A new unusual Osteichthyan fish from the Gogo Formation in Western Australia

Abstract

A unique specimen of a braincase and part of the skeleton of an osteichthyan has been etched from limestone in the Gogo Formation (Frasnian) in the Canning Basin, Western Australia. This has been reconstructed using the standard techniques for interpreting nerves and vascular systems, and an abbreviated reconstruction of the main skeletal features, nerves and vascular structures has been presented. This indicates that the pattern falls outside the range of currently known osteichthyan genera, and we consider that it represents a new pattern of structure evolved from a massive change in the genotype, probably by genomic regulatory systems. Interpretation of the bony skeleton is described using standard observational techniques and serial tomography. The dorsal skull roof consists of a posterior undivided plate with a pointed anterior projection. Ventral to this is another internal support plate attached to the dorsal plate posteriorly and laterally, and medially by vertical stubs. Orbits occur in dorso-anterior position. Strong median ridge ventrally runs anteriorly, and it joins an internasal cartilage. Antero-lateral to the braincase is a large cavity thought to be filled with cartilage in life, and lateral to that and separated from it by a bony sheet, is another cartilage filled space. All these skeletal features are diagnostic of the character of a new group of organisms.