Vertebrate fauna from the non-marine facies of the Catskill Formation (Late Devonian) in Pennsylvania.

摘要

Exploration and analysis of vertebrate fossils from the non-marine facies of the Upper Devonian Catskill Formation in Pennsylvania has yielded an abundant and diverse fauna. This diversity includes placoderm, acanthodian, chondrichthyan, actinopterygian, and sarcopterygians fishes, as well as early tetrapods. The tetrapod material represents two new taxa which extend the temporal and geographic range of tetrapods in North America, suggesting that they attained a virtually global equatorial distribution by the end of the Devonian. The shoulder girdle of Hynerpeton bassetti indicates that appendicular mechanisms of support and propulsion were well developed even in the earliest phases of tetrapod history. The lower jaw of a second tetrapod taxon, Densignathus rowei gen. et sp. nov., was recovered from the same locality as Hynerpeton. The contrast between the robust lower jaw of Densignathus and the gracile lower jaw of Hynerpeton suggests that Late Devonian tetrapods were exploiting different niches in the same freshwater ecosystem. A cladistic analysis of Devonian tetrapods has failed to provide a phylogenetic framework for these early forms. A new specimen of pectoral girdle and fin of the rhizodontiform Sauripterus sp. demonstrates that the architecture of early tetrapod limbs, including the presence of digit-like structures, was presaged in some fully-aquatic sarcopterygians. The fine preservation of the new Sauripterus fin allows re-interpretation of the holotype of that taxon. A new taxon of early actinopterygian, Limnomis delaneyi gen. et sp. nov., is described. This new taxon is a generalized lower actinopterygian of "stegotrachelid" grade. The depositional setting suggests that Limnomis lived in large numbers in an overbank pond. Further systematic work on the Catskill fauna, particularly the sample recovered from Red Hill, will inform phylogenetic, biostratigraphic, and biogeographic studies. The Red Hill site will also provide unique insights into the paleoecology of fishes and early tetrapods, and the development of continental ecosystems.