Abstract by Paul Stamler
Right Time, Wrong Place: The Mystery of the Hybodont Shark elements in the Yellow Cat Member of the cedar Mountain Formation
Hybodont sharks, based on a dorsal fin spine and several 3D spiral intestines (often misidentified as coprolites), have been recovered near Cisco, Utah. The specimens are from the Early Cretaceous (Aptian) Yellow Cat Member of the Cedar Mountain Formation. This member and interfingering members have been interpreted as fluvial channel and floodplain deposits far from the marine influence. To explain the presence of sharks in strata thought to be freshwater in origin three hypotheses are evaluated: (1) freshwater sharks, (2) anadromous [migration between fresh and salt water], and (3) fluvial salt water wedges from the transgressing Western Interior Seaway. Each hypothesis is evaluated in light of geological and paleontological evidences. New tests of these hypothesis should include a search of coeval strata north of Cisco and the recovery of additional hybodont fossils, especially teeth (which have not yet been discovered) that could help positively identify the species.