SVP 2011 (Day 4, Part II): Crocodylomorphs in the Casino

Or "crocodylomorphs in the convention center", if you prefer.  I love alliteration, don't you?

Here it is, one last afternoon of talks.  I planted myself firmly in Technical Session XVIII for this year's round of "croc" talks.  And the crurotarsan branch of the archosaur family tree was just as well represented as their sister clade had been this morning.  By the end of the session, three new crocodylomorphs were described, and some old misconceptions were (hopefully) dispelled.

A Cuban crocodile, Crocodylus rhombifer, basking at the National Zooloigical Park's Reptile Discovery Center.

As for the three new taxa, the first was a basal crocodylomorph from the Late Jurassic of Patagonia that helps shed light on the transformation between typical basal archosaurian skulls and the more derived skulls of crocodyliforms (Pol et al., 2011).  Phylogenetic analysis shows that his new taxa is more closely related to the Crocodyliformes than it is to Sphenosuchia, suggesting that the "crocodyliform braincase" evolved before the origin of Crocodyliformes, and before the other skull modifications of the group.  The second new taxa was described in a talk by Dr. Casey Holliday and based on work he co-authored with Nick Gardner (who gave a talk on the cranial anatomy of Youngina capensis on Wednesday) on a new, giant crocodilian (nicknamed "shield croc") from the Late Cretaceous of Morocco (2011). "Shield croc" is known from very distinct cranial remains that appear to exhibit some type of ornamentation. Examining other fossil taxa and the behavior of living crocodylians has let Holloway to suggest that these ornaments, combined with the presence of deep vascular grooves in the bone, are indicative of a unique display structure and/or thermoregulatory device that is not seen in other crocodyliformes.  The third new taxa was a basal Miocene caimanine from Panama that leads researchers to believe that the Caimaninae originated in the New World Tropics where they can still be found today, rather than outside of the tropics as previous fossil evidence had suggested (Hastings et al., 2011).

A bask of Alligator mississippiensis waiting for feeding time at the Nashville Zoo at Grassmere.

Hearing about new fossil taxa is great, but what about the living crocodylomorphs, represented by the Order Crocodylia: the modern crocodiles, alligators, caimans, and gharial?  These animals are often thought to be relics of a bygone age; animals that have gone unchanged for tens of thousands of years, referred to as "living fossils".  If you haven't heard already, I'm not a huge fan of this terminology. It misleads people into believing that the long, broad snout of a living crocodylian are standard for all crocodylians, past and present.  Modern forms appear to be generalists in form and behavior, that arose unchanged from generalist ancestors.  In reality, modern crocodylians are not generalists at all.  Their ancestors weren't generalists either, and luckily Dr. Chris Brochu was around to tell us why.  According to their recent analysis of morphological data sets, the "generalized" skull shape of extant crocodylians is not an ancestral standard, but rather, independently evolved at least five times within the group from ancestral forms that were actually more specialized (2011).  Which means that ancestral crocodylians looked nothing like their modern counterparts. They probably resembled small bodied alligatoroids, not the giant crocs we are familiar with today. The group's diversity has just been reduced to a point where we assume the living species are representative of the whole. It's actually a little silly to assume that in the first place, because if you look at all of Crocodylomorpha, it's easy to see that diversity is one of the things that clade does best.

Alligator sp. attempts to make a meal out of a pair of Tapirus polkensis at the Eastern Tennessee State University Natural History Museum & Gray Fossil Site (sorry mammal people).

Do these findings, and all of the others presented in these final talks, help dispel the myth of the crocodylian "living fossil"?  I sure hope so.  But regardless, it was still a great session.  My apologies to anyone who wanted to hear about talks on marine mammals and "ungulates", as I did not make it to either of the other closing technical sessions.  But that does not mean that I don't find desmostylians and perissodactyls interesting.  In fact, I think they're swell (even if my photo of the tapirs above does seem to indicate even more bias towards crocodylians).  Next year I'll get to them, I swear.

The enigmatic, "ancient parodox" of a desmostylian, Palaeoparadoxia tabatai, photographed at the American Museum of Natural History.

Referenced Talks

Technical Session XVIII. Presented at the 71st Annual Meeting of the Society of Vertebrate Paleontology, Saturday, 05 November, 2011, from 1:45-4:15PM.


Brochu, C., Turner, A., Allen, F., Wilberg, E. 2011. The myth of the living fossil: Basal crown group relationships, reversing polarities, and restoraation of the ancestral crocodylian. Presented at the 71st Annual Meeting of the Society of Vertebrate Paleontology, Wednesday, 02 November, 2011, at 2:45PM. 

Gardner, N., Bhullar, B., Holliday, C., & O'Keefe, R. 2011. Cranial anatomy in the basal diapsid Youngina capensis and its relevance to higher radiations of Permo-Triassic Neodiapsida. Presented at the 71st Annual Meeting of the Society of Vertebrate Paleontology, Wednesday, 02 November, 2011, at 2:30PM.

Hastings, A., Bloch, J., Rincon, A., MacFadden, B., & Jaramillo, C. 2011. New Primative caimanine (Crocodylia, Alligatoridae) from the Miocene of Panama. Presented at the 71st Annual Meeting of the Society of Vertebrate Paleontology, Saturday, 05 November, 2011, at 2:30PM.

Holiday, C., & Gardner, N. 2011. A new eusuchian crocodyliform with novel cranial integument and the origin of crocodylia. Presented at the 71st Annual Meeting of the Society of Vertebrate Paleontology, Saturday, 05 November, 2011, at 2:00PM.

Pol, D., Rauhut, O., Lecuona, A., &  Leardi, J. 2011. A new basal crocodylomorph from the Late Jurassic of Patagonia and its implications for the evolution of the crocodyliform braincase. Presented at the 71st Annual Meeting of the Society of Vertebrate Paleontology, Saturday, 05 November, 2011, at 1:45PM.