Osteology and Myology of the Cephalic Region and Pectoral Girdle of Bunocephalus Knerii, and a Discussion on the Phylogenetic Relationships of the Aspredinidae (teleostei: Siluriformes)

The cephalic and pectoral girdle structures of the aspredinid Bunocephalus knerii (Bunocephalinae) are described and compared with those of representatives of the two other aspredinid subfamilies, Aspredo aspredo (Aspredininae) and Xyliphius magdalenae (Hoplomyzontinae), as well as with other catŽ shes. This comparison serves as the foundation for a discussion on the phylogenetic position and autapomorphies of the Aspredinidae. Our observations and comparisons support DE PINNA’S (1996) phylogenetic hypothesis, according to which the Sisoridae of previous authors is a paraphyletic assemblage, with a subunit of it (subsequently named Erethistidae) being more closely related to the Aspredinidae than to the remaining taxa previously allocated to the Sisoridae. In addition, our observations and comparisons pointed out 5 derived characters that are exclusively present in the aspredinid catŽ shes, and constitute Aspredinidae autapomorphies, namely: 1) origin of retractor tentaculi shifted posteriorly, lying medially to the levator arcus palatini; 2) preopercular with a lateral, well-developed, antero-laterally directed expansion of laminar bone extending anteriorly well beyond the remainder of this bone; 3) medial aponeurosis of hyohyoideus abductor Ž rmly attached to the ventral surface of pectoral girdle; 4) pterotic with highly developed, broad postero-dorso-lateral shelf-like expansion of laminar bone extending laterally well beyond the remainder of the proŽ le of the skull; 5) dilatator operculi originated on both the dorso-lateral surface of the neurocranium and the posterior surface of the hyomandibula.