Taxonomic Status of the Neogene Snakebird Anhinga fraileyi (Aves, Anhingidae)

Abstract

ANHINGIDAE, commonly known as snakebirds or darters, nowadays is represented by one genus and four species: Anhinga anhinga from southern North America, Central America and South America, Anhinga rufa from Africa, Anhinga melanogaster from southern Asia, and Anhinga novaehollandiae from Australasia (Orta, 1992). From an osteological point of view, An. rufa, An. melanogaster, and An. novaehollandiae can be distinguished from An. anhinga (e.g., Harrison, 1978; Brodkorb and Mourer-Chauviré, 1982; Olson, 1985; Becker, 1986). During the Neogene, the diversity of anhingids in North America was represented by two species (Anhinga subvolans and Anhinga grandis), in Europe by one species (Anhinga pannonica), in Asia by one species (Anhinga sp. cf. An. pannonica), in Africa by three species (Anhinga hadarensis, Anhinga sp. cf. An. pannonica, and Anhinga sp. cf. An. melanogaster) and in Australasia by two species (Anhinga walterbolesi and Anhinga malagurala) (e.g., Olson, 1985; Alvarenga, 1995; Campbell, 1996; Worthy, 2012). In South America during this period the diversity was higher than today and included seven species in four genera: Anhinga hesterna, Anhinga minuta, Anhinga fraileyi, Macranhinga paranensis, Macranhinga ranzii, Meganhinga chilensis, and Giganhinga kiyuensis (Worthy, 2012; Diederle, 2015). In addition, it is likely that Anhinga grandis would also have been present in this continent (Rasmussen and Kay, 1992; Alvarenga and Guilherme, 2003). Most of these Neogene species are known from disarticulated and fragmentary specimens, and there are only a few comparable elements among them. The tarsometatarsi and pelvic girdles are good elements for distinguishing among anhingid taxa, although they are not known for all species. Anhinga fraileyi was originally described by Campbell (1996), based on an almost complete tarsometatarsus collected from the Acre Conglomerate Member of the Madre de Dios Formation, assigned to the Tortonian–Messinian Stage of the late Miocene (Campbell et al., 2001). The fossil horizons crop out along the Acre River in the Madre de Dios Department of Peru (type horizon) and Acre State of Brazil. Noriega and Alvarenga (2002) suggested that An. fraileyi is a species of Macranhinga based on a phylogenetic analysis. Later, Cenizo and Agnolin (2010) cited Anhinga fraileyi as Macranhinga fraileyi, although recent authors (e.g., Louchart et al., 2008; Worthy, 2012; Diederle et al., 2012) have maintained its original combination. Here, I provide a detailed reexamination of the holotype of Anhinga fraileyi, which forms the basis for a new taxonomic proposal. I discuss the implications of this new taxo-nomy for anhingid diversity during the Neogene of South America.