The braincase, mandible and dental structures of the Early Devonian lungfish Dipnorhynchus kurikae from Wee Jasper, New South Wales

Abstract

Dipnorhynchus kurikae Campbell & Barwick was described from the Receptaculites Limestone Member at Wee Jasper. Our new specimens include material of the braincase, the snout, the nasal capsules, the palate and the mandible which were not previously available. The new specimens give new data on the pores in the snout, the arrangement of the soft tissues in the nasal capsule, the growth of the hard tissues on the surface of the dentary, the formation of the hard surface on the palate and the prearticulars, the arrangement of sacculus and the nerves VII, IX and X in the otic region, and the interpretation of the palatoquadrate. The lateral lines on the mandible have been exposed by excavation. Thin sections show that the bone on the overgrowth of the dentary is of the same kind as occurs in the cores of the ridges on the tuberosities and marginal ridges on the palate and prearticular. A thin layer of dentine-like columns which contain no dentine tubules overlie the bony cores. This, and the mode of growth, demonstrate that the dental plates—being made of a bony core—have different patterns of deposition from tooth plates in most later Palaeozoic genera, which are made of dentine. This throws light on the way tooth plates evolved from a dipnorhynchid pattern through a speonesydrionid pattern to true tooth plates. The complex tooth plates of Diabolepis are considered to be independently developed. Ventrally the parasphenoid of Dipnorhynchus kurikae does not divide the pterygoids, but stops short at the posterior end of the pterygoids. The semicircular canals and the superior sinus of the saccular cavity are described from the well-preserved material. In comparison with D. sussmilchi, this species has a number of distinctive features, and is easily recognised as a separate species.