A PRELIMINARY REPORT ON BIOSTRATIGRAPHY OF CRETACEOUS FRESHWATER RAYS, WAHWEAP FORMATION AND JOHN HENRY MEMBER OF THE STRAIGHT CLIFFS FORMATION, SOUTHERN UTAH

Isolated ray teeth are commonly recovered in screen washing of Cretaceous rocks, yet little biostratigraphic significance has generally been attributed to these specimens. Abundant freshwater ray teeth found within the Cretaceous sedimentary deposits of southern Utah potentially permit freshwater rays to be used as biostratigraphic tools. The tooth morphology of two new species of cf. Myledaphus found in the Wahweap Formation (Lower Campanian) and the John Henry Member of the Straight Cliffs Formation (Santonian) vary in size, and in crown height to root depth ratio as well as the lingual/labial root displacement. These species of cf. Myledaphus are similar to a species of Myledaphus described from the Milk River Formation of Alberta. The numerous specimens group into two distinct samples suggesting the presence of two species of Myledaphus, rather than variation within a single taxon. Statistical analysis has shown that the rays from the John Henry Member have a crown that is less deep than the root, while the condition in rays recovered from the Wahweap Formation is the opposite. Rays from the John Henry Member also have a blocky crown while those from the Wahweap Formation have a rounder, more bulbous crown. This suggests that isolated ray teeth may biostratigraphically distinguish the Wahweap Formation and the John Henry Member and may be of utility in Cretaceous biostratigraphy.