SVP10 – basal crocs

Drymala 2015 has something to say about basal crocs. Unfortunately, perhaps, not enough.

From the abstract
“Crocodylomorphs were the only crocodile-line archosaurs to survive the end-Triassic extinction event* and parsing out their early evolution is a critical step in studies of post-extinction recovery. Early taxa were terrestrial predators of predominantly small body size that are typically recovered as a paraphyletic grade with respect to Crocodyliformes**. In order to better place all basal crocodylomorph taxa into a phylogenetic context, we have reevaluated the anatomy of several well-known taxa and conducted the first phylogenetic analyses to include newly discovered specimens. We further prepared and reevaluated the holotype specimen of Dromicosuchus in light of newly recovered, more complete early crocodylomorph remains, resulting in revisions to the anatomy as previously described. Certain hind limb materials originally referred to Dromicosuchus are now recognized as aetosaurian. Other elements noted to be absent have been identified, including the interclavical and quadratojugal. Moreover, detailed analysis of several well-preserved specimens (e.g., NCSM 13733, CM 29894, etc.) indicates that parsing out the complex articulations of the antorbital and postorbital regions of basal Crocodylomorpha require scrutiny via computed tomographic (CT) imagery. For example, the maxilla-jugal-lacrimal contact in many taxa appears to be interdigitated and the nature of the quadratojugal may be more laminar and anteroventrally extensive than previously thought. With this new information, we conducted a phylogenetic analysis of 42 taxa (17 crocodylomorph OTUs) and 242 characters (60 MPTs, 651 steps), which resulted in a well-resolved Crocodylomorpha with large-bodied taxa, including the newly named Carnufex carolinensis and the fragmentary Redondavenator, representing the earliest diverging members. The analysis also recovered a basal clade*** composed of Dromicosuchus, Hesperosuchus, and several other specimens, united by a deep, well defined antorbital fossa, and a medial tuber on the proximal head of the radius. Specimens previously referred to “Hesperosuchus” (YPM 41198, CM 29894) did not group together in a clade with the holotype specimen of Hesperosuchus agilis (AMNH 6758). The analysis also found Terrestrisuchus and Dibothrosuchus as sister taxa****. Detailed morphological examination and phylogenetic analysis of basal Crocodylomorpha is essential for our understanding of trait evolution and ecology in Triassic and early Jurassic taxa and in improving outgroup choice in phylogenetic analyses of early Crocodyliformes.”

*Not so. The theropod/bird line also survived.
** Other than the Gracilisuchus and the Pseudhesperosuchus/dinosaur clades, other basal crocs form a monophyletic clade in the large reptile tree.
***Odd that several basal crocs recovered in the large reptile tree are not mentioned here.
**** Not so in the large reptile tree.

References
Drymala S 2015.
New clades and characters in basal crocodylomorph phylogenetics. Journal of Vertebrate Paleontology abstracts.

Leave a Reply

Fill in your details below or click an icon to log in:

WordPress.com Logo

You are commenting using your WordPress.com account. Log Out / Change )

Twitter picture

You are commenting using your Twitter account. Log Out / Change )

Facebook photo

You are commenting using your Facebook account. Log Out / Change )

Google+ photo

You are commenting using your Google+ account. Log Out / Change )

Connecting to %s