DISTRIBUTION AND TAPHONOMY OF THE FLYING REPTILE, PTERANODON, FROM THE CAMPANIAN LOWER PIERRE SHALE OF SOUTH DAKOTA

Sediments of the Campanian Lower Pierre Shale in South Dakota contain numerous fossils, including the pterosaur Pteranodon, eighteen of which are now housed at the Museum of Geology at the South Dakota School of Mines and Technology in Rapid City, South Dakota. The basal member of the Pierre Shale, the Gammon Ferruginous Member, is composed mostly of grey mudstone and shale and contains concretions. Two of the eighteen pterosaur specimens were found in this member. A 1 to 1.5 meter thick bentonite succession, the Ardmore Bentonite, marks the lower contact of the Sharon Springs Member with the underlying Gammon Ferruginous Member. The Sharon Springs is a grey to black shale and has produced twelve of the specimens. Overlying the Sharon Springs Member is the Mitten Black Shale Member, which consists of blue-black fissile shale, containing calcareous and siderite concretions, as well as cone-in-cone structures. The Mitten Black Shale Member has produced three specimens.

Eighty-six percent of the South Dakota School of Mines and Technology Museum of Geology’s pterosaur collection consists of wing elements. The remaining percentages of the pterosaur fossils include associated skull fragments, articulated phalanges, scapulae, coracoids, carpals, femora, tibiae, and a part of a basicranium. Two specimens also contain fish vertebrae, which appear to be stomach contents. Two hypotheses explain the abundance of wing elements. The first hypothesis is the existence of a predatory preference. The wing membrane, compared to fleshier body parts, may not offer much to hungry mosasaurs or other predators. The second hypothesis is that the wing membrane would secure the wing elements in place while other elements were free to decompose and fall away, contributing to possible scavenging and breakage. In that case, the wing membrane may have served as a protective layer over the bones until burial.