Coelurosauria (/sɪˌljʊərəˈsɔːri.ə/;[3][4] from Greek, meaning "hollow-tailed lizards") is the clade containing all theropod dinosaurs more closely related to birds than to carnosaurs.

Later groups would hold on to the omnivory, while others specialized in various directions, becoming insectivorous (Alvarezsauridae), herbivorous (Therizinosauridae) and carnivorous (Tyrannosauroidea and Dromaeosauridae).

Though once thought to be a feature exclusive to coelurosaurs, feathers or feather-like structures are also known in some ornithischian dinosaurs (like Tianyulong and Kulindadromeus), and in pterosaurs.

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.

An increase in the proportion of the brain occupied by the cerebrum seems to have occurred with the advent of the Coelurosauria and "continued throughout the evolution of maniraptorans and early birds.

The oldest known unambiguous members of Coelurosauria are the proceratosaurid tyrannosauroids Proceratosaurus and Kileskus from the late Middle Jurassic.

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.

In the 1960s several distinctive lineages of coelurosaurs were recognized, and a number of new infraorders were erected, including the Ornithomimosauria, Deinonychosauria, and Oviraptorosauria.

During the 1980s and 1990s, paleontologists began to give Coelurosauria a formal definition, usually as all animals closer to birds than to Allosaurus, or equivalent specifiers.

In 1994, a study by paleontologist 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 birds or Dromaeosauridae than they are to ornithomimosaurs, causing the Bullatosauria to be abandoned.

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).

This clade was defined by Sereno (1999) as "Tyrannosaurus rex, Passer domesticus (the house sparrow), their last common ancestor, and all of its descendants".

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 tibia and a sulcus along the posterior margin of the proximal end of fibula.