Revision and redescription of the genusAstephus(Siluriformes: Ictaluridae) with a discussion of its phylogenetic relationships

Abstract

ABSTRACT †Astephus antiquus from Eocene Green Formation of Wyoming and Utah is redescribed in detail based on newly obtained material, and the position of †Astephus among Siluriformes is reconsidered. Phylogenetic evaluation of the genus is based on descriptive information from †Astephus antiquus, the only species known by nearly complete specimens and a species that contains the type species for the genus. It was determined that Lundberg's (1970, 1975a) assessment of †Astephus as an ictalurid is the most probable interpretation of available information. Assuming that †Astephus is an ictalurid, there is strong evidence indicating that it is the sister group to a group containing all other members of the family. †Astephus calvus (Cope), the type for the genus (designated by Jordan, 1919), is considered here to be a subjective junior synonym of †Astephus antiquus (Leidy). The only other valid species recognized here as probably belonging in the genus (and probably distinct from †A. antiquus) is †A. resimus Lundberg (1975a), a species known only by a single, nearly complete neurocranium. Available evidence (shape of pelvic girdle, pelvic fin rays, and biogeography) indicates that †Astephus is most closely related to a group containing all extant ictalurid genera. However, †Astephus lacks any known unambiguously unique characters shared by living members of the family. Before stronger evidence can be found, more information on the interrelationships of living catfish families (e.g., what family or families make up the sister group of Ictaluridae?) and more characters uniquely derived for Ictaluridae (some of which may be present in †Astephus) will need to be discovered. †Astephus antiquus is one of the two earliest known North American catfish species that is both represented by nearly complete skeletons and easily integrated into phylogenetic osteological studies of living catfish species. [The other Early Middle Eocene North American catfish species that is as well preserved is †Hypsidoris farsonensis, a species that was phylogenetically reevaluated in Grande (1987).]