Old Fishy Bits from the Big Horn Basin of Wyoming

The Bighorn Basin is best known for its Paleocene and Eocene mammal fossils, yet on the highway west of Buffalo an outcrop of early Palaeozoic rocks exhibit a fragmentary record of early fish evolution. In a recent article in Palaeontology (vol. 48) Ivan Samson and M.Paul Smith revisted the site to discover a fauna of late Ordovician jawless fish. The fauna is composed of fragmentary remains of Astraspis and Eroptychius, biostratigraphically constrained by a diverse sample of conodonts. These early fish fragments (osteoderms) enable a better understanding of the paleogeography of the shelf margin of the Williston Basin and the paleoecology of an ancient Ordovician sea.