Bathornis

Classification

Bathornis is the type genus of Bathornithidae, a family of Cariamiformes related to modern seriemas and extinct forms such as phorusrhacids, Strigogyps and idiornithids. Interspecific relations within Cariamiformes are unresolved; bathornithids have been considered sister to seriemas, phorusrhacids or idiornithids, and sometimes a polyphyletic group.

Bathornis is usually considered the sister clade to Paracrax, with Neocathartes and other taxa possibly nested within it. One phylogenetic study recovered Bathornis as closer to phorusrhacids than to Paracrax, but this is considered premature. A recent study placed Bathornis as the sole bathornithid, outside the seriema-phorusrhacid clade, while a 2024 study found it closer to seriemas than phorusrhacids.

Species

Bathornis is the most speciose of all Cariamiformes, with at least five consistently recognised species. The type species, B. veredus, is known from Eocene and Oligocene deposits of the Chadron Formation in Colorado and Nebraska, from multiple tibiotarsal material depicting an animal roughly the size of a modern emu. Skull material is also known. B. cursor, described by Alexander Wetmore in 1933, occurs in the same deposits as B. veredus and is similar in size but distinct in trochlea features; it occurs in considerably earlier deposits.

B. geographicus, described by Wetmore in 1942, is an upper Oligocene species from South Dakota, Nebraska and Wyoming, possibly a direct descendant of B. veredus. It is larger than B. veredus and B. cursor, quite possibly the largest described member of the genus, and co-existed with Paracrax gigantea in the Brule Formation. Another species, originally referred to the rallid genus Palaeocrex, was later shown to belong to Bathornis; it may represent a different species or a younger morph of B. veredus, and if distinct is among the smallest forms, about the size of a modern seriema.

Palaeobiology

Bathornis species were large, terrestrial birds with long and powerful legs. Most if not all were flightless, perhaps more specialised to this regard than Paracrax, with proportionally short wings and keel and a reduced processus acrocoracoideus in the coracoid. It was carnivorous, with a strong beak akin to that of phorusrhacids, sharing an identical reinforcement of the jugal. Larger species were likely apex predators within their environment, competing successfully with mammals for over 17 million years.

Palaeoecology

Bathornis lived across a variety of habitats, mostly in what is now the Great Plains. Early researchers pictured it striding over open plains, but newer studies suggest it likely preferred wetlands.

The species B. cursor is often found alongside Megacerops, and B. geographicus with Merycoidodon, hinting that Bathornis may have preyed on these mammals. It shared its world with predators like hyaenodontids, entelodonts, and nimravids, plus the related bird Paracrax. Competition with Paracrax is likely, and there are signs of niche partitioning, since Paracrax is found in drier areas.

Did You Know?

• The type specimen of Bathornis veredus was recovered by Philip Reinheinter from Oligocene deposits that also yielded the cathartid Phasmagyps.
• Two birds described alongside B. veredus—the putative rallid Palaeocrex and the putative cathartid Palaeogyps—later turned out to be bathornithid material.
• The species name 'veredus' is a Latin word relating to speed.