Centuriavis

Centuriavis Temporal range:Miocene(Clarendonian)
Scientific classification
Domain:	Eukaryota
Kingdom:	Animalia
Phylum:	Chordata
Class:	Aves
Order:	Galliformes
Family:	Phasianidae
Genus:	†Centuriavis Ksepkaet al.,2022
Species
Centuriavis lioaeKsepkaet al.,2022

Centuriavisis an extinct genus ofphasianidlandfowlfrom the Miocene ofNebraska.Known from a well preserved and articulated skeleton preserving the skull as well as much of the vertebral column, its name stems from the fact that it remained undescribed for nearly a hundred years. It is estimated that it weighed 1.7 kg (3.7 lb), which would make it comparable in size with the average femalegreater sage grouse.Centuriavismay be related to grouse and turkeys and only a single species has been described:Centuriavis lioae.

History and naming

The type material ofCenturiavisconsists of an articulated fossil preserving primarily the front of the body including the skull, pectoral girdle, wings and the vertebrae up to and including parts of thesynsacrum.These remains were collected by the 1932 Skinner Expedition at theMachaerodusquarry, a locality within the Merritt Dam Member of theAsh Hollow Formation.TheMachaerodusquarry is generally thought to beClarendonianin age, with the overlying ash layer indicating a minimum age of 11.4 million years. The same locality also yielded an additionalhumerusabout 88% the size of theholotypeand atarsometatarsus,both of which have been tentatively referred toCenturiavisby Ksepka and colleagues. They note that the size difference could potentially be explained by sexual dimorphism, with the type specimen belonging to a male while the referred humerus may have been that of a female. However, they also note that the material could also have belonged to a different, second type of galliform. Despite the relative completeness and preservation of the type specimen, the fossils ofCenturiavisremained undescribed for nearly a century until being examined by Ksepka and colleagues.

The massive time gap between the discovery and description of the bird is also the basis for the genus' scientific name, consisting of "centuria" (one hundred) and "avis" (bird). The species name derives from Suzanne Lio, managing director at theBruce Museum of Arts and Sciencewhere the fossil was previously held.

Description

The beak ofCenturiavisis proportionally shorter than in modern turkeys with a tip that's slightly downturned. The nares are small, resembling those ofptarmigansandprairie chickens.The skull roof is smooth, which differs from grouses and some individuals of the turkey which possess rugosities above the eyes. The lower jaw is more strongly curved than in turkeys with a short mandibular symphysis that lacks a fenestra. The preservation of the skull allowed for a detailed look at the neuroanatomy ofCenturiavis,revealing that it possessed smallolfactory bulbs,a trait typical for land fowl. Thehyperpallium,also known as wulst, most closely resembles turkeys in its degree of projection. The well developedoptic lobeslikewise resemble turkeys and are located almost entirely behind the widest point of the endocast.

As prior research has shown that the strongest indicator for body mass in landfowls was the length of thecoracoid,Ksepka and colleagues were able to estimate the weight ofCenturiavis.They concluded that the animal may have reached a bodymass of 1.718 kg (3.79 lb), which is close to the average weight reported in femalegreater sage-grouse.This would renderCenturiavislarger than most extant grouse species, but still smaller than the largest modern grouse species (such as thewestern capercaillie) and modern turkeys.

Phylogeny

Two primary analysis were conducted to determine the position ofCenturiaviswithin galliforms, both using the molecular backbone constraint established by Hosner and colleagues in 2017.Of these two phylogenetic analysis, the first recoveredCenturiavisin a large polytomy within crown phasianids alongsideturkeys,grouse,true partridgesand variouspheasants.The reason for this poorly resolved result is the inclusion ofPanraogallus,a genus that is equally plausible to be a stem-turkey, stem-grouse or some other type of phasianid. Removing this taxon from the analysis yielded a better resolved phylogenetic tree, excluding many pheasants from the polytomy present in the prior analysis, only leavingCenturiavis,the modernKoklass pheasant,turkeys and grouse. However there is little support for this clade given the material lacking inCenturiavisand the major skeletal differences between grouse and turkeys, with only a singlesynapomorphyrecovered.

Arborophilinae(wood and jungle partridges) Blood pheasant Pavovinae(peafowl and peacock pheasant) Coturnicinae(quails and allies) Long-billed partridge Red junglefowl Chinese bamboo partridge Black francolin Satyr tragopan Himalayan monal Grey partridge Reeves's pheasant Lady Amherst's pheasant Common pheasant Cheer pheasant White eared pheasant Bulwer's pheasant Koklass pheasant Centuriavis lioae Tetraoninae(grouse) Meleagridinae(turkeys)

Evolution of grouse and turkeys

While the relationship betweenCenturiavisand the genusPucrasiacould not be resolved, Ksepka and colleagues favor the hypothesis thatCenturiaviswas the sister taxon to the clade uniting grouse and turkeys, which would match the idea that the common ancestor of these two families dispersed from Asia into North America and only then diverged from one another. However, other factors make it unlikely that it was the direct ancestor of this clade. Prior attempts to determine the divergence date between grouse and turkeys indicate that the two lineages split from one another during the early Miocene, beforeCenturiavisappeared as part of theMachaerodusquarry fauna. To complicate matters further, said analysis were solely based on extant species, neglecting the fossil record of grouse from the Pliocene and Pleistocene of Eurasia. These remains, although fragmentary, have commonly been assigned to the various grouse genera still alive today and give some credibility to the idea that the grouse-turkey clade didn't originate in America but in Eurasia. Whichever the case, this suggests thatCenturiaviswas not the direct ancestor to turkeys and grouse, but rather an early diverging relative that would go on to coexist with its more derived relatives.