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| Navaornis hestiae Chiappe, Navalón, Martinelli, Carvalho, Santucci, Wu & Field, 2024 |
Abstract
A dearth of Mesozoic-aged, three-dimensional fossils hinders understanding of the origin of the distinctive skull and brain of modern (crown) birds. Here we report Navaornis hestiae gen. et sp. nov., an exquisitely preserved fossil species from the Late Cretaceous of Brazil. The skull of Navaornis is toothless and large-eyed, with a vaulted cranium closely resembling the condition in crown birds; however, phylogenetic analyses recover Navaornis in Enantiornithes, a highly diverse clade of Mesozoic stem birds. Despite an overall geometry quantitatively indistinguishable from crown birds, the skull of Navaornis retains numerous plesiomorphies including a maxilla-dominated rostrum, an akinetic palate, a diapsid temporal configuration, a small cerebellum and a weakly expanded telencephalon. These archaic neurocranial traits are combined with a crown bird-like degree of brain flexion and a bony labyrinth comparable in shape to those of many crown birds but substantially larger. Altogether, the emergent cranial geometry of Navaornis shows an unprecedented degree of similarity between crown birds and enantiornithines, groups last sharing a common ancestor more than 130 million years ago. Navaornis provides long-sought insight into the detailed cranial and endocranial morphology of stem birds phylogenetically crownward of Archaeopteryx, clarifying the pattern and timing by which the distinctive neuroanatomy of living birds was assembled.
Systematic palaeontology
Aves Linnaeus, 1758
Ornithothoraces Chiappe and Calvo, 1994
Enantiornithes Walker, 1981
Navaornis hestiae gen. et sp. nov.
Remarks. We use Aves to refer to all taxa descended from the most recent common ancestor of Archaeopteryx lithographica and crown birds.
Diagnosis. Enantiornithine with a toothless skull and a combination of the following features: fully fused premaxillae with a convex dorsorostral surface, highly curved jugal, small, comma-shaped quadratojugal, diminutive lacrimal failing to separate the orbit from the antorbital fenestra, parasphenoidal rostrum perforated by a large ovoid fenestra, elongate basipterygoid processes, large and sinusoidal anterior semicircular canal excavating the dorsal margin of the supraoccipital, robust and prominent medial process of the mandible.
Etymology. Navaornis honours William Nava, who discovered the fossil locality in 2004 and the holotype specimen in 2016; the specific epithet hestiae alludes to Hestia, the Greek goddess of architecture, regarded as simultaneously the oldest and the youngest of the Twelve Olympians. Navaornis reflects this duality in that it belongs to an archaic lineage, yet its cranial geometry is essentially modern.
Luis M. Chiappe, Guillermo Navalón, Agustín G. Martinelli, Ismar de Souza Carvalho, Rodrigo Miloni Santucci, Yun-Hsin Wu and Daniel J. Field. 2024. Cretaceous Bird from Brazil informs the Evolution of the Avian Skull and Brain. Nature. 635, 376–381. DOI: doi.org/10.1038/s41586-024-08114-4
