A PROBABLE NEW SPECIES OF PTEROSAUR FROM THE BREAKFAST BENCH INTERVAL OF THE UPPERMOST MORRISON FORMATION AT COMO BLUFF, WYOMING WITH A DISCUSSION OF THE BIOCHRONOLOGICAL STAGE OF THIS UNIT

The Breakfast Bench Interval (BBI) is the highest bone-bearing unit in the Morrison Formation of Wyoming. Cherts, limestones, graded conglomerates, and drab smectitic mudstones document lakes, swamps, floodplains, and episodic channels in the BBI. The BBI fauna suggests a later biochronological stage than that of the classic dinosaur-mammal Morrison beds: 1) The BBI turtles share derived features with Dorsetochelys from the lowest Cretaceous. 2) The BBI choristodere is far closer to taxa from the Lower Cretaceous than it is to Cteniogenys in the levels below. 3) The BBI lungfish include a large form with sharp crests, much like a fish at the top of the Morrison in Colorado. 4) BBI triconodonts show a derived condition in possessing more equally developed main cusps than those in species from the classic Morrison. 5) The peculiar multituberculate Zofiabaatar shares a derived jaw joint with Cretaceous taxa.

Bakker (1998) reported a dentary fragment from Bernice Quarry with five teeth in place, probably from the posterior end of the tooth row. The teeth of the BBI jaw have labiolingually-compressed crowns with elliptical cross-sections, traits also found in istiodactylids. However, the BBI teeth differ from istiodactylids in that the crowns are strongly bent and incurved. Labiolingually-compressed teeth also are known from boreopterids, other ornithocheiroids, and dsungaripterids, though none described match the geometry of the BBI specimen. The spacing between alveoli is larger than in istiodactylids, but is similar to the condition in dsungaripterids and some ornithocheiroids. Several pterosaur elements have been discovered in association with the jaw. Most, and perhaps all, BBI pterosaur bones seem to belong to one species. The distal humerus resembles that of Dsungaripterus in general shape, but differs in several details. The left femur is slender and slightly curved with a deep fossa on its posterior end as in Dsungaripterus.

The femur and humerus suggest possible dsungaripterid affinities; however, these bones have thin walls, which is unlike the condition in dsungaripterids. This monofenestratan pterosaur does not resemble the pterosaurs known from the Morrison Formation. The possession of bent, incurved teeth are novel features in Pterosauria, and suggest that the BBI pterosaur is most likely a new species.