Pholiderpeton scutigerum Huxley, an amphibian from the Yorkshire coal measures

Abstract

Pholiderpeton scutigerum is an eogyrinid amphibian from the Coal Measures of Yorkshire (Westphalian A). The holotype has been prepared by airbrasive and dental-mallet techniques to reveal the most completely preserved of British embolomeres. The skull and braincase morphology of Pholiderpeton is closely similar to that of Eogyrinus but has provided new information about many of the skull roofing bones and palate, in particular the pterygoid-epipterygoid complex. The braincase has augmented information gained from other embolomere specimens and a new reconstruction has been attempted. A supraoccipital was not present but the otic capsule was roofed dorsally by the opisthotics, as in loxommatids. Study of jaw function in Pholiderpeton suggests that it did not conform to a pure ‘kinetic inertial’ system but that it was essentially unspecialized. The so-called ‘kinetic line’ at the junction of the eogyrinid skull table and cheek was not mobile but was probably a butt joint to resist vertical compression generated during jaw closure. Present on the specimen, and previously undescribed in eogyrinids, were elements of the cervical region, including the atlas neural arch and pleurocentrum, the axis neural arch and rib as well as the pectoral girdle and forelimb, allowing reconstruction of these regions to be made. The eogyrinids resemble Archeria in the structure of pectoral limb and girdle. Forelimb function in Pholiderpeton was more flexible than that proposed for the related Proterogyrinus . The evidence suggests that the eogyrinids, like the archeriids, were long-bodied with a presacral count of 40. The cervical region of embolomeres shows some similarities with that of Proterogyrinus but with a more fully ossified atlas pleurocentrum. The atlas vertebra is also compared with that of Archeria , previously undescribed. A study of the skull table in the genus Archeria is included to assist in taxonomic studies of eogyrinids. A number of consistent characters were found to exist in this region within one species of embolomere. The genus Pholiderpeton Huxley (1869) is shown to be synonymous with Eogyrinus Watson (1926) and therefore takes nomenclatural priority, but it may be distinguished from the related Palaeoherpeton on a number of characters. The isolated skull table pertaining to Pteroplax is not that of an eogyrinid, and is removed from the family. It shows resemblances to Archeria and Proterogyrinus . The North American eogyrinids are retained within the family Eogyrinidae. The family Eogyrinidae is most closely related to the monogeneric family Anthracosauridae, and together these two form the sister-group of the Archeriidae. The Proterogyrinidae is the sister-group of all three, and together these families form the group Embolomeri. A cladogram to express these relationships is presented.