HILTON, E.J.: Morphological Complexity and Simplicity of the Axial Skeleton of Teleostei

Morphological complexity is a difficult and relative term, generally equated with a greater number of parts or the elaboration of a basic structural element. The vertebral skeleton of Teleostei is among the most complex of all vertebrates, with up to thirteen discrete ossifications per body segment (more in some taxa). In this study, I examined fusion among the pre-ural vertebral elements in a broad survey of taxa. In �Ichthyodectiformes centra are spool-shaped elements from which the neural and haemal arches and parapophyses remain separate. In Elopiformes, the haemal arches and caudal neural arches are fused to the centra; the abdominal neural arches remain autogenous and the parapophyses are only partially, if at all, fused to the centra. In basal Osteoglossomorpha all elements except the abdominal neural arches are fused to the centra; in more derived osteoglossomorphs the abdominal neural arches are fused to the centra. In Clupeomorpha, the anterior neural arches and parapophyses remain autogenous. In Cypriniformes, the very anterior neural arches and most of the parapophyses are autogenous, although the anterior vertebral column is greatly elaborated in association with the Weberian apparatus. In more derived teleosts, each vertebra is fused into a single unit – in essence, simplified. With this simplification, however, there is often considerable elaboration (=complexity) of a sort not seen in more basal teleosts. For example, many groups of Percomorpha have independently evolved well-developed zygopophyses and other modifications of the vertebral elements.