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deinosuchus occurrences



Ladies and Gentlemen,

        A recent discussion on this forum raised the point about the
distribution,  both geographic and temporal, of the big alligatoroid
Deinosuchus.

        As far as I know, all verified occurrences of Deinosuchus are from
the Campanian and Maastrichtian of North America.  We have definite remains
from western Texas (Deinosuchus/Phobosuchus riograndensis), Montana
(Deinosuchus hatcheri), and along the Atlantic coast wherever latest
Cretaceous coastal deposits are preserved, from New Jersey to Alabama.
Whether or not these all represent one species or two is unclear, as
virtually all of this is scrap.  Fortunately, the osteoderms are very
characteristic, so even bone granola can be sufficient to establish the
presence of the taxon.

        It is important to remember just how little we know about
Deinosuchus.  We collected a partial braincase in West Texas last summer,
and there's some new material from Georgia that will answer a lot of
questions, but published material is very fragmentary, and even the new
material is incomplete.  The famous reconstruction everyone has seen - the
big skull with Barnum Brown and associates standing behind - is, as Wann
Langston once described it, a figment of the imagination.  Based on a more
or less complete mandibular ramus at UT Austin, the skull would have been
much less robust and more alligatorlike in general shape.

        I've seen Deinosuchus scutes in estuarine deposits in western
Texas, and based on collected material around the country it seems to have
gotten into a variety of deposits after death.  Most non-alligatorid living
crocs have no hesitation toward brackish or even salty water, so their
presence in a marginal marine setting would not be surprising.

        I describe it as an "alligatoroid" based on what little I've seen -
and I've seen most of it.  The placement of certain openings at the back of
the jaw, coupled with some sutural arrangements on the mandible, indicate a
placement closer to living alligators than to living true crocodiles.  This
does not mean it was an alligator - only that it shared a more recent
common ancestor with alligators than with other living crocs.  Moreover,
the lack of salt tolerance in living alligatorids (note the -ids rather
than -oids) need not apply to their sister taxa, such as Diplocynodon,
proper Leidyosuchus, or (as far as I can tell) Deinosuchus.  This isn't
published yet, and since the available material is so scrappy, I could
easily be wrong.


chris


=-=-=-=-=-=-=-=-=-=-=-=-=-=
Christopher Brochu

Department of Geology
Field Museum of Natural History
Lake Shore Drive at Roosevelt Road
Chicago, IL  60605  USA

cbrochu@fmppr.fmnh.org