CLAESON, Kerin M; University of Massachusetts: THE SKULL OF ERPETOICHTHYS CALABARICUS (ACTINOPTERYGII: POLYPTERIDAE), THE ROPEFISH

Polypterid fishes are considered the most basal group of extant actinopterygians and may be a direct link to understanding the systematics and evolution of the first bony fishes. At least 12 extinct and extant genera have been named. Two genera are extant, Polypterus, containing nine species and Erpetoichthys, which is represented by the species E. calabaricus. E. calabaricus, is native to Africa but is a popular aquarium fish and readily available through the pet trade. Since Smith first described specimens of E. calabaricus remarkably little work has been done on the species. I present a detailed description of the skull of Erpetoichthys calabaricus as observed through computed micro-tomography scanning and 3D-digital reconstruction. By using CT-scans and modeling, I was able to digitally disarticulate skulls smaller than 2cm in length without destroying the specimen. Holmgren (1928) stated that E. calabaricus was in all details of its cranial osteology the same as Polypterus. Later, Jollie (1984) supported this claim with one noted exception that the subopercle is absent in E. calabaricus. However, this study highlights several differences in the cranial anatomy of E. calabaricus and Polypterus. These differences include, but are not limited to, an overall elongation of the skull roof observable in most elements, the lacrimal and accessory cheek plates are also absent. Internally we see that there is a shortening of the postemporal processes and that the parasphenoid is wider and the posterior process is shorter in E. calabaricus than in Polypterus. Finally, this study is valuable not only for understanding the relationship of Erpetoichthys to Polypterus, but for understanding the relationship of Polypteridae to other basal actinopterygians.