Cranial morphology of Platypterygius longmani Wade, 1990 (Reptilia: Ichthyosauria) from the Lower Cretaceous of Australia

Abstract

Exceptionally well-preserved remains belonging to the Australian Early Cretaceous (Albian) ichthyosaur Platypterygius longmani Wade, 1990 are described in detail. The material is used to reconstruct some of the cranial musculature and provide a brief functional analysis of the skull and mandible. Preparation of specimens using acetic acid and application of high-resolution X-ray computed tomographic analyses has revealed many previously unrecorded anatomical details, including the absence of a coronoid and squamosal, and the presence of well-developed epipterygoid facets on the pterygoid and parietal (possibly indicating retention of an unossified epipterygoid element). Reconstruction of the jaw musculature suggests a well-developed m. adductor mandibulae internus pterygoideus (serving to close the jaws against inertia and drag of the surrounding water), and possibly an m. intramandibularis (acting to accentuate static pressure along the elongate mandible when the jaws were closed). Despite its large size (maximum total body length of around 7 m), the long, narrow snout of P. longmani (together with preserved gut contents) indicates selective feeding on relatively small prey such as fish, small tetrapods and probably cephalopods. Large orbits are indicative of a visual hunter, but extensive external passages for nerves and blood vessels might suggest the presence of a dermal sensory system. The massive stapes appears to have lost all sound conductive function, serving primarily as structural support in the basicranial region. © 2005 The Linnean Society of London.