Eozygodactylus, Weidig, 2010

Weidig, Ilka, 2010, New Birds from the Lower Eocene Green River Formation, North America, Records of the Australian Museum 62 (1), pp. 29-44 : 36

Eozygodactylus n.gen.

Type species. Eozygodactylus americanus n.gen. and n.sp.

Etymology. Eozygodactylus —Eos Greek for dawn, Zygodactylus —for the zygodactyl foot.

Diagnosis. Within the Zygodactylidae , Eozygodactylus n.gen. is diagnosed as follows: (1) humerus with large processus supracondylaris dorsalis; (2) digitus minoris widens distally; and (3) pelvis with foramen obturatum open.

Character (1) is shared with Zygodactylus and a not yet named specimen from the London Clay held in a private collection (see also below); Eozygodactylus might be congeneric with the latter. Character (2) is autapomorphic for Eozygodactylus . Character (3) is plesiomorphic and also occurs in many other bird taxa such as e.g., Numididae , Charadriidae , Burhinidae , Rallidae , Phoenicopteridae , Threskiornithidae and Coraciidae , but not in Primozygodactylus (the pelvis is unknown for Primoscens and Zygodactylus ).

Differential diagnosis. Eozygodactylus n.gen. differs from: (a) the Eocene Primozygodactylus Mayr, 1998 in: Scapula more strongly curved, humerus with smaller crista bicipitalis, carpometacarpus with larger difference in length between the ossa metacarpalia, sternum relatively longer craniocaudally; (b) the Eocene Primoscens Harrison & Walker, 1977 (the differential diagnosis is not only based on the holotype of Primoscens minutus , which only consists of a carpometacarpus, but also on specimen WN 87558A from the private collection of Michael Daniels that Mayr (1998) referred to the genus Primoscens [for figures, see Mayr, 1998: 78]) in: Humerus with processus supracondylaris (absent in cf. Primoscens ), longer carpometacarpus (8.8 mm in Eozygodactylus versus 6.9 mm in Primoscens ); and (c) the lower Oligocene–Miocene Zygodactylus Ballmann, 1971 in: Coracoid with medium-sized processus procoracoideus (absent in Zygodactylus ), carpometacarpus with less difference in length between the ossa metacarpalia, legs relatively shorter.