The cranial anatomy of two coal measure Anthracosaurs

Abstract

Amphibian material collected by Mr J. A. Coope from Swanwick Colliery, Derbyshire was developed mechanically and with pyridine. The described remains consist of imperfect skulls of two species of Coal Measure anthracosaurs. The nomenclature of the anthracosaur-type material in the Hancock Museum is discussed and on the basis of this discussion the two Derbyshire skulls are assigned to the speciesPalaeogyrinus decorusWatson andEogyrinus attheyi Watson. ThePalaeogyrinusspecimen is described and, with the aid of redescription of critical regions of the type skull, new restorations of the occiput, the braincase, the skull roof and the palate are produced.Palaeogyrinusis shown to have an open fenestra ovalis of normal tetrapod type, an external naris which cuts the jaw margin, rather like that ofIchthyostega, and an otic notch, which while dorsal in position, is in no sense a continuation of the squamosal-supratemporal joint. TheEogyrinusspecimen shows the articular surface of the squamosal and the posterior palatal structure. Removal of the right pterygoid and extensive epipterygoid revealed details of the braincase including a well-preserved basipterygoid process. The origin of the distinctive anthracosaur pattern of roofing bones is discussed and it is concluded that in this respect these animals are further removed from their fish ancestors than the temnospondyl labyrinthodonts, but that the kinetic separation between squamosal and supratemporal is primitive. The musculature of the jaws is discussed and it is concluded that the characteristic tabular horn was for the origin of the posterior depressor mandibulae rather than a link with the shoulder girdle. The tabular horn together with the absence of post-temporal fossae in the occiput are therefore seen as secondary characters.