GERROTHORAX PULCHERRIMUS FROM THE UPPER TRIASSIC FLEMING FJORD FORMATION OF EAST GREENLAND AND A REASSESSMENT OF HEAD LIFTING IN TEMNOSPONDYL FEEDING

摘要

The plagiosauiine Gerrothorax pulcherrimus, a ubiquitous faunal component of the Fleming Fjord Formation, is recognized by tubercular ornamentation, contact between the postfrontal and supratempoial, at least two tooth rows on the posterior coronoid, and a posttemporal fenestra that is small or absent Gerrothorax pulcherrimus also possesses a derived pectoral morphology that includes an interlocking claviculocleithral complex and an interclavicle with paired posteiolateral projections and a transversely truncated posterior margin Gerrothorax pustuloglomeratus is a junior synonym of G pulcherrimus; other Gerrothorax species cannot be differentiated from G pulcherrimus Flat-headed temnospondyls have been interpreted as having achieved a large gape by raising the skull rather than by lowering the jaw No detailed, corroborating anatomical evidence from the atlanto-occipital joint, however, has ever been adduced. In G pulcherrimus the widths of the atlantal and condylar facets are comparable, but dorsoventrally the condylar facets are 45% longer than the comparable dimension of the atlantal facets Elevation of the skull occurred by atlanto-occipital rotation, and was facilitated by a radius of curvature of the dorsal part of the condylar facets that is shorter than that of the inferior part. From a resting, closed mouth position, G. pulcherrimus was capable of elevating the skull through an excursion of approximately 50°, a movement that rotated the quadrate forward and protruded the lower jaw. An elongate, broadly open neural canal in the atlanto-occipital region, and dorsal displacement of the occipital condyles, are related to relieving the spinal medulla of the sharp angular deformation that head lifting might entail.