Monday, September 22, 2008

Proterosuchus? I Guess Not.

Apparently, Proterosuchus is not considered a basal Archosauria proper. I got the idea that it WAS thanks to my Dinosauria, 2nd Edition, but then I read on Chinleana that it's NOT. Rather, it's a non-archosaurian archosaurmorph. Makes me angry. I thought I was done with the stupid art show. So, okay readers, please point me toward an archosaur (preferably basal to the Crurotarsian-Ornithodiran split) that has an obvious antorbital fenestra and maxillary fenestra, because those are the features we're focusing on in the show's introductory text.


And hey, what's the current status of Euparkeria? According to the list of Archosauria synapomorphies in Dinosauria, 2nd Edition, it seems like that little guy would fit. Here is the list, according to the book:

1) An antorbital fenestrae;
2) The postfrontal reduced to less than half the dimensions of the postorbital or absent;
3) An ossified laterosphenoid;
4) The prootic midline contact on the endocranial cavity floor;
5) Teeth with serrated margins;
6) A lateral mandibular fenestra

Since Euparkeria has features 1, 5, and 6, I'm guessing it lacks features 2, 3, and/or 4. I was surprised to learn that the fourth trochanter is diagnostic of a more inclusive group and thus not a synapomorphy of the Archosauria, proper.


Christopher Taylor said...

The base of Archosauria is generally defined these days as the junction of Crurotarsi and Ornithodira, so by definition there cannot be an archosaur outside the Crurotarsi-Ornithodira split. However, older texts generally included a number of basal forms in Archosauria that are just outside the split - such as Proterosuchus.

Nick Gardner said...

You better be doing some fucking awesome crocs.

Zachary said...

Tryin', brother. Stomatosuchus, Simosuchus, Desmatosuchus, Effigia, Arizonasaurus. Very few ornithodirs, actually. Three pterosaurs just to show the diversity of the group, and three dinosaurs to show their diversity, too. And a bird.

Adam Yates said...

Your confusion re. the literature is the result of conflict between different definitions. The label Archosauria used to encompass all reptiles that had an antorbital fenestra, and external mandibular fenestra and thecodont teeth. The basal most member of this clade is Proterosuchus. However the first explicit PN definition of Archosauria went with the crown-clade, ie. all descendants of the common ancestor of crocs and birds. This has more or less stuck even though the rationale for jiggering with traditional archosaur content was not very strong. Some people (most notably Dave Gower and Mike Benton) steadfastly refuse to use the redefinition of Archosauria - hence the conflict in the literature. Euparkeria is not a crown clade archosaur but it is very close. Indeed but for a few fiddling little autapomorphies is pretty close to what the common ancestor of the crown clade would have looked like.

Bill Parker said...


Thanks for clarifying. I guess that I should put a disclaimer in that I use the crown-clade definition instead of Avesuchia (Benton's name for the crown clade).

Nick Gardner said...

" Very few ornithodirs"

Omph, just now noticed this. It's "ornithodiran". Sometimes I've seen "ornithodire", but "ornithodiran" beats that out on Google Scholar search 44 to 1 (the only result for the former is Dave Peters's paper in Rivista Italiana di Paleontologia e Stratigrafia).


Zachary said...

I've seen a lot of different spellings of it. Personally, I hate "ornithodirs," because it seems unfinished. I much prefer "ornithodirans," and I'm gonna start using that!

Christopher Taylor said...

Technically, there's no such thing as an "official" way to form vernacular derivatives of technical names, so spell it however you damn well like :-).