Coelurosaurs Characteristics

Coelurosaurs were small, nimble land reptiles that measured 2 - 3 metres in length and that were built to survive the harsh conditions of the Triassic landscape. Unlike the cumbersome four-legged dinosaurs that were around them at that time, Coelurosaurs moved around on 2 legs (bipedal) and would travel at speed to manoeuvre themselves out of dangerous situations. Coelurosaurs had light skulls, long snouts and flexible necks which were ideal for hunting small animals such as amphibians, insects and other small reptiles. Coelurosaurs were also scavengers when food was scarce. Fossil evidence shows that all coelurosaurs were probably feathered.

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)

Modern birds are classified as coelurosaurs by nearly all palaeontologists. The arrangements of feathers currently observed on coelurosauria other than modern birds are without exception more primitive, and some coelurosaurian species are known to have had bare or scaly skin rather than feathers on at least some parts of their bodies.

Coelurosaurs were carnivorous predators that would later evolve into ferocious giants such as the Tyrannosaurus Rex and the Allosaurus. Their arrival during the Triassic period was a landmark in evolution. They quickly evolved into newer, larger species and which multiplied and spread around the Earth until by the start of the Jurassic period, dinosaurs dominated the land. Coelurosaurs were the roots of a dynasty that produced some of the most feared and largest predators ever to roam our planet.

The following are some of the major groups of Coelurosaurs:

• Coelurosauria
• Tyrannosaurids (including Tyrannosaurus Rex and Albertosaurus)
• Ornithomimidae (bird mimics, including Ornithomimus and Gallimimus)
• Maniraptora
• Dromaeosaurs - the smartest dinosaurs - the raptors, including Caudipteryx, Deinonychus, Protarchaeopteryx, Sinosauropteryx, Unenlagia, Utahraptor and Velociraptor
• Troodontids - including Troodon and Sinornithoides
• Therizinosaurs - including Therizinosaurus, Alxasaurus, Erlikosaurus, and Segnosaurus
• Oviraptors - including Oviraptor
• Aves - the birds

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 million years ago) and fossils of some lineages, such as the Tyrannosauroidea, are best known from the late Cretaceous.