A Fossil Hoatzin from the Miocene of Colombia

T• rich collections of Miocene vertebrate fossils obtained by Dr. R. A. Stirton and h/s associates in the upper Magdalena Valley of Colombia, South America, have consisted ch/efiy of mammal/an and reptilian mater/al (Stirton, 1951; Savage, 1951). Even though a bat and small primates have been found, bird remains inexplicably are almost lacking. However, in close association with the monkey, Ceb,tpitheca sarraientoi, was part of a skull which when prepared proved to be that of a galliform bird. Further removal of the matrix uncovered many of the fine details of cranial structure which showed that this fossil bird had close affinity with the aberrant galliform type known as the hoatzin, family Opisthocomidae. This family heretofore has been unrepresented in the fossil record. Few groups of birds have the narrow, elongate postorbital cranium lacking high occipital crests which is found in the Galliformes. Some genera of the Tinamiformes have the same general configuration of the cranium, but in all the tinamous examined the suprameatic crest is very differently shaped from that in the Galliformes; it consists of a simple are bearing a down-turned process anteriorly. Also the occipital condyle is a simple, single knob in the Tinamiformes instead of a dorsally cleft process as in the Galliformes. The Miocene fossil shows so many points of similarity to the hoatzin, even in matters of precise location and size of foramina in the orbit, that I have no hesitancy in placing it in the family Opisthoeomidae. It may be described as