Labidosaurus hamatus

LABIDOSAURUS HAMATUS COPE, 1895

Diagnosis: A single-tooth-rowed captorhinid distinguished by the following features: extreme angulation of the alveolar margin of the premaxilla, at roughly 45° to the long axis of the maxillary alveolar margin; a low dorsum sellae; an extensive, thin sagittal flange of the dorsum sellae that deeply invades the retractor pit and sella turcica; lateral exposure of prootic greatly reduced by the stapedial and opisthotic contacts and equal to about one-third of the entire lateral portion of the bone; slender stapes; and a small intermeckelian medius foramen that is bounded anteriorly by a small postsymphysial dorsal extension of the splenial.

Holotype: AMNH 4341 (American Museum of Natural History, New York, NY, USA), a complete skull.

Material examined: CM 73370 (Carnegie Museum of Natural History, Pittsburgh, PA, USA) (formerly ‘UCLA VP 3167’; Vertebrate Palaeontology Collections, University of California, Los Angeles, CA, USA), greater part of an articulated skeleton that includes a complete, undistorted skull with tightly closed mandible; CM 73371 (formerly ‘UCLA VP 3200’), greater part of an articulated skeleton that includes a complete, obliquely compressed skull, with partly detached left and fully detached right mandibular rami; CM 76876, a partial right mandibular ramus; FMNH UR 161 (Field Museum of Natural History, Chicago, IL, USA), a complete skull with detached braincase; MCZ 8727 (Museum of Comparative Zoology, Harvard University, Cambridge, MA, USA), a nearly complete skull that has undergone extreme dorsoventral compression.

Horizon and geographical provenance: Lowermost strata (the ‘Arroyo Formation’ of early literature) of the Clear Fork Group, Texas; Leonardian (= Artinskian), Lower Permian. CM 73370, 73371, and 76876, and FMNH UR 161 were collected by E. C. Olson from his ‘ Labidosaurus pocket’ locality (Coffee Creek, Baylor County, TX, USA). Specific locality data is missing for MCZ 8727, which was collected by ‘Chas. H. Sternberg during 1882 in NW Texas’ (C. Schaff, pers. comm., 2005).