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1 December 2008 Gerrothorax pulcherrimus from the Upper Triassic Fleming Fjord Formation of East Greenland and a Reassessment of Head Lifting in Temnospondyl Feeding
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Abstract

The plagiosaurine Gerrothorax pulcherrimus, a ubiquitous faunal component of the Fleming Fjord Formation, is recognized by tubercular ornamentation, contact between the postfrontal and supratemporal, 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 posterolateral 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.

Farish A. Jenkins, Neil H. Shubin, Stephen M. Gatesy, and Anne Warren "Gerrothorax pulcherrimus from the Upper Triassic Fleming Fjord Formation of East Greenland and a Reassessment of Head Lifting in Temnospondyl Feeding," Journal of Vertebrate Paleontology 28(4), (1 December 2008). https://doi.org/10.1671/0272-4634-28.4.935
Accepted: 1 March 2008; Published: 1 December 2008
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