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Zygodactylidae; Temporal range: Eocene to Middle Miocene
	Primozygodactylus
Scientific classification
Domain:	Eukaryota
Kingdom:	Animalia
Phylum:	Chordata
Class:	Aves
Clade:	Psittacopasseres
Family:	†Zygodactylidae; Brodkorb, 1971
Genera
	†Eozygodactylus; †Primoscens; †Primozygodactylus; †Zygodactylus
Synonyms
	Primoscenidae Mayr 1998

Zygodactylidae is a family of extinct birds found in Europe and North America from the Eocene epoch to the Middle Miocene.^[1] First named in 1971, based on fragmentary remains of two species from Germany, a more complete description of the birds became possible in 2008 when a number of other, better-preserved fossil species were assigned to the family based on a number of shared characteristics.^[2]

The name of the group comes from the presence of a zygodactyl foot, with two toes projecting forward, and two to the rear. This is the same arrangement as seen in living parrots and woodpeckers, and the zygodactylids were at one time thought to be related to the woodpecker family. More recent analyses, however, have shown that they are more likely to be the sister clade to the passerine or "perching" birds, the large clade that includes, among others, all living songbirds.^[3] Passerine birds are distinguished by an anisodactyl foot, but it is thought that their earliest ancestors may have been zygodactyl, likely using this arrangement of toes to cling to the bark of trees as woodpeckers do. Only later did the fourth toe rotate from the rear to face forward in the modern passerine fashion.^[4]

Species

† Family Zygodactylidae

Genus Eozygodactylus, Weidig 2010
- Eozygodactylus americanus, Weidig 2010
Genus Primoscens, Harrison & Walker 1977
- Primoscens minutus, Harrison & Walker 1977
Genus Primozygodactylus, Mayr 1998
- Primozygodactlyus ballmanni, Mayr 1998
- Primozygodactlyus danielsi, Mayr 1998
- Primozygodactlyus eunjooae, Mayr & Zelenkov 2009
- Primozygodactlyus major, Mayr 1998
- Primozygodactlyus quintus, Mayr 2017
Genus Zygodactylus, Ballmann 1969
- Zygodactlyus grandei, Smith, DeBee & Clark 2018
- Zygodactlyus grivensis, Ballmann 1969
- Zygodactlyus ignotus, Ballmann 1969

References

^ Mayr, Gerald (November 2016). "New species of Primozygodactylus from Messel and the ecomorphology and evolutionary significance of early Eocene zygodactylid birds (Aves, Zygodactylidae)". Historical Biology. 29 (7): 875–884. doi:10.1080/08912963.2016.1261135. S2CID 89599089.
^ Mayr, Gerald (2008). "Phylogenetic affinities of the enigmatic avian taxon Zygodactylus based on new material from the Early Oligocene of France". Journal of Systematic Palaeontology. 6 (3): 333–344. Bibcode:2008JSPal...6..333M. doi:10.1017/S1477201907002398. S2CID 84422594.
^ Smith, N. Adam; DeBee, Aj M.; Clarke, Julia A. (June 2018). "Systematics and phylogeny of the Zygodactylidae (Aves, Neognathae) with description of a new species from the early Eocene of Wyoming, USA". PeerJ. 6: 6:e4950. doi:10.7717/peerj.4950. PMC 6022727. PMID 29967716.
^ Reilly, John (2018). The Ascent of Birds. Exeter: Pelagic Publishing. p. 152. ISBN 978-1-78427-203-6.