Bathornis ("tall bird") is an extinct lineage of birds related to modern day seriemas, that lived in North America about 37–20 million years ago. Like the closely related and also extinct phorusrhacids, it was a flightless predator, occupying predatory niches in environments classically considered to be dominated by mammals. It was a highly diverse and successful genus, spanning a large number of species that occurred from the Priabonian Eocene to the Burdigalian Miocene epochs.
Description
Though most material is highly incomplete, Bathornis is nonetheless known from a variety of skeletal elements: hindlimbs (most commonly tarso-metatarsals), forelimb elements (especially humeri), pelvises and skulls. Bathornis grallator is known from a mostly complete skeleton, including the skull, bearing a proportionally large, hooked beak. The bathornithid second toe is currently unknown, but the first toe is highly reduced, as with most Cariamiformes, and like phorusrhacids it possesses a robust jugal and reduced processus acrocoracoideus of coracoid, two features possibly having evolved in convergence due to their similar lifestyle.
Overall, Bathornis is a long legged, short-winged, large skulled bird, similar in shape to phorusrhacids. Its numerous species span a large diversity of body sizes, ranging from forms about as large as modern seriemas to 2 meter tall animals.
Classification
Bathornis is the type genus of Bathornithidae, a family of Cariamiformes, related to the modern seriemas (this relationship has been recognised ever since its first description) and also a variety of extinct forms like phorusrhacids, Strigogyps and idiornithids, in turn part of the Australaves assemblage that also includes falcons, passerines and parrots. Interspecific relations within the Cariamiformes are highly volatile and unresolved, bathornithids at times having been listed as sister taxa to seriemas, phorusrhacids and idiornithids, sometimes even as a polyphyletic group.
It is usually considered the sister clade to Paracrax, and several authorities consider Neocathartes and several other taxa to be nested with it (see below). However, at least one phylogenetic study recovers Bathornis (and its synonyms) as more closely related to phorusrhacids than to Paracrax, though this is considered premature and based on far too few synapomorphies.
The most recent phylogenetic studies find Bathornis to be the sole representative of Bathornithidae, within Cariamiformes but outside of the clade composing seriemas and phorusrhacids. Paracrax is found to be outside of Bathornithidae, with its status as a Cariamiformes uncertain.
Discovery and naming
The type species is B. veredus, its type specimen being Denver Mus. Nat. Hist. No. 805, a limb element (distal portion of a metatarsus), recovered by Philip Reinheinter from Oligocene deposits of Weld County, Colorado, which also heralded the cathartid Phasmagyps. First described by Alexander Wetmore, the bird was referred as a "cedicnemidid" (a wastebasket taxon for "thick-knee" birds) related to modern seriemas, erecting the subfamily Bathornithinae. Two birds described alongside it, the putative rallid Palaeocrex and the putative cathartid Palaeogyps, would later turn out to be bathornithid material, the latter in particular synonymous with B. veredus.
The bird was noted as being massive in comparison to its modern seriema relatives, presumably the reason as to receive its genus name, "tall bird". The species name, "veredus", is not given an explanation, though it is a Latin word relating to speed.
Species
Bathornis is noted for its high number of species, and is the most speciose of all Cariamiformes, extinct or extant. A minimum of five species are consistently recognised, with several otherwise monotypic taxa often either aligned with this genus or rendered outright synonyms of established species. Some caution has been suggested, given the possibility that some sympatric species might actually represent different sexes or morphs, though the vast temporal spanning of the genus still offers a large diversity.
Bathornis veredus
The type species, whose discovery and etymology is mentioned above. It is known from Eocene and Oligocene deposits of the Chadron Formation in Colorado and Nebraska. It is known from multiple tibiotarsal material, depicting an animal roughly the size of a modern emu, something that earned it the description of "one of the most remarkable of recent additions to our fossil avifauna." Skull material from this species is also known.