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Re: Terrestrial crocodiles



>chris brochu wrote:
>
>>These aren't "crocodilians" sensu stricto, but are members of
>>Crocodyliformes.  "Sebecosuchians" generally are thought to be primarily
>>terrestrial, though this group is of questionable monophyly.
>
>Hmmm, Chris, what about the gracile Terrestrisuchus? By its name alone, it
>is implied to be a landlubber. Greg Paul depicted it as such (in the book
>"Earth and Life Through Time" or something similarly titled), complete with
>a fully upright pose. Or is it really a crocodyliform?
>


Terrestrisuchus is pretty far removed from living crocodylians - it's a
"sphenosuchian" (an assemblage of questionable monophyly), and as such is a
crocodylomorph, but not a crocodyliform. It's pretty certain that most
non-crocodyliform crocodylomorphs (and most outgroups thereof) were
terrestrial.  Most have argued that basal crocodyliforms ("protosuchians")
were terrestrial, but this is debated (and really not answerable, in my
opinion).

Basically, the former "Crocodilia" used to be an assemblage of varying
membership.  It originally included living crocs and their closest
relatives (the eusuchians) as well as several fossil taxa that lacked
eusuchian hallmark characters (procoelous vertebrae and pterygoidal
choanae) called "mesosuchians."  Sebecosuchians (whether monophyletic or
not) and baurusuchians are "mesosuchians," as is Chimaerasuchus.
"Protosuchians" were added much later, and not everyone agreed that
"sphenosuchians" should be considered crocodilians.  In fact, the meaning
of "crocodilia" fluctuated enough to include things like phytosaurs and
aetosaurs to some people.  We currently restrict Crocodylia to the last
common ancestor of living gavialoids, crocodyloids, and alligatoroids;
Crocodylia + all of the "mesosuchians" = Mesoeucrocodylia, Mesoeucrocodylia
+ "protosuchians" = Crocodyliformes, Crocodyliformes + "sphenosuchians" =
Crocodylomorpha.  (I am aware that Mike Benton's textbook uses one of the
many older uses of "Crocodilia," something I find rather unfortunate for
many reasons.)


I'm at home right now and don't have my references with me - let me know if
anyone wants something to read about these things.




chris



------------------------
Christopher A. Brochu
Department of Geology
Field Museum
1400 S. Lake Shore Drive
Chicago, IL 60605

phone 312-665-7633
fax 312-665-7641
electronic cbrochu@fmppr.fmnh.org