The genus Unenlagia has been assigned two species: U. comahuensis, the type species described by Novas and Puerta in 1997, and U. paynemili, described by Calvo et al. in 2004.
Discovery and namingEdit
In 1996 in the Neuquén province of Argentina a skeleton of a theropod was discovered in the Sierra del Portezuelo and reported the same year. In 1997 Fernando Emilio Novas and Pablo Puerta named and described Unenlagia comahuensis. The generic name is derived from Mapuche uñen, "half", and lag, "bird", in reference to the fact that the describers considered the species to be a link between birds and more basal theropods. The specific name refers to the Comahue, the region the find was made.
The holotype specimen, MCF PVPH 78, was uncovered in layers of the Portezuelo Formation dating to the Coniacian. It consists of a partial skeleton lacking the skull but including vertebrae, a sacrum, ribs, chevrons, a scapula, a humerus, a partial pelvis, a femur and a tibia.
In 2002 near the Lago Barreales a second skeleton was uncovered and reported in 2003. In 2004 it was named and described by Jorge Calvo, Juan Porfiri and Alexander Kellner as a second species: Unenlagia paynemili. The specific name honours Maximino Paynemil, the chief of the Paynemil community. The holotype is MUCPv-349, a partial skeleton consisting of a humerus and two pubes. Several paratypes were also assigned: MUCPv-343, a claw; MUCPv-409, a partial ilium; MUCPv-415, a phalanx and MUCPv-416, a vertebra.
Some researchers consider Neuquenraptor to be a junior subjective synonym of Unenlagia.
The body length of Unenlagia has been disputed, due to the fact that only the leg length is well known and an uncertainty whether this should be extrapolated using the proportions of the low-slung Dromaeosauridae or the long-legged basal birds. Estimates have thus varied between a length of 3.5 metres and a weight of 75 kilogrammes on the one hand, and a length of just two metres on the other. 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.
Unenlagia was very birdlike. Novas and Puerta found its pelvic region, especially the form of the ilium, to be 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. However, in 2002 Kenneth Carpenter pointed out that this would imply that the shoulder-blade was dorsoventrally flattened instead of laterally as with other theropods and that it thus were more likely the scapula was located on the side of the ribcage. 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.
At at least two meters (6.6 ft long), Unenlagia was probably too big to fly; scientists thus consider that it either evolved from flying ancestors, or Rahonavis (if an unenlagiine) evolved flight from adequately pre-adapted (but too large; see also exaptation) dromaeosaurids independently of the Archaeopteryx lineage, at a time when a multitude of bird lineages had already undergone vigorous adaptive radiation.