Redescription of 'Amyzon' brevipinne and remarks on North American Eocene catostomids (Cypriniformes: Catostomidae)

摘要

The Eocene catostomid fish (Cypriniformes: Catostomidae) from the Allenby Formation, British Columbia, Canada, is reviewed and revised based on recently collected specimens. The fish was originally recognized as a catostomid by Cope in 1893 and described as Amyzon brevipinne. Wilson comprehensively redescribed the species in 1977 based on a large collection. More specimens collected recently brought to light the need for a systematic revision of this species, different from all known Amyzon species in having a narrow frontal bone with elongated orbital notch, shallow and slender infraorbital series, broad opercle, and short and slender rib 4. It differs from the type species Amyzon mentale in having a shorter posteroventral process of the dentary and fewer dorsal fin rays. Given the differences from all known Eocene catostomid species, Amyzon brevipinne is herein assigned to a new genus as Wilsonium brevipinne. Phylogenetically, this species is resolved as the most basal taxon of Catostomidae. The small-sized fluvial specimens of Wilsonium brevipinne represent the first recognized dwarf catostomid species in the fossil record (maximum standard length similar to 84mm). It is also worth noting that Wilsonium gen. nov. differs from all known catostomids in the elongated orbital notch, shallow and slender infraorbital series and non-robust rib 4. These features are seen in some loaches and gyrinchelids.