The skull and skeleton ofEogyrinus attheyiWatson (Amphibia: Labyrinthodontia)

Abstract

As a preliminary to the redescription of the anatomy ofEogyrinus attheyiWatson, an account is given of the problems of nomenclature of British members of the anthracosaur family Eogyrinidae to which it belongs. There is no evidence to show that the four named genera of British eogyrinids differ from one another in any significant feature not explicable by allometric growth. Reconstruction of a series of allometric curves based on known skull specimens allows estimation of the dimensions of incomplete specimens. The skulls then fall into four size groups which correspond, with some stratigraphical backing, to the four named genera. The lectotype skull ofEogyrinus, from the Low Main Seam, Newsham, Northumberland, has been cleaned using an ‘ Airbrasive’ unit and is used as the basis of a new description of the skull. Additional information is provided by other Newsham specimens and two skulls from the Middle Coal Measures of Lanarkshire. The skull is completely known and is typical of anthracosaurs. The skull roof is closely similar to that of the eogyrinidPalaeoherpeton('Palaeogyrinus’)but no anterior tectal bone is present above the naris inEogyrinus. The nature of the dermal ornament is fully described. The palate is typically anthracosaur, with toothless vomers, a ‘ tusk-pair ’ on each palatine and ectopterygoid, and additional small ectopterygoid teeth. The pterygoids descend below the level of the jaw line posteriorly as inPalaeoherpeton. The braincase is reconstructed from an isolated Newsham specimen, originally attributed by Watson, from the lectotype and from one of the Scottish skulls. The isolated specimen shows the course of the semicircular canals as well as the fenestra ovalis. Most of the cranial nerve foramina are present. A complete reconstruction of the lower jaws is possible both as single rami and in articulation. Description of the jaw articulation allows a reconstruction of the relative movements of the rami in opening and closure. The only associated material of the appendicular skeleton is the lectotype left femur, but an interclavicle from Newsham is certainly eogyrinid and probably pertains toEogyrinus. Isolated ventral scales are described and their pattern of articulation reconstructed. The material described in this paper is combined with that used in an earlier account of the axial skeleton to give a reconstruction of the whole skeleton ofEogyrinusin articulation, together with a restoration of the appearance of the living animal.