FOSSIL VERTEBRATE DIVERSITY IN ARKANSAS

Arkansas fossil vertebrate diversity is little appreciated, partly as cause and consequence of a dearth of paleontologists working in the state. Yet a rich diversity of fossils offer untapped potential for those that do. Conodonts and graptolites bracketing the base of the vertebrate tree are found throughout the Ouachita Mountains and Ozark Plateau in several Paleozoic age formations. Fish are well represented, especially chondrichthyians, throughout the Phanerozoic. Lamnid sharks, the goblin shark Scapanorynchus, and the actinopterygian fish Enchodus from the Cretaceous Period are common. Of particular note is Ozarcus, a Paleozoic falcatid shark with preserved gill supports. Cretaceous rocks contain a rich reptile fauna, including mosasaurs, plesiosaurs, and turtles. Skeletal material of archosaurs is limited to a goniopholid crocodile, one nonavian dinosaur, Arkansaurus, and one avian, Hesperornis. However, extensive trackways have been found, which have been attributed to titanosaurs and the theropod Acrocanthosaurus. Paleogene reptiles are more limited, but of note is Pterosphenus, an Eocene giant sea snake from the Crow Creek Jackson Group deposits. The Jackson Group also has several mammalian fossils, such as the cimolestid Pantolestes and the whale Basilosaurus. Large Pleistocene mammals are present, including felids such as Smilodon, ursids like Arctodus, canids, artiodactyls, horses, the giant ground sloth Megalonyx, more than twenty mastodons and one mammoth. Small Pleistocene mammals are plentiful, including a variety of musteloids, rodents, rabbits, bats, shrews, moles, and armadillos. Much of the Pleistocene fauna comes from Ozark karst deposits, most notably from Conard Fissure, Peccary Cave, and Hurricane River cave. Arkansas vertebrate fossils are largely poorly studied and offer abundant research and educational opportunities.