SMALL CROCODYLIFORMS FROM THE PROCTOR LAKE DINOSAUR LOCALITY OF CENTRAL TEXAS (TWIN MOUNTAINS FORMATION, LATE APTIAN) AND THEIR PHYLOGENETIC RELATIONSHIPS WITHIN CROCODYLOMORPHA

Within the Twin Mountains Formation, the Proctor Lake dinosaur locality in central Texas has yielded two previously undescribed small-bodied crocodyliforms represented by cranial and post cranial material. The first taxon from Proctor Lake (taxon 1) is distinguished by a unique combination of characters; including an enlarged third maxillary tooth, internal choanae bordered anteriorly by the palatines and by the pterygoids posteriorly and laterally, anterior margin of the choanae situated at the posterior edge of the suborbital fenestrae, a median crest along the midline of the parietal and frontal, and procoelous vertebrae. Taxon 1 represents one of the most derived taxon of non-eusuchian neosuchian in Texas. A phylogenetic analysis recovered this new crocodyliform to be strongly related to the undescribed yet widely discussed ‘Glen Rose form,’ and suggests they are referable to the same genus. A clade comprised of these two taxa plus Shamosuchus and Rugosuchus form a monophyletic group that is the sister clade to Eusuchia within Neosuchia.

The second crocodyliform taxon from Proctor Lake (taxon 2AC) is represented by a single partial skeleton with complete dentary, trough-shaped mandibular symphysis, long limbs, amphicoelous vertebrae, and square dorsal osteoderms. An exploratory phylogenetic analysis recovered taxon 2AC as either basal to the Goniopholididae+ Eusuchia or basal to advanced neosuchians. Together, the Proctor Lake crocodyliforms expand the taxonomic diversity of the Early Cretaceous units of Central Texas and provides insight into the paleoecology of the Proctor Lake dinosaur nesting site.