Only one species of hoatzins exists in South America today - or anywhere else.
Opisthocomus hoazin, also known as the Stinkbird or Canje Pheasant, has an unclear evolutionary history but was assumed to have originated in South America.
Not so, it seems. The oldest known fossils of Hoatzin ancestors reveal that these birds existed around 34 million years ago in Europe, according to paleornithologists at the Senckenberg Gesellschaft für Naturforschung and Flinders University in Adelaide.
The oldest fossils attributed to hoatzins were found more than 100 years ago near Paris but it's only recently that paleornithologists been able to show that these remains belong to ancestors of the modern Hoatzin. The fossils belong to a newly described species, Protoazin parisiensis (“proto-Hoatzin from Paris”).
The re-interpretation of these bones indicates that hoatzins lived in Europe as early as the late Eocene, i.e. around 34 million years ago.
Protoazin parisiensis and Opisthocomus hoazin © Senckenberg
“This supports the theory that hoatzins originated in the Old World,” says Dr Gerald Mayr of the Senckenberg Research Institute in Frankfurt. In the opinion of Dr Vanesa De Pietri of Flinders University in Australia, it is “a further impressive example that the South American avian fauna contains numerous relicts that were once much more widespread”.
Most notably, Hoatzins appear to have become extinct in Europe much earlier than in Africa, where the latest fossils were dated as of Miocene age (15 million years ago) and are thus only around half as old. The disappearance of these birds might be connected to a period when numerous new animal species migrated from Asia to Europe during the so-called “Grande Coupure” around 34 million years ago.
These included tree-dwelling carnivorous mammals who may have posed a threat to hoatzin nestlings, which are raised in open nests. Because hoatzins can fly short distances only, the adult birds are also easy prey. In Africa, by contrast, similar tree-dwelling carnivorous mammals are shown to have existed much later.
The present-day Hoatzin exhibits a special mode of digestion. These herbivores pre-digest their food in this crop before further processing in the stomach and intestines. Similar to the rumen of a cow – a digestive knack that has not been mastered by any other bird. Skeletal features show that Old World hoatzins already had a large crop. Another special feature of the Hoatzin are the claws on the wings of the chicks, which enable the hatchlings to climb trees.
De Pietri, Vanesa L., Mayr, Gerald (2014) Earliest and first Northern Hemispheric hoatzin fossils substantiate Old World origin of “Neotropic endemic”, Naturwissenschaften, Springer-Verlag Berlin Heidelberg 2014 doi:10.1007/s00114-014-1144-8
Mayr, Gerald (2014) A hoatzin fossil from the middle Miocene of Kenya documents the past occurrence of modern-type Opisthocomiformes in Africa. Auk 131: 55-60. doi: 10.1642/AUK-13-134.1
Protoazin Parisiensis: Did South American Hoatzins Originate In Europe?