A drepanosaurid pectoral girdle from the Ghost Ranch (Whitaker) Coelophysis Quarry (Chinle Group, Rock Point Formation, Rhaetian), New Mexico

ABSTRACT

An isolated but three-dimensionally preserved pectoral girdle from the Rock Point Formation (Rhaetian) of New Mexico represents the youngest known drepanosaurid. The specimen preserves, in articulation, both scapulae, coracoids, clavicles, and sternal plates; clavicles and sternal plates were previously poorly documented or unknown in the Drepanosauridae. The elongate, thin, dorsally-oriented scapular blades are distinctive autapomorphies of the clade and strongly support the drepanosaurid origin of the specimen. The paired clavicles resemble the furculae of some theropod dinosaurs and basal birds, but the morphology of the remainder of the girdle demonstrates that it cannot belong to either group. The specimen's three dimensional preservation provides new information concerning the pectoral morphology of drepanosaurids.