Foro panarium is an extinct bird of disputed taxonomic status that lived during the early to mid-Eocene around the Ypresian-Lutetian boundary, some 48 million years ago. F. panarium is known from fossils found in the Green River Formation of Wyoming. The taxonomical relations of F. panarium remain unclear. It is sometimes placed in a distinct familyForatidae. It may or may not be related to the Cuculiformes and is sometimes seen as a "missing link" between the cuckoos and/or turacos and the puzzling hoatzin of the Amazon. The latter might be related to any number of different modern birds however; its affinities constitute a major ornithological enigma. In addition, the Eocene genus Hoatzi from Argentina has been allied to both the hoatzin and Foro and even been considered congeneric with the latter. What is certain is that the Cuculiformes, especially the turacos, are among the likelier candidates for the hoatzin's closest living relatives. There is an ancestral hoatzin, Hoazinoides, from the Early or Middle Miocene of Colombia, which would at least not contradict the assumption that Foro panarium was an ancient member of the hoatzin lineage or its predecessor. On the other hand, it has been proposed that the hoatzin belongs to a highly distinct clade of Cretaceous origin, the Metaves. As nothing certain about the evolutionary history of the hoatzin lineage throughout the Paleogene is known at all, F. panariumcannot support or contradict this hypothesis either. What can be said is that Foro, with its stocky body and rather weak flight apparatus was in all likelihood a bird that did not fly vast distances. Consequently, it is not very likely that it is congeneric with Hoatzi, as North and South America were still separate by some of shallow seas and the Central Americanisland arc when these birds lived, and seem to have shared only strong-flying and highly migratory genera such as seabirds. Being able to fly at all would still enable even a rather sedentary bird lineage to spread across all of the Americas by then of course; Foro and Hoatzi seem to be distinct genera, but nonetheless in some way related and possibly quite closely so. The phylogenetic analysis conducted by Field & Hsiang indicated that Foro panarium was a stem-turaco.
