Asteriornis

Asteriornis Temporal range: Late Maastrichtian 66.8–66.7 Ma PreꞒ Ꞓ O S D C P T J K Pg N ↓
Skull in lateral view
Scientific classification
Domain:	Eukaryota
Kingdom:	Animalia
Phylum:	Chordata
Class:	Aves
Infraclass:	Neognathae
Clade:	Pangalloanserae
Genus:	†Asteriornis Field et al. 2020
Type species
†Asteriornis maastrichtensis Field et al. 2020

Asteriornis ("Asteria's bird"^[1]) is an extinct genus of bird from the Late Cretaceous of Belgium which is known from a single species, Asteriornis maastrichtensis. It was closely related to birds of the extant superorder Galloanserae such as chickens and ducks. Members of the genus were small, long-legged birds (~394 grams [13.9 oz])^[1][2] that lived near the coastline and co-existed with more "primitive" types of birds such as Ichthyornis. Asteriornis is one of the oldest-known birds irrefutably belonging to the group Neornithes, which encompasses all modern birds. It possesses characteristics of both galliformes (chicken-like birds) and anseriformes (duck-like birds), indicating its position as a close relative of the last common ancestor for both groups.^[1][3]

Asteriornis may shed light on why Neornithes were the only dinosaurs to survive the Cretaceous–Paleogene extinction event. Its coexistence with non-neornithean birds such as Ichthyornis implies that competition was not a primary factor for the extinction of non-neornitheans, which resembled modern birds in most respects but died out with other non-avian dinosaurs. Small size,^[4] a terrestrial lifestyle,^[5] and a generalist diet^[6] have all been inferred as ecological advantages possessed by early neornithes, allowing them to survive and diversify in the wake of the extinction.^[3][7] Asteriornis fulfills these qualities, suggesting that such suspicions were justified.^[1] Asteriornis is also evidence against a different hypothesis stating that modern birds originated from southern continents. This was supported by biogeographic ancestral reconstructions using phylogenies^[8] and the discovery of Vegavis (a possible neornithean from Antarctica),^[9] but Asteriornis's presence in Europe suggests that modern birds may have been widespread in northern continents in their early evolution.^[1]