Unenlagia

*Unenlagia comahuensis*

***Unenlagia*** (meaning "half-bird" in Latinized Mapuche) was a genus of theropod dinosaur of the family Dromaeosauridae. *Unenlagia*, which lived in South America during the Late Cretaceous, was a member of the strange and extremely bird-like Gondwanan sub-family of dromaeosaurs called unenlagiines, and was closely related to dinosaurs such as *Buitreraptor* and *Neuquenraptor* (which might be the same species as *Unenlagia*). Makovicky *et al.* suggested that the 'flying raptor' *Rahonavis* is also 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*.

*Unenlagia* was very birdlike itself. Novas and Puerta found its pelvic region to be very similar to that of the early bird *Archaeopteryx*. The shoulder girdle of *Unenlagia* also shows adaptations for flapping. At 2 meters (6.6 ft long), *Unenlagia* was probably too big to fly; thus either it evolved from flying ancestors, or *Rahonavis* (if an unenlagiine) evolved flight from adequately adapted (but too large; *see also* exaptation) dromaeosaurs independently of the *Archaeopteryx* lineage, at a time when other bird lineages were already undergoing vigorous adaptive radiation.

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 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*.

## Description

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.

## Phylogeny

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:

## JPInstitute.com Description

Unenlagia is the most bird-like dinosaur found so far - it even had arms that were designed so they could flap like a bird's wings! However, this dinosaur was much too large to fly, but it clearly shows how some dinosaurs were evolving to look and act like modern birds. Some scientists think that Unenlagia is actually a young Megaraptor, as the fossils were found in the same area.

Unenlagia is from the same general family that also includes many of the dinosaurs that exhibited bird-like traits, including those falling into the popular raptor category. It had a very pronounced backward-pointing pubis, and it appears as though its shoulder was designed to allow for flapping movements.

## Links

https://web.archive.org/web/20030405114409/http://www.jpinstitute.com/dinopedia/dinocards/dc\_unenl.html

## References

1. ↑ 1.0 1.1 Makovicky, Apesteguía and Agnolín (2005). "The earliest dromaeosaurid theropod from South America." *Nature*, **437**: 1007–1011. Cite error: Invalid `<ref>` tag; name "makovickyetal2005" defined multiple times with different content
2. ↑ 2.0 2.1 Norell, M.A., Clark, J.M., Turner, A.H., Makovicky, P.J., Barsbold, R., and Rowe, T. (2006). "A new dromaeosaurid theropod from Ukhaa Tolgod (Omnogov, Mongolia)." *American Museum Novitates*, **3545**: 1-51. Cite error: Invalid `<ref>` tag; name "norelletal2006" defined multiple times with different content
3. ↑ Novas, F.E., and Puerta, P.F. (1997). "New evidence concerning avian origins from the Late Cretaceous of Patagonia." *Nature*, 387: 390-2.
4. ↑ Calvo, J.O., Porfiri, J.D. and Kellner, A.W. (2004). "On a new maniraptoran dinosaur (Theropoda) from the Upper Cretaceous of Neuquén, Patagonia, Argentina." *Arq. Mus. Nacional. Rio de Janeiro*, **62**: 549-566.
5. ↑ Template:Cite journal
6. ↑ M.A. Norell and P.J. Makovicky, 2004, "Dromaeosauridae". In: D.B. Weishampel, P. Dodson, and H. Osmolska (eds.), *The Dinosauria* (second edition). University of California Press, Berkeley pp. 196-209
7. ↑ Template:Cite journal
8. ↑ Template:Cite journal
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