SupplementaryData2.txt

Researchers described the first crown bird from the Late Cretaceous (Maastrichtian) Hell Creek Formation. They identified a well-preserved synsacrum, with traits linking it to Neornithes. Phylogenetic study places it as a presbyornithid, an extinct anseriform group previously hinted at but not confirmed in the Hell Creek Formation. This study provides new insights into the origins, radiation, and paleoecology of early neornithines before the K-Pg mass extinction event.