A NEW GENUS OF RHOMBODONTIDAE (MYLIOBATIFORMES) FROM THE EOCENE OF WYOMING, U.S.A

Myriad ray teeth have been described from the Upper Cretaceous of Europe and North America, with a complex array of genera and species being the result. Paleogene ray teeth are less common in the fossil record. Here, we document an occurrence of teeth of an early Eocene ray that are quite similar to two Late Cretaceous genera. These ray teeth were recovered from anthills in green shale just above the stratigraphically lowest coquina bed in the Wasatchian Niland Tongue in the Washakie Basin in Wyoming and represent a new genus of rhombodontid ray. These teeth have a variety of interesting features including a lack of highly wrinkled enameloid ridges on the crown faces, a smooth occlusal surface, a root that is the same height or greater than the height of the crown and tooth roots that are smooth and not pitted. This new genus is the second chondrichthyan taxon documented from the Eocene Green River lake system, and is of Atlantic affinity, not the trans-Pacific affinity claimed by some for the Green River fish fauna. Prior to documentation of this new genus, the only selachian known from the Eocene Green River Lake basin were two species of the stingray Heliobatus. This genus is also the youngest rhombodontid, as well as the first known North American rhombodontid.