The body length of
Unenlagia has been disputed, due to the fact that only the leg length is well known and it is uncertain whether this should be extrapolated using the proportions of the low-slung Dromaeosauridae or the long-legged basal birds. and a length of just on the other. However, Thomas Holtz has estimated
Unenlagia at long and 9.1-22.7 kg (20-50 lbs) in weight. The describers of
Austroraptor estimated that
Unenlagia reached over long and weighed about . Likewise, the interpretation of the head form has changed from a shorter-snouted dromaeosaurid condition to the elongated shape known from the later discovered related genera
Buitreraptor and
Austroraptor. of
U. comahuensis Novas and Puerta found that the pelvic region of
Unenlagia, especially the form of the
ilium, was very similar to that of the early bird
Archaeopteryx. The shoulder girdle of
Unenlagia was originally interpreted as if it was adapted for flapping, with a flat
scapula positioned on top of the ribcage, making the shoulder joint point more laterally. This conformed to a later hypothesis by
Philip Senter that non-avian theropods like
Unenlagia were unable to lift their forelimbs above their back, as even would still have been the case for the basalmost bird
Archaeopteryx. South American workers have remained unconvinced though, countering that a laterally positioned scapula would make the
coracoid of
Unenlagia jut into its ribcage, which seems anatomically implausible. ==Classification==