Paper No. 2
Presentation Time: 8:20 AM
THE FIRST DEVONIAN RECORD OF A WHATCHEERID TETRAPOD (CATSKILL FORMATION; UPPER DEVONIAN)
The Red Hill site in Clinton County, Pennsylvania, is the source of the only Late Devonian tetrapod fossils from North America outside of Greenland. The tetrapod remains recovered to date from the Duncannon Member of the Catskill Formation at Red Hill are isolated skeletal elements, however the diagnosis of each early tetrapod specimen is important for informing issues of diversity, palaeoecology and palaeobiogeography. Two early tetrapod taxa have been named from the site, Hynerpeton bassetti based on pectoral girdle elements and Densignathus rowei from lower jaw material. Each of these Red Hill forms is comparable to Late Devonian tetrapods such as Acanthostega gunnari and Ventastega curonica. The early tetrapod sample from Red Hill also includes isolated skull elements (jugals, postorbital and lacrimal), other lower jaw fragments, and limb elements (humerus and femur), some of which appear more derived than the previously described forms from the site. The postorbital has a pitted dermal ornament, an open lateral line along the ventral flange, and forms a significant part of the posterodorsal margin of the orbit. The lacrimal has deeply pitted ornament with grooves towards the edges, a fimbriate ventral margin, and contributes to the orbital margin. The characteristics of the postorbital and lacrimal support their assignment to the Whatcheeridae, a group of early tetrapods previously known only from the Lower Carboniferous. An isolated femur from Red Hill also compares favorably with Ossinodus pueri, an Early Carboniferous tetrapod from Australia that has been assigned to the Whatcheeridae. These are the first records of whatcheerid tetrapods in the Devonian, and add to the diversity of early tetrapods at Red Hill. Aside from the inherent interest in early tetrapod diversity and distribution, this study provides an interesting exercise in exploring the criteria for association of isolated skeletal elements from a single depositional unit using taphonomic data and morphological features.