A Large Scaphognathine (Pterosauria: Rhamphorhynchidae) Humerus With A Pneumatic Foramen and Enlarged Condyles from Morrison Formation, Wyoming, With a Discussion of the Implications of Humeral Condyles in Pterosaurs

We describe a large, three-dimensionally preserved pterosaur humerus from Bone Cabin Quarry in the Upper Jurassic Morrison Formation; one of the largest Jurassic pterosaur humeri on record. The tongue-shaped, relatively unconstricted deltopectoral crest suggests it belongs to a member of the clade Scaphognathinae, though humeri of scaphognathines remain poorly described in the literature. Bone Cabin Quarry has also produced the holotype rostrum of a scaphognathine pterosaur, Harpactognathus gentryii, which possesses a similar estimated wingspan of over two meters, so we tentatively refer the Bone Cabin Quarry humerus to this species. The three-dimensional preservation seen is very rare for "rhamphorhynchoid" elements, preserving features typically obscured or obliterated in other specimens. As a result, this humerus reveals potentially useful characters for rhamphorhynchids, particularly scaphognathines. This specimen is noteworthy for its prominent condyles and expanded distal end, which may have implications for functional morphology. The distal encd of the humerus bears a pneumatic foramen, representing the first known occurrence of pneumatization in the appendicular skeleton of non-monofenestratan pterosaurs. This pneumatization may be a function of size and convergent with pterodactyloids, but because most humeri lack well-preserved and visible distal ends, pneumatization in other known taxa of non-pterodactyloid pterosaurs cannot be explicitly ruled out.