Our understanding of the earliest stages of crown bird evolution is hindered by an exceedingly sparse avian fossil record from the Mesozoic era. The most ancient phylogenetic divergences among crown birds are known to have occurred in the Cretaceous period1,2,3, but stem-lineage representatives of the deepest subclades of crown birds—Palaeognathae (ostriches and kin), Galloanserae (landfowl and waterfowl) and Neoaves (all other extant birds)—are unknown from the Mesozoic era. As a result, key questions related to the ecology4,5, biogeography3,6,7 and divergence times1,8,9,10 of ancestral crown birds remain unanswered. Here we report a new Mesozoic fossil that occupies a position close to the last common ancestor of Galloanserae and fills a key phylogenetic gap in the early evolutionary history of crown birds10,11. Asteriornis maastrichtensis, gen. et sp. nov., from the Maastrichtian age of Belgium (66.8–66.7 million years ago), is represented by a nearly complete, three-dimensionally preserved skull and associated postcranial elements. The fossil represents one of the only well-supported crown birds from the Mesozoic era12, and is the first Mesozoic crown bird with well-represented cranial remains. Asteriornis maastrichtensis exhibits a previously undocumented combination of galliform (landfowl)-like and anseriform (waterfowl)-like features, and its presence alongside a previously reported Ichthyornis-like taxon from the same locality13 provides direct evidence of the co-occurrence of crown birds and avialan stem birds. Its occurrence in the Northern Hemisphere challenges biogeographical hypotheses of a Gondwanan origin of crown birds3, and its relatively small size and possible littoral ecology may corroborate proposed ecological filters4,5,9 that influenced the persistence of crown birds through the end-Cretaceous mass extinction.
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The holotype specimen of A. maastrichtensis is deposited in the permanent collection of the Natuurhistorisch Museum Maastricht under collection number NHMM 2013 008. Digital models of the A. maastrichtensis skull and postcranial elements, .tre files from phylogenetic analyses and CT scans of the A. maastrichtensis holotype are available at Zenodo (doi: 10.5281/zenodo.3610226). The Life Science Identifier for Asteriornis is urn:lsid:zoobank.org:pub:32192A46-4A43-48CE-8F17-447900FCC6DF.
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We thank M. van Dinther for collecting and donating the specimen; J. Vellekoop for advice on geochronology; K. Smithson, T. Thompson and V. Fernandez for scanning support; M. Brooke, M. Lowe, M. Clementz, L. Vietti, J. Cooper, J. White, C. Levitt, R. Irmis, K. MacKenzie and J. Sertich for collections assistance; B. Creisler for etymological information; and T. Worthy and J. Watanabe for anatomical advice. We are grateful to L. Witmer and F. Degrange for sharing three-dimensional models of Presbyornis and Conflicto, respectively, and to P. Krzeminski for his artwork. D.J.F. acknowledges support from the UK Research and Innovation Future Leaders Fellowship MR/S032177/1, the Royal Society Research Grant RGS/R2/192390, a Systematics Association Research Grant and the Isaac Newton Trust; J.B. acknowledges the Hesse Award from the American Ornithological Society and grants from the Jurassic Foundation, Geological Association and Paleontological Society; and D.T.K. acknowledges support from the NSF award DEB 1655736.
The authors declare no competing interests.
Peer review information Nature thanks Jingmai O’Connor and Kevin Padian for their contribution to the peer review of this work.
Publisher’s note Springer Nature remains neutral with regard to jurisdictional claims in published maps and institutional affiliations.
Extended data figures and tables
The views of the cranium are similar to those in Fig. 1, but with the jaws removed to illustrate the ventral portion of the skull.
Extended Data Fig. 2 Higher-resolution cranial and mandibular anatomy of A. maastrichtensis (NHMM 2013 008).
Labels have been removed and images enlarged to show details.
Extended Data Fig. 3 Morphology of individually segmented skull elements from A. maastrichtensis (NHMM 2013 008).
Dorsal, ventral and rostral views of the frontals show the nasals separated from their in situ position to illustrate the morphology of the nasofrontal contact. Scale bars, 1 cm.
Skulls and quadrates of extant Galliformes and total-group Anseriformes. The skull of Presbyornis USNM 299846 is shown. Scale bars, 5 mm (quadrates); 1 cm (skulls). Skulls are in left lateral view except Presbyornis, which is in reflected right lateral view. FPB, foramen pneumaticum basiorbitale; FPR, foramen pneumaticum rostromediale.
Retroarticular regions of left mandibles in lateral (left), medial (middle) and dorsal (right) views. Both the left and right mandibles of Asteriornis are shown in dorsal view, as the retroarticular process is only preserved on the left mandible and the medial process is only preserved on the right mandible. Images of Anatalavis are mirrored. Scale bars, 1 cm.
The left distal femur of Presbyornis pervetus (UW 27596) is shown for comparison.
a, Block containing the left femur, left tibiotarsus and the main portion of the skull, viewed from the side with the femur exposed. b, Same block as in a, viewed from the side containing the tibiotarsus. c, Block containing the right femur and tarsometatarsus. d, Block containing the right distal radius, several unidentified bone fragments and a portion of the cranial roof near the frontoparietal suture. e, Block containing the right tibiotarsus. Numerous fragments of fossil echinoderms and molluscs are visible within the blocks. Scale bars, 1 cm.
Estimate of the mean body size of the Asteriornis holotype25 compared with extant Galloanserae82, ranked on the x axis from smallest to largest. The mean body-size estimate for Asteriornis (394 g) is closest to that of male Anas crecca (392 g; 7.8th percentile among Anseriformes) and female Perdix perdix (393 g; 33rd percentile among Galliformes).
a, Results of the parsimony analysis. Asteriornis (pink) resolves as the sister taxon to crown Galloanserae. b, Results of the tip-dated Bayesian analysis with a soft-maximum neornithine root age of 86.5 million years. An estimated timescale is shown on the x axis, although see caveats relating to divergence times in the Supplementary Information. Asteriornis (pink) resolves as the stemward-most member of Pangalliformes. Colours match those in Fig. 3 and extinct taxa are denoted with daggers. See Supplementary Information for full details of phylogenetic analyses, character information, synapomorphies of key clades, support values and tree files.
This file contains: Museum Abbreviations, Scan Parameters, Supplementary Video Descriptions, Supplementary Methods (Phylogenetic Analyses), and Supplementary Notes (Provenance Data for New Fossil Material, Phylogenetic Definitions of Clade Names, Additional Anatomical Observations, Synapomorphies Diagnosing Key Clades, Morphological Character Descriptions, Supplementary References) – see Contents page for details.
Character-taxon matrix: Nexus file used for the phylogenetic analyses.
NHMM 2013 008, Skull of Asteriornis maastrichtensis holotype, yaw video.
NHMM 2013 008, Skull of Asteriornis maastrichtensis holotype, roll video.
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Field, D.J., Benito, J., Chen, A. et al. Late Cretaceous neornithine from Europe illuminates the origins of crown birds. Nature 579, 397–401 (2020). https://doi.org/10.1038/s41586-020-2096-0