Coelurosauria

Coelurosauria is the clade containing all theropod dinosaurs more closely related to birds than to carnosaurs.

Coelurosaurians Temporal range: Middle Jurassic–Present, Possible Early Jurassic record
A collection of coelurosaurian fossil skeletons: (Clockwise from upper left) GIN 100/42 which may represent Citipati or a different oviraptorosaur, Sinosauropteryx prima(a feathered compsognathid, Nothronychus mckinleyi(a therizinosaur), Tyrannosaurus rex(a large carnivorous tyrannosaur), Bambiraptor feinbergi(a small dromaeosaurid), Passer domesticus, Struthiomimus altus(an ornithomimid), Microraptor gui(a winged dromaeosaurid).
Scientific classification
Domain:	Eukaryota
Kingdom:	Animalia
Phylum:	Chordata
Clade:	Dinosauria
Clade:	Saurischia
Clade:	Theropoda
Clade:	Avetheropoda
Clade:	Coelurosauria von Huene, 1914
Subgroups
†Aniksosaurus †Bagaraatan †Bicentenaria †Lourinhanosaurus? †Phaedrolosaurus †Richardoestesia †Sciurumimus? †Teinurosaurus †Tugulusaurus †Xinjiangovenator †Zuolong? †Megaraptora? Tyrannoraptora Sereno, 1999 †Aorun †Compsognathidae (possibly polyphyletic) †Tanycolagreus †Tyrannosauroidea Maniraptoromorpha Cau, 2018 †Coelurus? †Ornitholestes Maniraptoriformes

This is a varied group that includes tyrannosaurs, ornithomimosaurs, compsognathids and maniraptors; Maniraptora includes birds, the only descendents of coelurosaurs alive today.

All Paraves discovered so far have been coelurosaurs. It is probable that all coelurosaurs were feathered.

Some diagnostic characteristics of coelurosaurs include elongated arms and well-developed hinge-like ankles (possible rotation of the ankle is reduced, which is helpful during locomotion). These features may be lost or modified by later coelurosaurs (birds, for example).

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

Fossil history

A few fossil traces of the Coelurosauria date back as far as the Upper Triassic. A possible, but not confirmed, example would be the archosaur Protoavis. What has been found between then and the start of the late Jurassic is fragmentary.

Many nearly complete fossil coelurosaurians are known from the late Jurassic. Archaeopteryx is known from Solnhofen limestone at 155-150 million years ago (mya). Ornitholestes, the troodontid WDC DML 110, Coelurus fragilis and Tanycolagreus topwilsoni are all known from the Morrison Formation in Wyoming at about 150 mya. Epidendrosaurus and Pedopenna are known from the Daohugou Beds in China, whose age is still being debated, but may be about 160 Ma or 145 mya.

The wide range of fossils in the late Jurassic and morphological evidence suggests that coelurosaurian differentiation was virtually complete before the end of the Jurassic.

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 65 Ma) and fossils of some lineages, such as the Tyrannosauroidea, are best known from the late Cretaceous. Most coelurosaur groups became extinct in the K/T extinction event. Only the Neornithes (modern birds) survived, and continued to diversify into the numerous forms found today.

There is consensus among paleontologists that birds are the descendants of coelurosaurs. Birds are classified by most paleontologists as belonging to the subgroup Maniraptora.

Related pages

• Origin of birds