NEW MESONYCHIAN DENTITIONS FROM THE PALEOCENE AND EOCENE OF THE BIGHORN BASIN, WYOMING

We figure and describe for the first time several exceptional mesonych ian dental specimens from the late Paleocene-early Eocene Fort Union a nd Willwood formations of the Bighorn Basin, Wyoming. They include thr ee new species of Dissacus, one of late Tiffanian and two of Wasatchia n age, and several virtually complete dentitions of D. praenuntius. Di ssacus longaevus, which is based on a nearly complete but poorly prese rved dentary, lacks diagnostic traits, and is here considered a nomen dubium. Other specimens reported include well-preserved upper and lowe r dentitions of Pachyaena gigantea, the first nearly complete maxillar y dentition of P. gracilis, and a new specimen of the very rare basal Wasatchian Hapalodectes anthracinus. Considerable variation in jaw dep th and canine size among various mesonychians suggests that these anim als may have been sexually dimorphic.