Hoatzins ( Opisthocomus hoazin) live in the Orinoco Basin and the Amazon jungle, in Venezuela, Guyana and Brazil. They are weird birds. Among other things, when they are young they have well-developed claws they use to climb up trees. They lose those claws when they grow up and learn to fly. David Attenborough says in his wonderful The Life of Birds perhaps they show us a bit how Archaeopterix were, how they used their claws.
The DNA of hoatzins have made biologists scratch their head for a long time. They have classified the animal into its own family and order.