Thursday, July 11, 2019

[Paleontology • 2019] Scolomastax sahlsteini • An Enigmatic Small Neosuchian Crocodyliform from the Woodbine Formation of Texas

 Scolomastax sahlsteini 
Noto, Drumheller, Adams & Turner, 2019

 DOI: 10.1002/ar.24174

New discoveries at the Arlington Archosaur Site (AAS), a Cenomanian (Late Cretaceous) locality in north‐central Texas, are filling gaps in our knowledge of mid‐Cretaceous Appalachian ecosystems, which remain poorly characterized. The AAS is notable because it preserves a diverse crocodyliform record. As seen in other sites that preserve four or more crocodyliform taxa, the species present at the AAS exhibit different snout shapes and body sizes, indicating that this high diversity of sympatric species was likely sustainable due to niche partitioning. Here we describe Scolomastax sahlsteini gen. et sp. nov.a new species of crocodyliform from the AAS, currently known from a partial right mandibular ramus. This species differs from other crocodyliforms in possessing features associated with durophagy or omnivory, including a shortened mandible, reduced tooth count, heterodonty, a dorsally expanded surangular, and enlarged attachments for jaw adductor muscles. Our phylogenetic analysis places this new taxon within Eusuchia as a member of Paralligatoridae and sister taxon to Paralligator gradilifrons. Scolomastax sahlsteini extends the record of paralligatorids into the Late Cretaceous of North America. This discovery represents the first appearance of this clade on the poorly known landmass of Appalachia, supporting a biogeographic connection between North America and Asia in the Early Cretaceous prior to completion of the Western Interior Seaway. However, relationships among other endemic crocodyliforms and tree instability within Paralligatoridae suggest further analysis is needed to resolve phylogenetic and biogeographic relationships

Keywords: Crocodyliformes, Paralligatoridae, paleoecology, niche partitioning, Cenomanian

Systematic Paleontology
Crocodyliformes (Hay, 1930).
Mesoeucrocodylia (Whetstone and Whybrow, 1983).

Neosuchia (Benton and Clark, 1988).
Paralligatoridae (Konzhukova, 1954).

Genus Scolomastax nov.

Type species: Scolomastax sahlsteini, sp. nov.

Etymology: Derived from the Greek words scolos meaning anything pointed, and mastax meaning jaws or mouth; in reference to the tapered anterior dentary, which would have made a pointed, V‐shaped mandible in ventral view.

Scolomastax sahlsteini, sp. nov.

Etymology: In honor of Arthur Sahlstein, who co‐discovered the AAS and discovered the holotype specimen, recognizing his invaluable contributions to this project since its inception.

Holotype: DMNH 2013‐07‐1256, a partial right mandibular ramus.

Type locality and horizon: The AAS, city of Arlington, Tarrant County, Texas. Upper Cretaceous (Cenomanian) Woodbine Formation. Exact locality data are on file with the Perot Museum of Nature and Science in Dallas, Texas.

Diagnosis: A paralligatorid crocodyliform differing from other known paralligatorids in having the following combination of characters (* denotes an autapomorphy relative to other paralligatorids): elongate mandibular symphysis with an anteroposterior length three times its dorsoventral height; splenial participation in the symphysis; dorsal expansion on the anterodorsal surangular, creating a process that makes half the total dorsoventral height of the mandible*; no external mandibular fenestra; rugose, anteroposteriorly oriented ridge on the ventrolateral surface of the angular; large, dorsally directed flange on medial portion of angular*; 10–11 alveoli; anterior teeth mildly procumbent; heterodont dentition, with smaller circular alveoli anteriorly, becoming enlarged and labiolingually wide posteriorly*; two waves of tooth enlargement, with the tenth alveolus the largest followed by the third.

Christopher R. Noto, Stephanie K. Drumheller, Thomas L. Adams and Alan H. Turner. 2019. An Enigmatic Small Neosuchian Crocodyliform from the Woodbine Formation of Texas. The Anatomical Record. DOI: 10.1002/ar.24174

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