The Hoatzin (Opisthocomus hoazin) is an unusual species of tropical bird found in swamps, riverine forest and mangrove of the Amazon and the Orinoco delta in South America. It is the only member of the family Opisthocomidae.
The taxonomic position of this family has been greatly debated, and is still far from clear. The Hoatzin is arguably the most enigmatic living bird in regard to its phylogenetic relationships. No satisfying evolutionary hypothesis has been proposed, and the situation has actually become worse with the availability of DNA sequence data.
two claws on each wing. When disturbed, the chicks drop into the water to escape predation, then use their clawed wings to climb back to the safety of the nest. This has inevitably led to comparisons to the fossil Archaeopteryx, but the characteristic is rather an autapomorphy, possibly caused by an atavism towards the dinosaurian finger claws; the developmental genetics of which presumably is still present in the avian genome.
