., Johnston, P. A., Seilacher, A. & Boyce, J. B. 1998. Alleged
mosasaur bite marks on Late Cretaceous ammonites are limpet
(patellogastropod) home scars. Geology, 26(10): 947-950.
 
What you have to realize is that the eminent researchers did not study the
same ammonites, though they did work on specimens from the same age and
formation. Seilacher wanted to examine Kaufmann's ammonite, but this
specimen was lost several years ago, so it is no longer available for
study. If it has mosasaur bite marks, no one can tell for sure now. It
could be that they are both right in different cases. As Walt Whitman said
(more or less), "And if I contradict myself, very well, I contradict
myself. I am large; I contain multitudes." Nature might say the same.
 
David Schwimmer (the REAL vertebrate paleontologist living in Columbus,
Georgia, not the actor on "Friends") has documented bite marks of sharks in
Cretaceous dinosaur bones. He can distinguish marks made in "green" bone
(that is, fresh bone) and in old, brittle bone. As to whether sharks made
the holes, he has excellent evidence: Some of the holes have shark teeth in
them. Sharks shed their teeth frequently and they sometimes rip out while
they are feeding.
 
Andrew K. Rindsberg
Geological Survey of Alabama
Tuscaloosa, Alabama, USA