Steatornithidae Oilbirds

The Steatornithidae include a single extant species, the frugivorous Oilbird, Steatornis caripensis, which occurs in the northern part of South America. On the basis of a skeleton from the Green River Formation, a fossil stem group representative was described as P. nivea by Olson (1987); as noted in Sect. 12.1, a second specimen from the Green River Formation was misidentified. Olson (1999a) further tentatively assigned the distal and proximal ends of a humerus from the early Eocene of the Nanjemoy Formation in Virginia to Prefica. An earlier tentative identification of oilbirds in the Quercy fissure fillings (Mourer-Chauvire 1982) was based on a cranial portion of a sternum from a late Oligocene deposit. I consider it likely that this specimen belongs to a species of the Archaeotrogonidae, whose sternum has not yet been described (own observation; see also Mourer-Chauvire 2006).

The skull of P. nivea is unknown, but the shape of its mandible is very similar to that of the extant S. caripensis. P. nivea further shares an extremely abbreviated tarsometatarsus and well-developed temporal fossae with the modern Oilbird; as in extant Steatornithidae, the tibiotarsus is only about as long as the carpometacarpus (Olson 1987; Mayr 2005d). P. nivea is smaller than S. capensis and differs in a number of presumably plesiomorphic features, including the presence of two pairs of notches in the caudal margin of the sternum and the lack of fusion between the ilium and the synsacrum. The fossil was classified in a monotypic taxon, Preficinae, by Olson (1987), who hypothesized that it already had a frugivorous diet similar to that of extant Steatornithidae.

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