NEW VERTEBRATE FOSSIL SITES FROM THE CATSKILL FORMATION OF NORTH-CENTRAL PENNSYLVANIA: RECONSTRUCTING LATE DEVONIAN ECOSYSTEMS AND ENVIRONMENTS

Recent widening along the US-15 corridor in north-central Pennsylvania produced well-exposed Catskill Formation outcrops that are suitable for linking Devonian terrestrial ecologies and sedimentary processes. Several vertebrate fossil zones were recently discovered in the Steam Valley and Trout Run areas of northern Lycoming County. Identifiable vertebrate fossil remains at these sites include placoderms (Bothriolepis, Turrisaspis) sarcopterygian fishes (Holoptychius, Eusthenodon, megalicthyids) and Acanthodians (Gyracanthus). Disarticulated scales, plates, and teeth are commonly preserved as fragmentary remains although unabraded scales are present locally. Most vertebrate fossils are preserved as basal lags associated with caliche nodules, mudstone rip-up clasts, and/or plant fossil fragments in lenticular, cross-stratified to horizontally stratified sandstone bodies. These are interpreted as fluvial channel-bar complexes while sharp-based sandstones with mudcracks and rootlets are interpreted as temporary channels (i.e. crevasse channels/splays and chute bars). Channel/splay sandstones crop out among red floodplain mudstones that bear evidence of pedogenic overprinting (rootlets, irregular green mottles/haloes, caliche nodules, pedogenic slickensides) and minor ponded water (laminated green-gray shales/siltstones). Fossil sites in these nearly flat-lying fluvial strata occur in multiple stratigraphic horizons spanning ~180 m of elevation but the duration of geologic time sampled is not well constrained. Fossil assemblages vary in composition between sites, suggesting possible spatial or temporal variations in communities. From a regional perspective, sedimentology and paleontology of the sampled strata are consistent with partitioning of the Catskill aquatic ecosystems. Sampled outcrops in the Trout Run-Steam Valley area are transitional between coastal delta plain strata that typically produce an abundance of cosmopolitan genera (i.e. Bothriolepis, Holoptychius) and upland alluvial plain strata (i.e. Red Hill) that yield both cosmopolitan and unique taxa that may reflect endemism.