Phractocephalus hemiliopterus (Pimelodidae, Siluriformes) from the upper Miocene Urumaco Formation, Venezuela: a further case of evolutionary stasis and local extinction among South American fishes

ABSTRACT

A fossil catfish skull from the upper Miocene Urumaco Formation of Falcon State, Venezuela is identified as Phractocephalus hemiliopterus (Pimelodidae), a living species of the large, lowland rivers east of the Andes. This fossil provides another example, in a growing list of cases, of a long and conservative evolutionary history for an advanced South American riverine fish. The phylogenetic position of Phractocephalus implies that other higher level lineages of Pimelodidae had originated before six Ma. This discovery corroborates geological and other biogeographic evidence for a connection of the ancient Orinoco system to the Caribbean coast river systems of Venezuela. The fossil catfish and other large aquatic vertebrates from the same area suggest former, freshwater communities on the north coast that were much richer than modern faunas. Increasing aridity and loss of large permanent rivers in post-Miocene times has presumably caused local extinction of these communities.