Wikipedia
Bathornithidae is an extinct family of birds from the Eocene to Miocene of North America. Part of Cariamiformes, they are closely related to the still extant seriemas and the also extinct Phorusrhacidae. They were likely similar in habits, being terrestrial, long-legged predators, some of which attained massive sizes.
It has been suggested that most, if not all, North American Paleogene cariamiforme fossils are part of this group. Storrs Olson also referred the european Elaphrocnemus to this clade, though it has since been rejected. Conversely, some analysis have instead recovered them as a polyphyletic group, with Bathornis and kin being sister taxa to phorusrhacids while Paracrax is rendered closer to modern seriemas, though this assessment is heavily debated.
The most recent consensus is that Bathornithidae is relegated exclusively to Bathornis/ Neocathartes, as a clade of Cariamiformes outside of a clade including seriemas and phorusrhacids, as well as a possible european specimen. Paracrax and Eutreptornis are understood to be an odd taxon whose cariamiform affinities are not fully resolved.