Across the Atlantic On Flotsam: New Fossil Findings Shed Light On the Origins of the Mysterious Bird Hoatzin
ScienceDaily (Oct. 4, 2011) — A team comprising German, Brazilian and French scientists, including an ornithologist from the Senckenberg Research Institute Frankfurt, has examined fossil relatives of the South American Hoatzin(Opisthocomus hoazin), which point to African origins for the enigmatic bird.
Upper arm and shoulder girdle bones, around 23 million years old, from a site in southeast Brazil are the first ever fossil finds of a Hoatzin. The large similarity between the fossils and the corresponding bones of the present-day Hoatzins suggest that the bird developed its unusual nutritional biology at a very early stage. (Credit: © Senckenberg)
The study was published by the journal Naturwissenschaften on October 5.
The Hoatzin is a funny old bird: a poor flyer, the chicks equipped with claws on their wings, it lives on the banks of the Amazon and Orinoco basins in South America. What is particularly unusual about this bird is its purely vegetarian diet. Digestion does not only take place in the stomach but above all in a greatly enlarged crop, where bacteria help to decompose the food. The digestive system of the Hoatzins is very reminiscent of that of a mammalian ruminat.
But not only is the anatomy of the bird unusual; its relationship is still unclear. Since its scientific description in 1776, the Hoatzin has been bracketed alternatively with game birds, cuckoos or the African turacos. However, no relationship with these groups has been proven convincingly until now. For this reason, the bird is usually allocated its own family and genus. The evolutionary origin of the Hoatzins has been unknown so far, and apart from some very fragmentary remains, there were no fossil remnants.
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Out of Africa: Fossils shed light on the origin of the hoatzin, an iconic Neotropic bird
Gerald Mayr, Herculano Alvarenga and Cécile Mourer-Chauviré
We describe the earliest fossils of the enigmatic avian taxon Opisthocomiformes (hoatzins) from the Oligo-Miocene (22–24 mya) of Brazil. The bones, a humerus, scapula and coracoid, closely resemble those of the extant hoatzin, Opisthocomus hoazin. The very similar osteology of the pectoral girdle in the new Brazilian fossil compared to the extant O. hoazin, in which it reflects peculiar feeding adaptations, may indicate that hoatzins had already evolved their highly specialized feeding behavior by the mid-Cenozoic. We further show that Namibiavis senutae from the early Miocene of Namibia is another, previously misclassified representative of Opisthocomiformes, which documents that the extant Neotropic distribution of hoatzins is relictual. Because of the weak flight capabilities of hoatzins, their occurrence on both sides of the South Atlantic is of particular biogeographic interest. We detail that this distribution pattern is best explained by dispersal from Africa to South America, and that Opisthocomiformes provide the first example of transatlantic rafting among birds.
Keywords Opisthocomiformes – Biogeography – Miocene – Brazil – Namibia
Communicated by: Sven Thatje
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