| Asteriornis | |
|---|---|
 | |
| Skull in lateral view | |
Scientific classification | |
| Domain: | Eukaryota |
| Kingdom: | Animalia |
| Phylum: | Chordata |
| Class: | Aves |
| Infraclass: | Neognathae |
| Clade: | Pangalloanserae |
| Genus: | †Asteriornis Fieldet al.2020 |
| Type species | |
| †Asteriornis maastrichtensis Fieldet al. 2020 | |
Asteriornis ("Asteria's bird"[1]) is an extinctgenus ofbird from theLate Cretaceous ofBelgium which is known from a singlespecies,Asteriornis maastrichtensis. It was closely related to birds of the extant superorderGalloanserae 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 asIchthyornis. Asteriornis is one of the oldest-known birds irrefutably belonging to the groupNeornithes, which encompasses all modern birds. It possesses characteristics of bothgalliformes (chicken-like birds) andanseriformes (duck-like birds), indicating its position as a close relative of thelast common ancestor for both groups.[1][3]
Asteriornis may shed light on why Neornithes were the onlydinosaurs to survive theCretaceous–Paleogene extinction event. Its coexistence with non-neornithean birds such asIchthyornis 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 biogeographicancestral reconstructions usingphylogenies[8] and the discovery ofVegavis (a possible neornithean from Antarctica),[9] butAsteriornis's presence in Europe suggests that modern birds may have been widespread in northern continents in their early evolution.[1]
Asteriornis is based on specimen NHMM 2013 008, held in theMaastricht Natural History Museum (Dutch:Natuurhistorisch Museum Maastricht), which consists of an almost complete skull and fragments of leg bones and aradius. It was retrieved from four blocks of sediment found at the CBR-Romontbos quarry nearEben-Emael in theMaastricht Formation ofBelgium,[1] and was first unearthed in 2000,[10] by amateur paleontologist Maarten van Dinther,[11] who donated it to the museum.[1] This geological formation is the namesake of theMaastrichtian stage, which was the last stage of theCretaceous period and theMesozoic era. It is dated to around 66.8 to 66.7 million years old,[12] less than a million years before the arrival of the asteroid that caused theCretaceous–Paleogene extinction event, killed off all non-avian dinosaurs (and many other animals), and began theCenozoic era.[1]
The genus name,Asteriornis, was constructed fromornis, theGreek word for bird,[13] and fromAsteria, aGreek goddess who was associated with falling stars, and about whom there is a famous myth in which she transforms herself into aquail. TheAsteri part of genus name thus alludes to theChicxulub impactor (a "falling star"), and also alludes to quails which are members of the galloanserans. The species nameA. maastrichtensis is named after theMaastricht Formation.[1] The researchers who discovered and described thefossil gaveAsteriornis the nickname "Wonderchicken", which was picked up by various news outlets.[10][14]
The beak was slightly downcurved and lightweight. Unlike galloanserans, the beak did not have any specialized connections to the rest of the skull, nor a hooked tip. Instead its front tip was slightly rounded. The skull was narrowest over theorbits (eye sockets), where thefrontal bones were incised by a V-shaped part of thenasal bones. The bones forming the jaw joint were very galloanseran-like. Thequadrate bone (the cranium's contribution to the jaw joint) connected to theskull roof via two pronounced knobs, which were adjacent to a third smaller knob, the tuberculum subcapitulare. Themandible (lower jaw) connected to the quadrate with a pair of sockets, and the rear end of the lower jaw had a large hooked rearward-facing retroarticular process as well as a smaller inward-facing medial process. All of these characteristics are considered unique to (or at least most common in) galloanserans.[1]
In some respects the skull seems more similar to galliform birds such as chickens and pheasants. These include unfused snout bones and nasal bones which fork in front of the eyes. In other respects it resembles anseriform birds such as ducks and geese. Such features include the hooked retroarticular process of the jaw and apostorbital process (the portion of bone forming the rear edge of the eye socket) which curves forward at its lower extent. These demonstrate a principle of evolution that animals close to the common ancestor of two groups share some similarities with each group.[1]
Theradius fragment flattens and widens towards the wrist, where it possesses a large hooked bump. Leg bones are elongated and slender, similar in proportions and structure to modern ground-living birds. Thefemur has well-developed muscle ridges and a large, angularmedial condyle. Thetibiotarsus is widest towards the knee, while thetarsometatarsus is thinner and covered with ridges.[1]
Aphylogenetic analysis placedAsteriornis near the base ofGalloanserae, an expansive superorder containing birds such as chickens, ducks, pheasants, and other types of fowl and gamebirds. The precise placement varied based on whether the analysis usedparsimony orBayesian protocol. Parsimony placed it as thesister taxon to Galloanserae, meaning that it was a distant relative of thelast common ancestor of chickens and ducks. Bayesian protocol instead placed it within Galloanserae, specifically as the sister taxon toGalliformes. This means that it was more closely related to chickens than to ducks, but also that was not a direct ancestor of modern chicken-like birds.[1]
ClassifyingAsteriornis as a relative of chickens and ducks means that it is unequivocally aneornithean. This is important because Neornithes originated at the last common ancestor of all living birds, and corresponds to the term "bird" as it refers to modern-day animals. Pre-neornithean birds such asIchthyornis,enantiornitheans, orArchaeopteryx generally resemble modern birds but retain primitive features such as teeth or wing claws.[3] Neornithean fossils are extremely rare from the Mesozoic age, and are generally fragmentary or poorly described. One of the oldest known neognath, specifically a stem-anseriform, is thepresbyornithidTeviornis from theNemegt Formation ofMongolia around70 million years ago.[15] The taxonomic identity ofVegavis from the Late Cretaceous (~69.2–68.4 Ma) ofAntarctica was debated among paleontologists until a nearly complete skull was described in 2025, which confirmed its identity as a crown group anseriform.[16]Asteriornis is based on diagnostic and well-preserved skull material and its status is less unstable, so it can be considered among the oldest known undisputed fossil of a modern-style neornithean bird.[1]
At least two studies in 2021 and 2024 recoveredAsteriornis as apaleognath, sister toLithornithidae andTinamidae, albeit "with limited support".[17][18] Other researchers still supportAsterornis as a neornithean closely related to or within Galloanserae based on morphometric and phylogenetic analyses.[19][20] A cladistic analysis from a 2024 in-press article placedAsteriornis within the crown-group Galloanserae, specifically as astem-galliform, though reexaminations of its mandible suggested that it lacked a key galloanserine feature.[21] In 2025, one phylogenetic analysis recoveredAsteriornis either within Neognathae or as a sister taxon of Palaeognathae, while the other analysis recovered it as a sister taxon ofGalliformes.[16]
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