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Coelurosauria (; from Greek language, meaning "hollow-tailed lizards") is the clade containing all theropod more closely related to than to carnosaurs.
Coelurosauria is a subgroup of theropod dinosaurs that includes Compsognathidae, Tyrannosauroidea, ornithomimosaurs, , and over the recent years, (Although position within the clade is unclear). Maniraptora includes , the only known dinosaur group alive today.Turner, A.H., Makovicky, P.J., and Norell, M.A. 2012. A review of dromaeosaurid systematics and paravian phylogeny. Bulletin of the American Museum of Natural History 371: 1–206. In the past, Coelurosauria was used to refer to all small theropods, but this classification has since been amended.
Most feathered dinosaurs discovered so far have been coelurosaurs. Philip J. Currie had considered it likely and probable that all coelurosaurs were feathered. However, several skin impressions found for some members of this group show pebbly, scaly skin, indicating that feathers did not completely replace scales in all taxa.
Though once thought to be a feature exclusive to coelurosaurs, feathers or feather-like structures are also known in some dinosaurs (like Tianyulong and Kulindadromeus), and in . Though it is unknown whether these are related to true feathers, recent analysis has suggested that the feather-like integument found in ornithischians may have evolved independently of coelurosaurs but this was estimated by assuming that primitive pterosaurs had scales. In 2018, two anurognathid specimens were found to have integumentary structures similar to protofeathers. Based on phylogenetic analysis, protofeathers would have had a common origin with Avemetatarsalia.
In the early Cretaceous, a superb range of coelurosaurian fossils (including avians) are known from the Yixian Formation in Liaoning. All known theropod dinosaurs from the Yixian Formation are coelurosaurs. Many of the coelurosaurian lineages survived to the end of the Cretaceous period (about 66 Ma) and fossils of some lineages, such as the Tyrannosauroidea, are best known from the late Cretaceous. A majority of coelurosaur groups became extinct in the Cretaceous–Paleogene extinction event, including the Tyrannosauroidea, Ornithomimosauria, Oviraptorosauria, Deinonychosauria, Enantiornithes, and Hesperornithes. Only the Neornithes, otherwise known as modern birds, survived, and continued to diversify after the extinction of the other dinosaurs into the numerous forms found today.
There is consensus among paleontologists that birds are descended from coelurosaurs. Under modern cladistics definitions, birds are considered the only living lineage of coelurosaurs. Birds are classified by most paleontologists as belonging to the subgroup Maniraptora.
A portion of a tail belonging to a juvenile coelurosaur was found in 2015, inside of a piece of amber.
In 1994, a study by Paleontology Thomas Holtz found a close relationship between the Ornithomimosauria and Troodontidae, and named this group Bullatosauria. Holtz rejected this hypothesis in 1999, and most paleontologists now consider troodontids to be much more closely related to either or Dromaeosauridae than they are to ornithomimosaurs, causing the Bullatosauria to be abandoned. The name referred to the inflated (bulbous) Sphenoid bone both groups shared. Holtz defined the group as the clade containing the most recent common ancestor of Troodon and Ornithomimus and all its descendants. The concept is now considered redundant, and the clade Bullatosauria is now viewed as synonymous with Maniraptoriformes. In 2002, Gregory S. Paul named an apomorphy-based clade Avepectora, defined to include all theropods with a bird-like arrangement of the pectoral bones, where the angled shoulder girdle (coracoids) come in contact with the breastbone (sternum). According to Paul, ornithomimosaurs are the most basal members of this group.Paul, G.S. (2002). Dinosaurs of the Air: The Evolution and Loss of Flight in Dinosaurs and Birds. Baltimore: Johns Hopkins University Press. . In 2010, Paul used Avepectora for a smaller clade, excluding ornithomimosaurs, compsognathids and alvarezsauroids.Paul, G. S. (2010). The Princeton field guide to dinosaurs Princeton University Press. Princeton, New Jersey.
Within Coelurosauria exists a slightly less inclusive clade named Tyrannoraptora. This clade was defined by Sereno (1999) as " Tyrannosaurus, House sparrow (the house sparrow), their last common ancestor, and all of its descendants". As tyrannosauroids are considered to be the most basal large group within Coelurosauria, this means that the common ancestor of tyrannosauroids and birds was an even more basal coelurosaurian. As a result, almost all coelurosaurians are also tyrannoraptorans, with the only exceptions being particularly basal species such as Zuolong or Sciurumimus.
Several recently-named clades have been proposed to define the structure of Coelurosauria crownward of basal groups such as tyrannosauroids and compsognathids. Maniraptoromorpha, defined by Andrea Cau in 2018, includes all coelurosaurians more closely related to birds than to tyrannosauroids. Cau stated that the synapomorphies of the clade included "Keel or carinae in the postaxial cervical centra, absence of hyposphene-hypantra in caudal vertebrae (reversal to the plesiomorphic theropodan condition), a prominent dorsomedial process on the semilunate carpal, a convex ventral margin of the pubic foot, a subrectangular distal end of the tibia and a sulcus along the posterior margin of the proximal end of the fibula." Another proposed clade is Neocoelurosauria, erected by Hendrickx, Mateus, Araújo and Choiniere (2019), They define it as "the clade Compsognathidae + Maniraptoriformes", which can be more or less inclusive than Maniraptoromorpha depending on the topology.
The last, and most exclusive of these proposed subclades is Maniraptoriformes. Maniraptoriformes is a clade which may have been united by the presence of pennaceous feathers and wings. This clade contains ornithomimosaurs and . The group was named by Thomas Holtz, who defined it as "the most recent common ancestor of Ornithomimus and birds, and all descendants of that common ancestor." One of the possible synapomorphies of this clade is the presence of feathers homologous to those of birds, based on study of a specimen of Shuvuuia.
The following family tree illustrates a synthesis of the relationships of the major coelurosaurian groups based on various studies conducted in the 2010s.
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