Falcarius is known from multiple specimens at different ontogenic stages. While the smallest specimen was approximately less than , average adults were about in length weighing approximately .
Skull The head anatomy of
Falcarius is partially known. The skull was small and elongated. With its long neck,
Falcarius could apparently reach about off the ground to munch leaves or fruit, possibly higher. The teeth numbered at least sixteen in the
maxilla of the upper jaw. The
dentary (part of the lower jaw) carried twenty-eight
teeth. Its small leaf-shaped and very finely serrated maxillary teeth indicate that it consumed plant material. The front-most five teeth of the lower jaw are much longer, straighter and more pointed though, and might indicate a partially omnivorous diet including meat, e.g. small animals such as
lizards. In the back of the head, the braincase was relatively large. Its lower elements were moderately inflated by pneumatised, hollowed-out, bone tissue. The large skull opening in the snout, the
fenestra antorbitalis, is positioned in a depression which reaches the side of the
nasal bone. There are at least five pairs of conical teeth in the front of the lower jaws. These teeth are hollowed-out at the inside. On the underside of the vertebrae of the neck there is a depression with at the mid-line a ridge. On the underside of the braincase there is a well-developed depression, the
recessus basisphenoidalis. At the back of the head there are deep depressions below the
occipital condyle and on the subotics, each with several pneumatic grooves.
Postcranial skeleton The partitioning of the vertebral column followed that of most maniraptorans. The neck was very long with elongated cervical vertebrae. The tail was relatively long. The arm was moderately long with a somewhat robust
humerus. The relatively large, and slightly recurved, pointed ten- to thirteen-centimeter (four- to five-inch) hand claws were likely used in self-defence.
Falcarius is known from many specimens, including complete forelimb specimens. Most of the bones of the pectoral girdle and forelimb are known, although sternal bones are not preserved. Both a left and right scapula are preserved, and they are both mostly complete as well. The blades of the scapulae are about long, and also quite slender, with barely any expansion. They are curved instead of straight. The scapula is placed in a relatively high position. Two coracoids are also preserved, although they differ more than the scapulae in morphology. The right coracoid is the better preserved of the two. The coracoid is not specially enlarged. The
furcula is elongated and narrow, its branches placed at an angle of 104°. It is V-shaped and possesses a small hypocleidium at the front. The arm as a whole is not especially developed in length but shows signs of an increasing robustness. The humerus has a rather short triangular deltopectoral crest. The epicondyles are exceptionally thick, indicating a strong musculature. The
ulna is lightly curved. (or hallux) The hand is rather long but not very robust, with in general an elongated
metacarpus, although the first
metacarpal is short. The first finger diverges from the second finger, the longest of the hand. The third finger is very thin. The hand claws are moderately curved, rather pointed, and moderately long. The vertebrae of the back have below their front extensions, the
prezygapophyses, a groove which is divided in three smaller depressions. On the thumb claw the raised attachment point for the tendon of the extensor muscle is bordered by deep grooves for
ligaments. The middle vertebrae of the back have a second ridge extending from the base of the upper rib joint, the
diapophysis, to the back of the vertebra. In the arm, the shaft of the
humerus is reinforced by powerful, somewhat obliquely placed, thickenings extending towards the
condyles of the lower joint, which swellings have a hollow front edge. The front edge of the hip joint has a prominent swelling, pointing sideways to the back, on the
pubis. In the pelvis the
ilium was by a moderate inclination partly adapted to a more raised position of the trunk. The pelvis was propubic or mesopubic: the
pubic bone pointed more or less forwards. The leg was relatively long and adapted to running, with the lower leg longer than the thighbone. In the foot there were three weight-bearing toes. The first toe did not reach the ground nor did the first
metatarsal touch the ankle. ==Classification==