A new cajaro catfish (Siluriformes : Pimelodidae : Phractocephalus) from the Late Miocene of southwestern Amazonia and its relationship to dagger Phractocephalus nassi of the Urumaco Formation

A new fossil species of the living catfish genus Phractocephalus is described from fluvial sediments of late Miocene age in Acre State, Brazil and the Madre de Dios region, Peru. dagger Phractocephalus acreornatus n. sp., is known from a complete neurocranium with associated Weberian complex vertebrae and posttemporal-supracleithra, and several isolated skeletal elements. dagger Phractocephalus acreornatus is diagnosed by the following combination of characters: 1) anterior half of supraoccipital, frontals and sometimes mesethmoid with coarse parallel ridges and sulci in addition to reticulating ridges and subcircular pits; 2) mesethmoid very broad and coarsely ornamented; 3) lateral ethmoid projecting anteriorly above palatine condyle into olfactory capsule, its anterolateral margin convex and fluted, and its orbital notch reduced; 4) supraoccipital process long, concealing Weberian vertebrae in dorsal view; 5) opercle covered with rough, reticulating ridges and pits; 6) interopercle relatively deep, its outer side coarsely ornamented; 7) pectoral spine shaft ornamented with reticulating ridges and pits. Variability of the form of the much expanded supraoccipital process in Phractocephalus is evaluated for its taxonomic significance. Although dagger P. acreornatus is distinct from both modern P. hemioliopterus and fossil dagger P. nassi, like most Miocene fossil fishes from South America, this extinct species is closely similar to its relatives. Available characters provide evidence for a close relationship between dagger P. acreornatus and dagger P. nassi from the Urumaco Formation, Venezuela. The provenance of these late Miocene catfishes in lowland western Amazonia and north-central South America is congruent with paleogeographic models positing a large, north flowing Paleo-Amazon-Orinoco river system in the Andean foreland basin during the Neogene.