The late Miocene Phractocephalus catfish (Siluriformes: Pimelodidae) from Urumaco, Venezuela: additional specimens and reinterpretation as a distinct species

Abstract

Based on additional specimens the fossil pimelodid catfish from the upper Miocene Urumaco Formation, Falcón State, Venezuela originally assigned to the extant species Phractocephalus hemioliopterus is described as a new, extinct species. †Phractocephalus nassi n. sp. is diagnosed by the following combination of characters: 1) posterior half of frontals and anterior half of supraoccipital with elongate, coarse ridges and sulci in addition to reticulating ridges and subcircular pits; 2) very broad and ornamented mesethmoid bone; 3) lateral ethmoid margin convex and eliminating orbital notch but not projecting far anteriorly over palatine condyle; 4) anterior cranial fontanelle closed or represented by a small pit; 5) supraoccipital process rounded laterally and posterolaterally, concave posteriorly and completely concealing Weberian complex in dorsal view; 6) opercle covered with reticulating ridges and pits; 7) cleithrum coarsely ornamented along ventral edge and bulging outward lateral to spine articulation; 8) pectoral spine mostly ornamented with coarse ridges and sulci. †Phractocephalus nassi is compared to modern P. hemioliopterus and an undescribed extinct species from the upper Miocene Solimões Formation, Acre, Brazil. New diagnostic characters of Phractocephalus are presented that apply to the modern and fossil species, including: 1) ornamentation of skull, pectoral girdle and fin spines comprising a coarse meshwork of reticulating ridges surrounding rounded pits plus some elongate ridges and sulci; 2) supraoccipital posterior process greatly expanded laterally and posteriorly behind occipital wall; 3) lateral ethmoid and sphenotic broadly sutured behind eye; 4) anterior cranial fontanelle reduced or completely closed and posterior cranial fontanelle closed; 5) vomerine tooth plate large, roughly pentagonal to triangular in form, and with fine teeth. Today Phractocephalus ranges widely throughout the lowland Orinoco, Amazon and Essequibo basins. However, the genus does not occur west or north of the Andes or Venezuelan coastal ranges. Recognizing the Urumaco Phractocephalus as a distinct species does not alter the obvious conclusion that this catfish marks a large river connection between the Caribbean coastal region and the Orinoco system during at least part of the Neogene. Other Urumaco fossils show this same biogeographic relationship.É descrita uma nova espécie fóssil de bagre pimelodídeo proveniente da Formação Urumaco do Mioceno superior no estado Falcón, Venezuela. O exemplar fóssil foi originalmente atribuído a espécie recente Phractocephalus hemioliopterus. Porém, com base em exemplares fósseis adicionais provenientes da Formação Urumaco, essa espécie extinta é descrita como uma nova espécie. As características diagnósticas da nova espécie †Phractocephalus nassi são as seguintes: 1) a metade posterior do frontal e a metade anterior do supraocciptal apresentam uma ornamentação caracterizada por altos relevos e sulcos alongados, assim como reticulações e algumas depressões subcirculares; 2) o mese...

Biogeography of Amazonian fishes: deconstructing river basins as biogeographic units

“…Such polarity supports the long-recognized importance of the Andean range as a biogeographic barrier, isolating trans-Andean basins from the rest of South American drainages (cf. Eigenmann, 1920Eigenmann, , 1921aEigenmann, , 1921bEigenmann, , 1923Lundberg, Aguilera, 2003;Albert et al, 2006;Rodríguez-Olarte et al, 2011). In all analyses, trans-Andean basins form a monophyletic group, with the Maracaibo basin as sister group to the clade composed of the Atrato + Magdalena.…”

The Oligocene-Miocene Transition on Coral Reefs in the Falcon Basin (Nw Venezuela)

“…This river system would have contained a common freshwater fauna, including fish species represented as fossils in Falcón Basin Miocene rocks and from the Acre region in southwestern Amazonia (Aguilera, 1994;Aguilera and Rodrigues de Aguilera, 2003;Lundberg and Aguilera, 2003;Sánchez-Villagra et al, 2003;Sánchez-Villagra and Clack, 2004;Sánchez-Villagra and Aguilera, 2006;Sabaj Pérez et al, 2007). These fossils include large specimens of the distinctive pimelodid catfish genus Phractocephalus, such as P. nassi from the late Miocene Urumaco Formation in the Falcón Basin (Lundberg and Aguilera, 2003).…”

“…These fossils include large specimens of the distinctive pimelodid catfish genus Phractocephalus, such as P. nassi from the late Miocene Urumaco Formation in the Falcón Basin (Lundberg and Aguilera, 2003). Other fossils from this exclusively freshwater genus have been described from the middle Miocene La Venta fauna of central Colombia (Lundberg, 1997) and late Miocene fluvial sediments of Acre, Brazil (Bocquentin et al, 1997).…”

Patterns of Freshwater Fishes of the Caribbean Versant of Venezuela

“…Early Miocene marine transgressions greatly affected the Caribbean coast. The freshwater proto-Orinoco delta, from which large river fishes such as Phractocephalus and Colossoma are known as fossils was transformed as estuarine and marine environments penetrated far inland and abutted the Andes (LUNDBERG and AGUILERA, 2003;DAHDUL, 2004). The rise of the Mérida range isolated the Lake Maracaibo and Magdalena Basins ALBERT et al, 2006), leaving the region vulnerable to mass extinctions, but also permitted subsequent vicariant speciation.…”