Middle Maastrichtian vertebrates (fishes, amphibians, dinosaurs and other reptiles, mammals) from Pajcha Pata (Bolivia). Biostratigraphic, palaeoecologic and palaeobiogeographic implications

The Pajcha Pata fossil locality in south central Bolivia, in the upper part of the Lower Member of the El Molino Formation, is the first late Cretaceo us fauna in South America which has yielded, in addition to some invertebra tes and plants, all kinds of vertebrates except birds, but including dinosa urs and mammals. its middle Maastrichtian age, indicated by geochronologic data, is consistent with the fauna, including the marine ichthyofauna. The vertebrate fossils reported here come from the main fossiliferous level whi ch includes terrestrial, freshwater and marine taxa: vertebrates, Mammalia (both tribosphenic and nontribosphenic therians), Theropoda (Coelurosauria and Sauropoda), Crocodylia, Squamata (Serpentes), Chelonia, Amphibia (Anura , Gymnophiona, Caudata) and fish (Dipnoi, Teleostei, Actinopteri, Cladistia , Chondrostei); invertebrates (Gastropoda, Bryozoa) and plants (charophytes ). Amongst these taxa are the earliest records of some fish, Amphibia and t ribosphenic Mammalia in South America and/or in the world. The fish concern ed are: Polypteriformes (Latinopollia suarezi), Siluriformes of the family Andinichthyidae (Andinichthys) and two new families, Osteoglossiformes of t he subfamily Heterotidinae (Osteoglossidae), Perciformes of the family Lati dae, Dipnoi of the family Lepidosirenidae (Lepidosiren cf. paradoxa). The A mphibia concerned are: indeterminate Gymnophiona, Noterpetontidae (Noterpet on bolivianum). Pajcha Pata is the only known locality in South America wit h both non-tribosphenic and tribosphenic therian mammals. The depositional environment was probably estuarian or lagoonal as indicated by a mixed cont inental, freshwater, and marine fauna. Comparison of this: local fauna with faunas of the same age at localities: belonging to the same proximal part of the El Molino basin on one hand, and with others belonging to the distal part on the other hand, shows that the two continental areas seem to have their own endemic freshwater fish fauna (except the Characidae and the Lepi sosteidae, known in all levels of Bolivia). However, these two areas have t he same marine taxa. This implies some influence of the sea in the whole ba sin. Calculated temperatures of the marine waters rangefrom 13 to 17 degree s for a latitute of about 22 degreesS, implying a southern Pacific upwellin g. The El Molino Basin could have been also connected with the open sea thr ough present-day Argentina and not only Venezuela as thought until now. (C) 2001 Elsevier Science B.V. All rights reserved.