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Coelurosauria
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- For the prehistoric gliding reptile, see Coelurosauravus.
Coelurosauria is the clade containing all theropod dinosaurs more closely related to birds than to carnosaurs. It is a diverse group that includes tyrannosaurs, ornithomimosaurs, and maniraptors; Maniraptora includes birds, the only descendents of coelurosaurs alive today. All feathered dinosaurs discovered so far have been coelurosaurs; some scientists believe that most members of coelurosauria bore some kind of feathers.
coelurosaurs were bipedal predators.
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Encyclopedia
- For the prehistoric gliding reptile, see Coelurosauravus.
Coelurosauria is the clade containing all theropod dinosaurs more closely related to birds than to carnosaurs. It is a diverse group that includes tyrannosaurs, ornithomimosaurs, and maniraptors; Maniraptora includes birds, the only descendents of coelurosaurs alive today. All feathered dinosaurs discovered so far have been coelurosaurs; some scientists believe that most members of coelurosauria bore some kind of feathers.
Description
Most coelurosaurs were bipedal predators. The group includes some of the largest (Tyrannosaurus) and smallest (Microraptor, Parvicursor) carnivorous dinosaurs ever discovered. Characteristics that distinguish coelurosaurs include:
- a sacrum (series of vertebrae that attach to the hips) longer than in other dinosaurs
- a tail stiffened towards the tip
- a bowed ulna (lower arm bone).
- a tibia (lower leg bone) that is longer than the femur (upper leg bone)
Feathers: a possible coelurosaurian trait
To date, fossilized traces of feathers have been identified only among coelurosauria. Feathers of some type, or morphological features suggesting feathers, have been found in fossils of at least one species in all coelurosaur subgroups other than ornithomimosauria. Modern birds are classified as coelurosaurs by nearly all palaeontologists. The arrangements of feathers currently observed on coelurosauria other than the aves are without exception more primitive, despite being of a later date, and some coelurosauria species are known to have bare skin rather than feathers.
Fossil evidence and age
A few fossils tentatively associated with the coelurosauria date back as far as the late Triassic . What has been found between then and the start of the late Jurassic is fragmentary. A typical example is Iliosuchus, known only from two ilia bones in the mid Jurassic. It was a 1.5 m long carnivore from about 165 Ma (million years ago) in Oxfordshire and is tentatively assigned to the Tyrannosauroidea.
Many nearly complete fossil coelurosaurians are known from the late Jurassic. Archaeopteryx (incl. Wellnhoferia) is known from Bavaria at 155-150 Ma. Ornitholestes, the troodontid WDC DML 110, Coelurus fragilis and Tanycolagreus topwilsoni are all known from the Morrison Formation in Wyoming at about 150 Ma. 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 Ma.
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. Almost all the theropod dinosaurs from the Yixian Formation are coelurosaurians. Many of the coelurosaurian lineages survived up 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.
Classification
The phylogeny and taxonomy of Coelurosauria has been subject to intensive research and revision. For many years, coelurosauria was a 'dumping ground' for all small theropods. 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 discovered that many small theropods were not 'coelurosaurs' at all and that some large theropods, such as the tyrannosaurids, were actually giant coelurosaurs. Even more drastically, the segnosaurs, once not even regarded as theropods, have turned out to be non-carnivorous coelurosaurs related to Therizinosaurus. Senter (2007) listed 59 different published phylogenies since 1984. Those since 2005 have followed almost the same pattern, and differ significantly from many older phylogenies.
The following phylogenetic results are taken from Senter (2007) "A new look at the Phylogeny of Coelurosauria (Dinosauria: Theropoda)." This cladogram does not represent time, but a crude estimate of the time can be inferred from morphological changes. The first coelurosaurs were similar to the coelurids Tanycolagreus and Coelurus, and differed only sightly from other early tyrannosauroids Dilong and Eotyrannus. The two most significant separations between subgroups are those between the Paraves and other coelurosaurs and between the paravian clades Avialae and Deinonychosauria.
1 Coelurosauria, 2 Tyrannosauroidea, 3 Coeluridae, 4 Compsognathidae, 5 Maniraptoriformes, 6 Ornithomimosauria, 7 Maniraptora, 8 Therizinosauroidea, 9 Therizinosauridae, 10 Alvarezsauridae, 11 Oviraptorosauria, 12 Oviraptoridae, 13 Ingeniinae, 14 Paraves, 15 Avialae, 16 Aves, 17 Ornithurae, 18 Deinonychosauria, 19 Troodontidae, 20 Dromaeosauridae, 21 Unenlagiinae, 22 Microraptoria, 23 Dromaeosaurinae
"Coelurosaurus"
"Coelurosaurus" is an informal generic name, attributed to Friedrich von Huene, 1929, that is sometimes seen in lists of dinosaurs. The name is undescribed and has not been used seriously, although it has appeared in works of fiction.
See also
Feathered dinosaurs
Origin of birds
List of fossil birds
External links
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