Late Devonian tetrapod remains from Red Hill, Pennsylvania, USA: how much diversity?

The remains of Late Devonian tetrapods from the Red Hill locality in Pennsylvania help to elucidate the early stages of tetrapod evolution. Red Hill is a particularly informative site that preserves a diverse fauna and flora within a depositional setting suggesting penecontemporaneous deposition of locally derived material. Here, for the first time, we report on the full suite of early tetrapod remains from Red Hill and consider the implications for tetrapod diversity within the Red Hill ecosystem. Previously described material is reviewed and considered in relation to newly reported specimens. New material described includes isolated skull elements (two jugals, a postorbital, a lacrimal and a coronoid) and postcranial elements (a femur and a gastral scale). The characteristics of many of the Red Hill tetrapod specimens conform to the morphological expectations of Late Devonian forms. Several elements, however, illustrate more derived characteristics and strongly suggest the presence of the oldest known whatcheeriid-like tetrapod. This study demonstrates the difficulty in making taxonomic associations with isolated remains, even when found in close proximity to one another. Exploration of the characteristics of each element, however, demonstrates the presence of at least three early tetrapod taxa at the Red Hill site.