Unenlagia

Unenlagia (meaning "half-bird" in Latinized Mapudùngun) is a genus of dromaeosaurid theropod dinosaur that lived in South America during the Late Cretaceous period.[1] The genus Unenlagia has been assigned two species: U. comahuensis, the type species described by Novas and Puerta in 1997,[1] and U. paynemili, described by Calvo et al. in 2004.[2]

This article is about the dinosaur. For the Zoid by the same name, see Unenlagia (Zoids).

Unenlagia
Temporal range: Late Cretaceous
~89 Ma
↓
Casts of U. paynemili fossils; today the claw is considered one of the hand unguals, not of the foot as shown here
Scientific classification
Kingdom: Animalia
Phylum: Chordata
Clade: Dinosauria
Clade: Saurischia
Clade: Theropoda
Family: †Unenlagiidae
Subfamily: †Unenlagiinae
Genus: †Unenlagia
Novas & Puerta, 1997
Species
  • †U. comahuensis Novas & Puerta, 1997 (type)
  • †U. paynemili Calvo, Porfiri & Kellner, 2004

Discovery and naming
Illustration of known material of U. comahuensis

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.[3] 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.[1]

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.[1]

In 2002 near the Lago Barreales a second skeleton was uncovered and reported in 2003.[4] 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.[2]

Some researchers consider Neuquenraptor to be a junior subjective synonym of Unenlagia.[5]

Description
Size comparison with a 1.7 m tall human

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.[1] Estimates have thus varied between a length of 3.5 m (11 ft) and a weight of 75 kg (165 lb) on the one hand,[6] and a length of just 2 m (6.6 ft) on the other.[7] However, Thomas Holtz has estimated Unenlagia at 2.3 m (7.5 ft) long and 9.1-22.7 kg (20-50 lbs) in weight.[8] 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.

Restoration 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.[1] 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.[1] 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.[9] 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.[10] 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.[7]

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.[11][12] 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.[13] Norell et al. in 2006 also found Rahonavis to be the sister taxon of Unenlagia.[14]

This position has not been unanimously accepted. In 2011 Novas and Federico Agnolín published a study in which an Unenlagiidae was positioned within Avialae.[15]

Below is a cladogram conducted by Hartman et al. 2019, in which Unenlagia is found to be a more derived member alongside Dakotaraptor:[16]

Unenlagiinae
 

Austroraptor

 
 
 

Buitreraptor

 
 
 

Pyroraptor

 
 

Pamparaptor

 
 
 

Rahonavis

 
 
 

Dakotaraptor

 
 

Unenlagia

 
 
 
 
 
 

See also

References
  1. Novas, F.E.; Puerta, P.F. (1997). "New evidence concerning avian origins from the Late Cretaceous of Patagonia". Nature. 387 (6631): 390–2. Bibcode:1997Natur.387..390N. doi:10.1038/387390a0. S2CID 4353732.
  2. Calvo, J.O.; Porfiri, J.D.; 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.
  3. F.E. Novas, G. Cladera, and P. Puerta, 1996, "New theropods from the Late Cretaceous of Patagonia", Journal of Vertebrate Paleontology 16(3, suppl.):56A
  4. Calvo, J.O., Porfiri, J.D. and Kellner, A.W.A., 2003, "A close relative of Unenlagia comahuensis (Theropoda, Maniraptora) from the Upper Cretaceous of Neuquén, Patagonia, Argentina", 18º Congresso Brasileiro de Paleontologia, Brasilia, Resumos: 82-83
  5. A. H. Turner, S. H. Hwang, and M. A. Norell. 2007. "A small derived theropod from Öösh, Early Cretaceous, Baykhangor Mongolia". American Museum Novitates 3557: 1-27
  6. Paul, G. S. (2010). The Princeton Field Guide to Dinosaurs. Princeton University Press. p. 138.
  7. Gianechini, F. A.; Apesteguía, S. (2011). "Unenlagiinae revisited: Dromaeosaurid theropods from South America". Anais da Academia Brasileira de Ciências. 83 (1): 163–95. doi:10.1590/S0001-37652011000100009. PMID 21437380.
  8. Holtz, T. R.; Rey, L. V. (2007). Dinosaurs: The Most Complete, Up-to-Date Encyclopedia for Dinosaur Lovers of All Ages. Random House. Supplementary Information 2012 Weight Information
  9. Carpenter, K. 2002. "Forelimb biomechanics of nonavian theropod dinosaurs in predation". Senckenbergiana Lethaea 82: 59–76
  10. Senter, P. (2006). "Scapular orientation in theropods and basal birds, and the origin of flapping flight." Acta Palaeontologica Polonica, 51(2): 305–313.PDF fulltext
  11. Norell, M.A.; Makovicky, P.J. (1999). "Important features of the dromaeosaur skeleton II: information from newly collected specimens of Velociraptor mongoliensis". American Museum Novitates. 3282: 1–45.
  12. 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
  13. Makovicky PJ, Apesteguía S, Agnolín FL (2005). "The earliest dromaeosaurid theropod from South America". Nature. 437 (7061): 1007–1011. Bibcode:2005Natur.437.1007M. doi:10.1038/nature03996. PMID 16222297. S2CID 27078534.
  14. Norell, M.A.; Clark, J.M.; Turner, A.H.; Makovicky, P.J.; Barsbold, R.; Rowe, T. (2006). "A new dromaeosaurid theropod from Ukhaa Tolgod (Omnogov, Mongolia)". American Museum Novitates. 3545: 1–51. doi:10.1206/0003-0082(2006)3545[1:ANDTFU]2.0.CO;2. hdl:2246/5823.
  15. Agnolin, F.L.; Novas, F.E. (2011). "Unenlagiid theropods: are they members of the Dromaeosauridae (Theropoda, Maniraptora)?". Anais da Academia Brasileira de Ciências. 83 (1): 117–162. doi:10.1590/S0001-37652011000100008. PMID 21437379.
  16. Hartman, S.; Mortimer, M.; Wahl, W. R.; Lomax, D. R.; Lippincott, J.; Lovelace, D. M. (2019). "A new paravian dinosaur from the Late Jurassic of North America supports a late acquisition of avian flight". PeerJ. 7: e7247. doi:10.7717/peerj.7247. PMC 6626525. PMID 31333906.
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