Unenlagia

''Unenlagia'' (meaning "half-bird" in Latinized Mapudungun) is a genus of dromaeosaurid theropod dinosaur that lived in South America during the Late Cretaceous period. 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 naming

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 ''uñùm'', 'bird', and ''llag'', 'half', 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''.

Description

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. Estimates have thus varied between a length of and a weight of on the one hand, 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. 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''.

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. 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''.Senter, P. (2006). "Scapular orientation in theropods and basal birds, and the origin of flapping flight." ''Acta Palaeontologica Polonica'', 51(2): 305–31
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/ref> 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

Novas and Puerta in the original description considered ''Unenlagia'' a sister taxon of the birds, which would make it a basal member of the Avialae ''sensu'' Gauthier 1986.

However, in 1999 Mark Norell and Peter Makovicky stated that ''Unenlagia'' was a member of the Dromaeosauridae. ''Unenlagia'' would have belonged to the extremely bird-like Gondwanan clade of dromaeosaurids called the Unenlagiinae, and be closely related to species such as '' Buitreraptor'' and '' Neuquenraptor'' (which might be the same species as ''Unenlagia''). Makovicky ''et al.'' in 2005 also recovered the 'flying raptor' ''Rahonavis'' as a member of this group, which would mean that either ''Unenlagia'' is secondarily flightless, having evolved from flying, ''Rahonavis''-like ancestors, or that bird-like flight evolved at least twice. Norell ''et al.'' in 2006 also found ''Rahonavis'' to be the sister taxon of ''Unenlagia''.

This position has not been unanimously accepted. In 2011 Novas and Federico Agnolín published a study in which a Unenlagiidae was positioned within Avialae.

Below is a cladogram conducted by Hartman et al. 2019, in which ''Unenlagia'' is found to be a more derived member alongside ''Dakotaraptor'':

This cladogram is from Motta ''et al.'', 2020, showing ''Unenlagia'' being more derived than traditional dromaeosaurids:

See also

* Timeline of dromaeosaurid research
* Origin of birds

''Unenlagia'' in the Dino Directory

References

{{Taxonbar, from=Q134159

Unenlagiines
Coniacian life
Late Cretaceous dinosaurs of South America
Cretaceous Argentina
Fossils of Argentina
Portezuelo Formation
Fossil taxa described in 1997
Taxa named by Fernando Novas