Opisthocomidae

Opisthocomids Temporal range:Late Eocene- Recent, Possible an early origin based onmolecular clock
Hoatzin(Opisthocomus hoazin)
Scientific classification
Domain:	Eukaryota
Kingdom:	Animalia
Phylum:	Chordata
Class:	Aves
Clade:	Passerea
Order:	Opisthocomiformes L'Herminier,1837
Family:	Opisthocomidae Swainson,1837
Genera
?†Foro ?†Onychopteryx †Hoazinoides †Namibiavis †Protoazin †Hoazinavis Opisthocomus
Synonyms
ForatidaeOlson 1992 HoazinoididaeRasmussen 1997 OnychopterygidaeCracraft 1971

Opisthocomidaeis a family ofbirds,the only named family within the orderOpisthocomiformes.The only living representative is thehoatzin(Opisthocomus hoazin) which lives in theAmazonand theOrinoco deltain South America. Several fossil species have been identified, including one from Africaand one from Europe.

Phylogeny

The phylogeny below is based on the work of Hughes & Baker 1999and Mayr & De Pietri 2014.Traditionally classified among the fowl-like birds (Galliformes), recent studies have favored Opisthocomidae's placement within theNeoaves.

	†Namibiavis †Protoazin †Hoazinavis Opisthocomus

Taxonomy

• FamilyOpisthocomidaeSwainson 1837
  • Genus?†ForoOlson 1992(mid-Eocene, USA) - cuculiform?
    • Species †Foro panariumOlson 1992
  • Genus?†OnychopteryxCracraft 1971(Early Eocene of Argentina) – falconid? Anomen dubium
    • Species †Onychopteryx simpsoniCracraft 1971
  • Genus †ProtoazinMayr & De Pietri 2014(late Eocene of France)
    • Species †Protoazin parisiensisMayr & De Pietri 2014
  • Genus †NamibiavisMourer-Chauviré 2003(Middle Miocene of Namibia)
    • Species †Namibiavis senutaeMourer-Chauviré 2003
  • Genus †HoazinavisAlvarenga, Mayr & Mourer-Chauviré 2011(Late Oligocene and Early Miocene of Brazil)
    • Species †Hoazinavis lacustrisAlvarenga, Mayr & Mourer-Chauviré 2011
  • Genus †HoazinoidesMiller 1953(middle Miocene of Colombia)
    • Species †Hoazinoides magdalenaeMiller 1953
  • GenusOpisthocomusIlliger 1811
    • SpeciesOpisthocomus hoazin(Müller 1776) Illiger 1811[Phasianus hoazinMüller 1776]

Description

The only living representative is thehoatzin(Opisthocomus hoazin), which lives in theAmazonand theOrinoco deltain South America.Several fossil species have been identified, including one from Africaand one from Europe.

Thehoatzinis a stunning, colourful bird from South America.The hoatzin is found in the rainforest of the Amazon.It has a long, permanently erected crest which gives the species a stunning silhouette. This gregarious species is often found in groups of more than 40 birds, and up to 100 birds during breeding season which occurs during rainfalls.The nest is a flat platform in bush or tree above water. The chicks aresemi-precocialand leave the nest at about two to three weeks of age.The adults feed them with semi-digested slimy mass from their crops, and the young are fed during the first four or five months of their life.The young nestlings can jump out into the water, and swim with wings and feet, in order to escape predators at nest.Hoatzin embryos are known to develop very quickly compared to other birds.

Thehoatzinlives intropical forestedwetlands of 200 to 500 meters elevation.The hoatzin is anarborealspecies and is folivorous, feeding on leaves, flowers and fruits of a small number of plant species.It has a largecropthat uses bacteria to break down the leaves that it eats.The hoatzin is unique because it has bacteria in its crop that breaks down its food while it is still in the crop.This is a process calledforegut fermentation.It rarely drinks because its diet includes water.The hoatzin is sedentary and widespread in suitable habitat. They are noisy birds, calling in unison, uttering large numbers of varied sounds.

In addition toforegut fermentation,thehoatzinhas a highly modified skeleton to accommodate its large crop, and in the young of this species, wing claws at the wrist joint which are used to climb among the branches of the nest tree.