Friday, July 12, 2019

[Paleontology • 2019] Tarsomordeo winkleri • Small Terrestrial Crocodyliform from the Lower Cretaceous (late Aptian) of central Texas and Its Implications on the Paleoecology of the Proctor Lake Dinosaur Locality


Tarsomordeo winkleri  Adams, 2019


ABSTRACT
Within the Twin Mountains Formation, the Proctor Lake dinosaur locality in central Texas is distinct from other Early Cretaceous localities by having an abundance of vertebrate fossils representing a low-diversity assemblage. However, it has yielded two small-bodied crocodyliforms, Wannchampsus kirpachi and Tarsomordeo winkleri, gen. et sp. nov. This new species is represented by a single partial skeleton with a complete dentary, trough-shaped mandibular symphysis, amphicoelous vertebrae, nearly square dorsal osteoderms, and gracile, elongated limbs. In addition, limb morphology indicates a parasagittal posture, an attribute for a terrestrial lifestyle that could have allowed T. winkleri to fill an ecological niche as an active predator of nesting dinosaurs and other small prey. A phylogenetic analysis places this new taxon within Eusuchia as a member of Paralligatoridae and the sister taxon to Paralligator major and Rugosuchus nonganensis, providing further evidence for the presence of this clade in North America. This new Proctor Lake crocodyliform expands the taxonomic diversity of the Early Cretaceous units of central Texas and provides additional insight into the paleoecology of the Proctor Lake dinosaur nesting site.


 Comparisons of Tarsomordeo winkleri, gen. et sp. nov., with the maximum size of the Proctor Lake ornithopod, Convolosaurus marri (from Andrzejewski et al., 2019). Scale bar equals 10 cm.

Map of fossil block (SMU field number 2AC) containing the partial skeleton of Tarsomordeo winkleri, gen. et sp. nov., SMU 76870, holotype, from Proctor Lake, Texas. Numbered osteoderms correspond to the order the elements were prepared from the block. White represents elements that have not been identified. Scale bar equals 5 cm.

Interpretive reconstruction of Tarsomordeo winkleri, gen. et sp. nov., showing position of recovered elements discussed in the text. Notosuchus silhouette used as model for reconstruction (phylopic.org). Scale bar equals 10 cm.

SYSTEMATIC PALEONTOLOGY

 CROCODYLIFORMES Hay, 1930 
MESOEUCROCODYLIA Whetstone and Whybrow, 1983 
NEOSUCHIA Benton and Clark, 1988 
PARALLIGATORIDAE Konzhukova, 1954 

TARSOMORDEO, gen. nov.

 Type Species— Tarsomordeo winkleri, sp. nov. 

Etymology—Tarso’ and ‘mordeo,’ derived from the Latin terms for ‘ankle biter’ in reference to the small size of the type specimen. 

TARSOMORDEO WINKLERI, sp. nov.

Etymology— Tarsomordeo winkleri, in honor of Dr. Dale Winkler, for his contributions to the study of Texas paleontology and geology.



Thomas L. Adams. 2019. Small Terrestrial Crocodyliform from the Lower Cretaceous (late Aptian) of central Texas and Its Implications on the Paleoecology of the Proctor Lake Dinosaur Locality. Journal of Vertebrate Paleontology.  e1623226. DOI:  10.1080/02724634.2019.1623226


 Kate A. Andrzejewski, Dale A. Winkler and Louis L. Jacobs. 2019. A New Basal Ornithopod (Dinosauria: Ornithischia) from the Early Cretaceous of Texas.  PLoS ONE 14(3): e0207935. DOI: 10.1371/journal.pone.0207935

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