Paracrax ("near curassow") is a genus of extinct North American flightless birds, possibly related to modern seriemas and the extinct terror birds. Part of Bathornithidae (though some analysis recover it as closer to the living seriemas instead,[Mayr, G., & Noriega, J. I. A well-preserved partial skeleton of the poorly known early Miocene seriema Noriegavis santacrucensis (Aves, Cariamidae).] or possibly entirely out of Cariamiformes[Gerald Mayr (2016). "Osteology and phylogenetic affinities of the middle Eocene North American Bathornis grallator—one of the best represented, albeit least known Paleogene cariamiform birds (seriemas and allies)". Journal of Paleontology 90 (2): 357–374. doi:10.1017/jpa.2016.45.]), it is a specialised member of this group, being cursorial carnivores much like their South American cousins, some species attaining massive sizes.
Discovery
Paracrax antiqua is the genus type species.
The type specimen,
YPM 537, was collected in
Weld County,
Colorado, in 1871 by Othniel Charles Marsh, which identified it as a sort of turkey.
[Marsh 1871] It was posteriorly referred to
Cracidae by
Pierce Brodkorb,
[Brodkorb 1964] before its identity as a bathornithid came to light.
Material previously identified as a
cormorant, "
Phalacrocorax/
Oligocrocorax"
mediterraneus, was posteriorly identified as
P. antiqua remains.
Since then, two more species have been identified: P. wetmorei and P. gigantea. These were more closely related to each other than to P. antiqua.
Paleoecology
Most specimens have been found on the
Brule Formation of
North Dakota. Dating to the
Rupelian stage of the
Oligocene, it is composed of river deposits that showcase the remains of a rich
savanna-like environment. Several large sized mammal groups are known from this region, such as
rhinoceri,
and
Hyaenodonta, all co-existing with several flightless bathornithids.
Bathornis, a possible close relative of
Paracrax, appears to have favoured wetter ecosystems, while
Paracrax occurs in drier environments.
Appearance
Paracrax is known from a variety of materials, such as
, keels,
forelimb elements and coracoids. The
humerus material is distinct from the closely related
Bathornis by an internal
condyle that is less distinctively raised in relation to the external condyle. Overall, it can be assumed that it had similar proportions to
, with proportionally short wings and a large, deep bill.
The keel is rather proportionally , like a ratite's. It has unique characteristics quite unlike the of any other bird (though vaguely convergent to that of the modern hoatzin), making it easily identifiable.[Joel Cracraft, Systematics and evolution of the Gruiformes (Class Aves). 2, Additional comments on the Bathornithidae, with descriptions of new species. American Museum Novitates; no. 2449]
Paracrax gigantea in particular is a very large bird, reaching estimated heights of over , making it among the largest of bathornithids and among the tallest animals in its environment.
Lifestyle
Like most Cariamiformes, including other bathornithids,
Paracrax was likely a terrestrial carnivore. In terms of ecology, it would probably have been similar to its more famous relatives, the
phorusrhacid terror birds, being a large, flightless killer and using its large
axe-like
beak to subdue and kill its prey. It is a prime example of a large flightless predatory bird co-existing with large predatory mammals, such as the conspecific
Hyaenodon,
Dinictis, and
Archaeotherium with which it probably shared an apex-predator role in its environment.
