Tetraoninae (grouse) and Meleagridinae (turkeys) are conspicuous representatives of the modern North American avifauna. The pre-Pleistocene fossil record of these clades has historically been limited to fragmentary remains, in some cases contributing to confusion rather than improving our understanding of how these charismatic landfowl evolved. We report an exquisitely preserved partial skeleton representing a new species of Late Miocene phasianid from the Ash Hollow Formation of Nebraska. Centuriavis lioae is a phasianid species close in size to modern sage-grouse that diverged prior to the grouse-turkey split and thus offers insight into the early history of this radiation. The cranial endocast resembles other North American phasianids and differs from odontophorids in exhibiting a strongly projected Wulst bordered by a well-defined vallecula. Phylogenetic analyses indicate that Centuriavis lioae gen. et sp. nov. forms a clade with Tetraoninae, Meleagridinae, and Pucrasia macrolopha (Koklass pheasant). The new fossil species provides a late Miocene minimum calibration for the divergence of these extant taxa from other Galliformes and supports the hypothesis of a single dispersal from Asia to North America by a lineage that later gave rise to grouse and turkeys.

In order to resolve the phylogenetic placement of Centuriavis lioae, we scored the new taxon into the morphological data matrix of Ksepka (2009). We added 16 new characters and two additional fossil taxa, the possible stem phasianid Palaeortyx gallica and the recently described crown phasianid Panraogallus hezhengensis. The expanded matrix contains 136 characters based on osteology, soft tissue anatomy, and reproductive biology and samples seven outgroup species (Lithornithiformes, Tinamiformes, and Anseriformes), 55 extant species of Galliformes, and five fossil species of Galliformes. 

In order to constrain the relationships of extant taxa, we applied a backbone constraint topology based on the results of a recent ML analysis of 2,208,355 bp of molecular sequence data from 4,817 concatenated UCE loci by Hosner et al. (2017). This backbone is included as a tree in the NEXUS file.