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| Asteriornis maastrichtensis
Field, Benito, Chen, Jagt & Ksepka, 2020
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Abstract
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 period, 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 ecology, biogeography and divergence times 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 birds. 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 era, 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 locality 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 birds, and its relatively small size and possible littoral ecology may corroborate proposed ecological filters that influenced the persistence of crown birds through the end-Cretaceous mass extinction.
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| Digitally segmented skull of Asteriornis maastrichtensis. |
Systematic palaeontology
Avialae Gauthier, 1986
Neornithes Gadow, 1892
Neognathae Pycraft, 1900
Pangalloanserae Gauthier and de Queiroz, 2001
Asteriornis maastrichtensis gen. et sp. nov.
Remarks. We use Avialae to refer to theropods crownward of Dromaeosauridae and Troodontidae. Neornithes is equivalent to the bird crown group (Aves sensu Gauthier, 198623). Pangalloanserae defines the most inclusive clade including Anser anser and Gallus gallus but not Passer domesticus (that is, the galloanseran total group). Further phylogenetic definitions are presented in the Supplementary Information.
Etymology. Asteriornis, from the name of the Titan goddess Asteria and the Greek ornis for bird. In Greek mythology Asteria is the goddess of falling stars and transforms herself into a quail—attributes that are reflected by both the impending Cretaceous–Palaeogene (K–Pg) asteroid impact and the galloanseran affinities of Asteriornis. The specific epithet maastrichtensis reflects the provenance of the holotype—the Maastricht Formation (the type locality of the Late Cretaceous Maastrichtian stage).
Holotype. Natuurhistorisch Museum Maastricht (NHMM) 2013 008, a nearly complete, articulated skull including mandibles and associated postcranial remains preserved in four blocks (Fig. 1, Extended Data Figs. 1–7; see Supplementary Information for videos, character information, measurements, additional description and discussion). Preserved elements include the premaxillae, maxillae, nasals, frontals, laterosphenoid, basisphenoid, mesethmoid, left quadrate, left jugal, right palatine and lower jaws. Associated postcranial elements include incomplete femora, tibiotarsi, tarsometatarsus and radius.
Locality and age. CBR-Romontbos Quarry, Eben-Emael, Liège, Belgium. Valkenburg Member (66.8–66.7 million years old), Maastricht Formation, Late Maastrichtian, Cretaceous. Additional details regarding the locality and stratigraphic setting are presented in the Supplementary Information.
Diagnosis. Asteriornis is unique among known taxa in exhibiting caudally pointed nasals that overlie the frontals and meet at the midline of the skull, and a slightly rounded, unhooked tip of the premaxilla. Additional character combinations from phylogenetic analyses that differentiate Asteriornis are presented in the Supplementary Information.
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| An artist’s reconstruction of the world’s oldest modern bird, Asteriornis maastrichtensis, in its original environment. Parts of Belgium were covered by a shallow sea 66.7 million years ago, and conditions were similar to modern tropical beaches like the Bahamas. Asteriornis had fairly long legs and may have prowled the prehistoric shoreline. |
Daniel J. Field, Juan Benito, Albert Chen, John W. M. Jagt and Daniel T. Ksepka. 2020. Late Cretaceous Neornithine from Europe illuminates the Origins of Crown Birds. Nature. 579; 397–401. DOI: 10.1038/s41586-020-2096-0
