Hoatzin fossil discoveries

This video is called Hoatzin (Opisthocomus hoazin).

New fossil findings shed light on the origins of the mysterious hoatzin

The birds floated across the Atlantic…

October 2011: The bizarre looking South American hoatzin has African origins, according an international team of ornithologists who have studied fossil relatives of the bird.

The hoatzin is a funny old bird: a poor flyer, the chicks are 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 it is its purely vegetarian diet. Digestion does not only take place in the stomach but also in a greatly enlarged crop, where bacteria help to decompose the food. The digestive system of the hoatzins is reminiscent of that of a mammalian ruminant.

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.

Now a team consisting of German, Brazilian and French researchers, including ornithologist Gerald Mayr, has not only described the earliest known fossil find of the mysterious bird group, but has also produced the first proof outside of South America.

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.

As well as the Brazilian findings the researchers also examined 17 million-year-old bones from Namibia. Until now the African fossil finds, described a few years ago as Namibiavis senutae, were allocated to an extinct family of cranes. ‘This allocation can no longer be supported, because the finds demonstrate characteristic bone features of hoatzins,’ explains Mr Mayr.

When two related animal groups are discovered on different continents, two explanations are available – either that the continents were once connected by land, or that distribution took place across the water. Africa and South America were once part of a supercontinent called Gondwana, but this had already broken up much longer than 20 million years ago, the continents being separated by the Atlantic. So hoatzins must have crossed the ocean at some stage in order to get from one continent to the other.

But how does a bird, especially such a poor long-distance flyer, manage to cross a sea more than 1,000 km wide? Even if the flying capabilities of the hoatzin’s ancestors were better, it is highly unlikely that they could have managed this distance in the air.

‘We assume that the bird crossed the Atlantic upon drifting flotsam,’ said Mr Mayr. This means of travel is familiar with regard to some primates, rodents and lizards, but it would be the first proof of a similar journey by a bird.