Opisthocomidae

Opisthocomidae is a family of birds, the only named family within the order Opisthocomiformes. The only living representative is the hoatzin (Opisthocomus hoazin) which lives in the Amazon and the Orinoco delta in South America. Several fossil species have been identified, including one from Africa<ref name=":0">Template:Cite journal</ref> and one from Europe.<ref name=Protoazins/>

Phylogeny

The phylogeny below is based on the work of Hughes & Baker 1999<ref name=":1">Template:Cite journal</ref> and Mayr & De Pietri 2014.<ref name=Protoazins /> Traditionally classified among the fowl-like birds (Galliformes), recent studies have favored Opisthocomidae's placement within the Neoaves.<ref name=":1" />

Taxonomy

• Family Opisthocomidae Swainson 1837<ref name="mikko">Mikko's Phylogeny Archive [1] Template:Cite web</ref>
  • Genus ?†Foro Olson 1992 (mid-Eocene, USA) - cuculiform?
    • Species †Foro panarium Olson 1992
  • Genus ?†Onychopteryx Cracraft 1971 (Early Eocene of Argentina) – falconid? A nomen dubium
    • Species †Onychopteryx simpsoni Cracraft 1971
  • Genus †Protoazin Mayr & De Pietri 2014 (late Eocene of France)
    • Species †Protoazin parisiensis Mayr & De Pietri 2014
  • Genus †Namibiavis Mourer-Chauviré 2003 (Middle Miocene of Namibia)
    • Species †Namibiavis senutae Mourer-Chauviré 2003
  • Genus †Hoazinavis Alvarenga, Mayr & Mourer-Chauviré 2011 (Late Oligocene and Early Miocene of Brazil)
    • Species †Hoazinavis lacustris Alvarenga, Mayr & Mourer-Chauviré 2011
  • Genus †Hoazinoides Miller 1953 (middle Miocene of Colombia)
    • Species †Hoazinoides magdalenae Miller 1953
  • Genus Opisthocomus Illiger 1811
    • Species Opisthocomus hoazin (Müller 1776) Illiger 1811 [Phasianus hoazin Müller 1776]

Description

The only living representative is the hoatzin (Opisthocomus hoazin), which lives in the Amazon and the Orinoco delta in South America.<ref name="Protoazins" /> Several fossil species have been identified, including one from Africa<ref name=":0" /> and one from Europe.<ref name="Protoazins" />

The hoatzin is a stunning, colourful bird from South America.<ref name=":2">Template:Cite web</ref> The hoatzin is found in the rainforest of the Amazon.<ref name=":3">Template:Cite web</ref> It has a long, permanently erected crest which gives the species a distinctive 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.<ref name=":2" /> The nest is a flat platform in bush or tree above water. The chicks are semi-precocial and leave the nest at about two to three weeks of age.<ref name=":2" /> 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.<ref name=":2" /> The young nestlings can jump out into the water, and swim with wings and feet, in order to escape predators at nest.<ref name=":2" /> Hoatzin embryos are known to develop very quickly compared to other birds.

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The hoatzin lives in tropical forested wetlands of 200 to 500 meters elevation.<ref name=":0" /> The hoatzin is an arboreal species and is folivorous, feeding on leaves, flowers and fruits of a small number of plant species.<ref name="Protoazins" /><ref name=":3" /> It has a large crop that uses bacteria to break down the leaves that it eats.<ref name=":3" /> The hoatzin is unique because it has bacteria in its crop that breaks down its food while it is still in the crop.<ref>Template:Cite journal</ref><ref>Template:Cite journal</ref><ref>Template:Cite journal</ref> This is a process called foregut fermentation.<ref name=":3" /><ref>Template:Cite journal</ref> It rarely drinks because its diet is high in water.<ref name=":3" /> The hoatzin is sedentary and widespread in suitable habitat. They are noisy birds, calling in unison, uttering large numbers of varied sounds.<ref name=":2" />

In addition to foregut fermentation, the hoatzin has 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.<ref name=":1" />