oelurosaurian dinosaurs are thought to be the closest relatives of birds, in fact, birds are considered to be coelurosaurs. This is based on Gauthier's and others' cladistic analyses of the skeletal morphology of these animals. Bones are used because bones are normally the only features preserved in the fossil record. The first birds shared the following major skeletal characteristics with many coelurosaurian dinosaurs (especially those of their own clade, the Maniraptora, which includes Velociraptor):
Pubis (one of the three bones making up the vertebrate pelvis) shifted from an anterior to a more posterior orientation (see Saurischia), and bearing a small distal "boot".
Elongated arms and forelimbs and clawed manus (hands).
Large orbits (eye openings in the skull).
Flexible wrist with a semi-lunate carpal (wrist bone).
Hollow, thin-walled bones.
3-fingered opposable grasping manus (hand), 4-toed pes (foot); but supported by 3 main toes.
Reduced, posteriorly stiffened tail.
Elongated metatarsals (bones of the feet between the ankle and toes).
S-shaped curved neck.
Erect, digitgrade (ankle held well off the ground) stance with feet postitioned directly below the body.
Similar eggshell microstructure.
Teeth with a constriction between the root and the crown.
Functional basis for wing power stroke present in arms and pectoral girdle (during motion, the arms were swung down and forward, then up and backwards, describing a "figure-eight" when viewed laterally).
Expanded pneumatic sinuses in the skull.
Five or more vertebrae incorporated into the sacrum (hip).
Straplike scapula (shoulder blade).
Clavicles (collarbone) fused to form a furcula (wishbone).
Hingelike ankle joint, with movement mostly restricted to the fore-aft plane.
Secondary bony palate (nostrils open posteriorly in throat).
Possibly feathers... this awaits more study. Small, possibly feathered dinosaurs were recently found in China. It appears that many coelurosaurs were cloaked in an external fibrous covering that could be called "protofeathers."
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