A NEW AZHDARCHIFORME PTEROSAUR FROM THE PIERRE SHALE WITH TAPHONOMIC EVIDENCE OF INVERTEBRATE SCAVENGING

GPM 101 is the right wing of a pterosaur consisting of the humerus, radius, ulna, pteroid, two carpals, metacarpal IV, and phalanx I. The specimen was collected from the Pfister Ranch Exposure of the upper Pierre Shale, in Eastern Wyoming. GPM 101 is identified as an azhidarchid based on the form of the humerus, which is unwarped with a proximally curved deltopectoral crest. GPM 101 differs from all previously described azhdarchids in the following combination of traits: a humerus to metacarpal IV length ratio of 1:2.7, a humerus to ulna ratio of 1:1.6, a humerus to phalanx I ratio of 1:3, an underdeveloped deltopectoral crest, a proximal flange spanning from the humeral head to the deltopectoral crest, and a deltopectoral crest and ulnar crest that originate at roughly the same distal position on the humeral shaft. The relative proportions of the various wing elements closely resemble those of the pteranodontian pterosaur Nyctosaurus gracilis, from the older Niobrara Formation. This morphological similarity in two phylogenetically disparate pterosaurs known from sequential deposits of the Western Interior Seaway may reflect ecological niche convergence. GPM 101 shows extensive taphonomic damage from marine mollusks in the form of small 1.1-6.8mm, hemispherical borings. Based on the humeral length, the wingspan of the new azhdarchiforme is estimated at 3.6-5m.