The occipital region in the basal bony fish Erpetoichthys calabaricus (Actinopterygii: Cladistia)

Erpetoichthys calabaricus has unusual cranio-vertebral anatomy, with an occipital centrum forming a component part of the compound basiexoccipital bone, and a 'free-floating' occipital neural arch that differs from accessory arches found in some teleosts. The occipital neural arch bears autapomorphic lateral projections that articulate with small rod-like bones resembling the spatial relationship of parapophyses and ribs, a feature normally restricted to vertebral centra. Based on analyses of cleared and stained specimens, computed tomography and histology, it is hypothesized that the lateral projections and associated rod-shaped bones are structures that share developmental homologies to the unique 'dorsal ribs' of Polypteridae. © 2008 The Authors.