A new species of Morsoravidae sheds light on beak and limb morphology in stem passerines

Morsoravidae is a small clade of probable stem passerines known from the Eocene of Europe and North America. Here, we report an articulated skeleton of a new species of Morsoravidae from the Green River Formation of Wyoming. In contrast to <i>Morsoravis sedilis</i> and <i>Pumiliornis tessellatus</i>, in which the nares appear to have been schizorhinal, the nares of the <i>Consoravis turdirostris</i> gen. et sp. nov. are ovoid and do not extend caudally beyond the nasofrontal hinge. In addition, the processus retroarticularis is much shorter in <i>Consoravis</i> than in <i>Morsoravis</i>. The humerus is similar to that of extant passerines, with a short shaft, short crista deltopectoralis, well-developed tuberculum supracondylare dorsale, and strongly projected processus flexorius. However, the more distal wing elements differ from those of crown passerines in that the olecranon is blunt and the carpometacarpus has a weakly developed processus extensorius. Although fully zygodactyl stem passerines are now well-documented, <i>Consoravis</i> and <i>Sororavis</i> exhibit a semi-zygodactyl foot, in which the trochlea of the fourth metatarsal bears a wing-like flange but lacks a fully developed trochlea accessoria. The unspecialized beak, modest wing length, and relatively short leg together suggest arboreal habits and a generalized diet of invertebrates and fruit for <i>Consoravis</i>, in contrast to more specialized diets of the nectivorous <i>Pumiliornis</i> and the rhynchokinetic, possibly probe-feeding <i>Morsoravis</i>. Phylogenetic analyses support the monophyly of Morsoravidae and weakly support the placement of this clade as sister to all other passerines. These analyses also support the identification of the Oligocene <i>Jamna szybiaki</i> as a stem passerine and the paraphyly of Zygodactylidae.