The hoatzin (Opisthocomus hoazin)

With respect to other material evidence, an undisputed fossil record of a close hoatzin relative is specimen UCMP 42823, a single cranium backside. It is of Miocene origin[note 2] and was recovered in the upper Magdalena River Valley, Colombia in the well known fauna of La Venta. This has been placed into a distinct, less derived genus, Hoazinoides, but clearly would be placed into the same family as the extant species. It markedly differs in that the cranium of the living hoatzin is characteristic, being much domed, rounded, and shortened, and that these autapomorphies were less pronounced in the Miocene bird. Miller discussed these findings in the light of the supposed affiliation of the hoatzins and the Galliformes, which was the favored hypothesis at that time, but had been controversial almost since its inception. He cautioned, however, "that Hoazinoides by no means establishes a phyletic junction point with other galliforms" for obvious reasons, as we know today.