Noasaurus

Noasaurus; Temporal range: Late Cretaceous, 70 Ma PreꞒ Ꞓ O S D C P T J K Pg N ↓
	Skeletal restoration showing known remains
Scientific classification
Domain:	Eukaryota
Kingdom:	Animalia
Phylum:	Chordata
Clade:	Dinosauria
Clade:	Saurischia
Clade:	Theropoda
Family:	†Noasauridae
Genus:	†Noasaurus; Bonaparte & Powell, 1980
Species:	†N. leali
Binomial name
	†Noasaurus leali; Bonaparte & Powell, 1980

Noasaurus ("Northwestern Argentina lizard") is a genus of carnivorous theropod dinosaur genus of the late Campanian-Maastrichtian (Late Cretaceous).

Discovery and naming

In the mid-seventies, a fragmentary small theropod skeleton was discovered by Jaime Eduardo Powell and José Fernando Bonaparte at the Estancia El Brete-site. In 1977, the discovery was reported in the scientific literature.^[1] The type species, Noasaurus leali, was named and described by Bonaparte and Powell in 1980. The generic name begins with a usual abbreviation of noroeste Argentina, "northwest Argentina". The specific name honours the owner of the site, Fidel Leal.^[2]

The holotype, PVL 4061, was found in a layer of the Lecho Formation of Salta Province, Argentina, dating from the late Cretaceous period, more precisely the early Maastrichtian stage, about seventy million years ago. It consists of a partial skeleton with skull. It contains the maxilla, the quadrate bone, two neck vertebrae, two neck ribs, the centrum of a back vertebra, two hand claws, a finger phalanx and the second right metatarsal bone. One of the hand claws was initially identified as a second toe claw.^[2] In 2004, it was recognised as a hand claw, at which occasion the second hand claw was referred.^[3]

In 1999, a neck vertebra found at the site, specimen MACM 622, was identified as oviraptorosaurian, a rare proof that the Oviraptorosauria had invaded the Gondwanan continents.^[4] In 2007 however, it was reidentified as a noasaurid vertebra, probably belonging to the Noasaurus holotype.^[5]

Description

Noasaurus was a small theropod. Its length has been estimated at 1.5 metres, its weight at fifteen kilogrammes.^[6]

The maxilla bears at least eleven teeth. The teeth are recurved and have serrations at the front and rear edges.^[2]

The neck is probably long as the neck vertebrae are very elongated. These vertebrae are also strongly vertically compressed with a low neural spine and bear long epipophyses, a typical abelisauroid trait.^[5]

While originally reported to have a raptorial 'sickle claw' on the foot similar to the claws of the more advanced dromaeosaurids,^[2] subsequent studies showed that the claw actually came from the hand.^[7] The claw is exceptionally curved, has parallel base sides in top view, and possesses a deep triangular cavity at the base underside.^[3]

Classification

Noasaurus is today considered to be a member of the Ceratosauria. Originally, it was seen as a member of the Coelurosauria. Bonaparte and Powell assigned it to a family of its own, the Noasauridae.^[2] In 1988, Gregory S. Paul saw them as members of the Abelisauridae and coined a Noasaurinae within that group. He also incorrectly thought they were Megalosauria.^[6] Later, the noasaurids were recognised as close relatives of the larger abelisaurids; they are both derived from the same basal abelisauroid ancestor.

The following cladogram is based on the phylogenetic analysis conducted by Rauhut and Carrano in 2016, showing the relationships of Elaphrosaurus among the noasaurids:^[8]

	CCG 20011

	Elaphrosaurus

Noasaurinae

	Velocisaurus

	Noasaurus

	Masiakasaurus

Paleobiology

In 1980, it was thought that the presumed foot claw functioned as a sickle claw.^[2] Paul in 1988 saw the noasaurines as the South-American counterparts of the Asian and North-American dromaeosaurids, in a process of convergent evolution. Noting that abelisaurids tend to have very short arms, he wondered whether the forelimbs of Noasaurus were of limited length also, forcing the animal to employ a kicking technique instead of grasping the back of a victim in order to disembowel it with the foot claws, a method he assumed the dromaeosaurids used.^[6]This hypothesis was undermined when it was determined that the foot claw was in fact a hand claw.^[7]

In 2001, a more complete genus of noasaurid, Masiakasaurus was discovered. This genus had an unusual down-turned jaw which supposedly was an adaptation for piscivory (a diet of fish), suggesting that Noasaurus was similar in appearance and lifestyle.^[9]

References

^ Bonaparte, J.F., Salfitty, J.A., Bossi, G., Powell, J.E. 1977. "Hallazgos de dinosaurios y aves cretácicas en la Formación Lecho de El Brete (Salta), próximo al límite con Tucumán". Acta Geológica Lilloana 14: 19-28
^ ^a ^b ^c ^d ^e ^f J. F. Bonaparte and J. E. Powell. 1980. "A continental assemblage of tetrapods from the Upper Cretaceous beds of El Brete, northwestern Argentina (Sauropoda-Coelurosauria-Carnosauria-Aves)". Mémoires de la Société Géologique de France, Nouvelle Série 139: 19-28
^ ^a ^b Agnolin, F.L., Apesteguia, S. and Chiarelli, P. 2004. "The end of a myth: The mysterious ungual claw of Noasaurus leali". Journal of Vertebrate Paleontology. 24(3): 301A-302A
^ Frankfurt, N.G. and Chiappe, L.M. 1999. "A possible oviraptorosaur from the Late Cretaceous of northwestern Argentina". Journal of Vertebrate Paleontology. 19(1): 101-105
^ ^a ^b Agnolin, F.L. and Martinelli, A.G. 2007. "Did oviraptorosaurs (Dinosauria; Theropoda) inhabit Argentina?", Cretaceous Research, 28(5): 785-790
^ ^a ^b ^c Paul, G.S., 1988, Predatory Dinosaurs of the World. Simon & Schuster, New York, p 285-286
^ ^a ^b Agnolin, F.L. and Chiarelli, P. (2010). "The position of the claws in Noasauridae (Dinosauria: Abelisauroidea) and its implications for abelisauroid manus evolution." Paläontologische Zeitschrift, published online 19 November 2009. doi:10.1007/s12542-009-0044-2
^ Rauhut, O.W.M., and Carrano, M.T. (2016). The theropod dinosaur Elaphrosaurus bambergi Janensch, 1920, from the Late Jurassic of Tendaguru, Tanzania. Zoological Journal of the Linnean Society, (advance online publication) doi:10.1111/zoj.12425
^ Carrano, Matthew T.; Loewen, Mark A.; Sertich, Joseph J.W. (2011). "New materials of Masiakasaurus knopfleri Sampson, Carrano, and Forster, 2001, and implications for the morphology of the Noasauridae (Theropoda: Ceratosauria)" (PDF). Smithsonian Contributions to Paleobiology. 95. doi:10.5479/si.00810266.95.1.