K-T crocodylians

[MKIRKALDY@aol.com]

Posted for Chris Brochu.
_____

Folks,
    A couple of questions on K-T crocodylians have come up.  Here are
some thoughts:

    1.  Stomatosuchus.  This is a crocodyliform, but may not be a
crocodylian (e.g. not a member of the crown group).  Hard to say, because
(as Adam pointed out), the original material no longer exists.  The lower
jaw may have been edentulous (again, hard to say), but the maxillae and
premaxillae evidently had small teeth.

    This kind of morphotype arose at least twice within the crown group
separately.  Nettosuchids are (primarily) South American caimans; they had
small teeth (though both upper and lower jaws had teeth) and, like
Stomatosuchus, was very large, with a skull exceeding 1 meter in length.
But these are known  only from the Cenozoic.  The other (which was very
large but had very large teeth) was also a Cretaceous beast, but I am not
at liberty to say what this is ;-)

  We have no idea what they ate.  Stomatosuchus and the nettosuchids
were likely not specialized for large-bodied prey - the dental apparatus is
wrong for that.  But that's a speculation.

    Stomatosuchus was from the Cenomanian, and the Mystery Beast is
from the Campanian, so neither are relevant to the issue of KT crocs.

    2.  Survivorship across the KT boundary.  Several  studies (e.g.
Markwick or Vasse and Hua) indicate that crocs were relatively unaffected
by whatever happened, as there was no numerical drop in diversity.  My own
work shows that most Paleocene crocodylians are very close relatives of
Late Maastrichtian taxa, and very few major lineages croaked.  In fact, we
may be looking at metataxa, as some of these Paleocene forms may be direct
descendents of Maastrichtian forms - though as always, we cannot ever
determine whether something is an actual direct descendent of something
else. The big croc extinctions seem to be at the end of the Eocene and end
of the Miocene.

chris

------------------------
Christopher A. Brochu
Assistant Professor
Department of Geoscience
University of Iowa
Iowa City, IA 52242

christopher-brochu@uiowa.edu
319-353-1808 phone
319-335-1821 fax