Unquillosaurus

Unquillosaurus Temporal range: Maastrichtian ~72 Ma[1] PreꞒ Ꞓ O S D C P T J K Pg N ↓
Scientific classification
Domain:	Eukaryota
Kingdom:	Animalia
Phylum:	Chordata
Clade:	Dinosauria
Clade:	Saurischia
Clade:	Theropoda
Clade:	Maniraptoriformes
Clade:	Maniraptora
Genus:	†Unquillosaurus Powell, 1979
Species:	†U. ceibalii
Binomial name
†Unquillosaurus ceibalii Powell, 1979

Unquillosaurus (meaning "Unquillo river lizard") is a genus of large theropod dinosaur from the Late Cretaceous Los Blanquitos Formation of Salta Province, Argentina. Its precise classification is uncertain, but most researchers consider it as a maniraptoran. The genus contains a single species, U. ceibalii, known only from a single fossilized pubis (a pelvic bone).

Discovery and naming

The holotype, PVL 3670-11, was found at Arroyo-Morterito in the Los Blanquitos Formation, dating to the Maastrichtian.^[1] The specimen, which consists of a left pubis measuring 51.4 centimetres (1 ft 8.2 in) long, was re-studied by Fernando Novas and Federico Agnolin in 2004, who concluded that the orientation of the pubis had been misinterpreted: it pointed backwards, as was shown by the fossil still being attached to a displaced part of the pubic peduncle of the ilium.^[1]

The type species Unquillosaurus ceibalii was described by Jaime Eduardo Powell in 1979. The generic name, "Unquillosaurus," is derived from the river Unquillo and the Greek word, "sauros," meaning "lizard." The specific name, "ceibalii," refers to the town El Ceibal.^[2]

Classification

Powell originally assigned Unquillosaurus as a large theropod of uncertain taxonomic placement.^[2] In 2004, Novas and Agnolín concluded from the opisthopubic pelvic anatomy that Unquillosaurus was part of the Maniraptora or at least Maniraptoriformes, and likely closely related to either the Avialae or the bird-like Alvarezsauridae; perhaps it was itself a bird, a basal member of the Metornithes.^[1] In 2006, Martínez and Novas stated that Unquillosaurus probably belonged to the maniraptoran clade Dromaeosauridae.^[3] In 2012, however, Carrano and colleagues considered Unquillosaurus as a member of the Carcharodontosauridae, noting that the animal has many similarities to Giganotosaurus.^[4] In 2013, Agnolín and Novas interpreted Unquillosaurus as a very large averaptoran instead, suggesting that the distal pubis shows condition of a coelurosaur and different from that of a carnosaur.^[5] In a 2016 study about the phylogeny of theropods found in Argentina, Unquillosaurus is considered as a maniraptoran.^[6] As of the 2020s, no reliable records of carcharodontosaurids beyond the Turonian age were known.^[7]

Paleoecology

Unquillosaurus is known from the Los Blanquitos Formation. The abelisaurid theropod Guemesia is also known from this formation,^[8] as well as fossils of what may belong to a species of Titanosaurus.^[9]

See also

• Timeline of dromaeosaurid research

References

1. Novas, F.E.; Agnolín (2004 (2004). "Unquillosaurus ceibalii Powell, a giant maniraptoran (Dinosauria, Theropoda) from the Late Cretaceous of Argentina". Revista del Museo Argentino de Ciencias Naturales. 6 (1): 61–66. doi:10.22179/REVMACN.6.73.
2. Powell, J.E. (1979). "On a dinosaur association and other evidinces of Upper Cretaceous vertebrates from the La Candelaria region, Salta Province, Argentina". Ameghiniana. 16 (1–2): 191–204. S2CID 126995364.
3. R.D. Martínez and F.E. Novas, 2006, "Aniksosaurus darwini gen. et sp. nov., a new coelurosaurian theropod from the early Late Cretaceous of central Patagonia, Argentina", Revista del Museo Argentino de Ciencias Naturales, nuevo serie 8(2): 243-259
4. Carrano, Matthew T.; Benson, Roger B.J.; Sampson, Scott D. (2012). "The phylogeny of Tetanurae (Dinosauria: Theropoda)". Journal of Systematic Palaeontology. 10 (2): 211–300. Bibcode:2012JSPal..10..211C. doi:10.1080/14772019.2011.630927. S2CID 85354215.
5. Agnolín, Federico L.; Novas, Fernando E. (2013), "Uncertain Averaptoran Theropods", Avian Ancestors, Dordrecht: Springer Netherlands, pp. 37–47, doi:10.1007/978-94-007-5637-3_4, ISBN 978-94-007-5636-6, retrieved 2022-03-17
6. Ezcurra, M.D.; Novas, F.E. (2016). "Theropod dinosaurs from Argentina" (PDF). Museo Argentino de Ciencias Naturales Bernardino Rivadavia: 139–156. ISSN 1666-5503.
7. Meso, J.G.; Juárez Valieri, R.D.; Porfiri, J.D.; Correa, S.A.S.; Martinelli, A.G.; Casal, G.A.; Canudo, J.I.; Poblete, F.; Dos Santos, D. (2021-09-01). "Testing the persistence of Carcharodontosauridae (Theropoda) in the Upper Cretaceous of Patagonia based on dental evidence". Cretaceous Research. 125: 104875. Bibcode:2021CrRes.12504875M. doi:10.1016/j.cretres.2021.104875. hdl:11336/183886. ISSN 0195-6671.
8. Agnolín, Federico L.; Cerroni, Mauricio A.; Scanferla, Agustín; Goswami, Anjali; Paulina-Carabajal, Ariana; Halliday, Thomas; Cuff, Andrew R.; Reuil, Santiago (2022-02-10). "First definitive abelisaurid theropod from the Late Cretaceous of Northwestern Argentina". Journal of Vertebrate Paleontology. 41 (4): e2002348. doi:10.1080/02724634.2021.2002348. ISSN 0272-4634. S2CID 246766133.
9. Arroyo El Morterito at Fossilworks.org