Open Paleo

Unquillosaurus

Powell, 1979 oong-KEE-yo-SAWR-us

Named for the Unquillo River of Salta Province, Argentina, combined with Greek 'sauros' meaning 'lizard'.

83.6–66.0 million years ago Campanian–Maastrichtian, Late Cretaceous
Late Cretaceous stages

Unquillosaurus 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, though a carcharodontosaurid position has also been argued from the same bone. The genus contains a single species, U. ceibalii, known only from a single fossilized pubis (a pelvic bone).

Under dispute

Unquillosaurus ceibalii is known only from a single pubis, and its affinities have moved with each rereading of that bone. Powell (1979) took it for a carnosaur; Novas and Agnolín (2004) emended the diagnosis and argued from the pubis for a position within Metornithes, close to Paraves; Carrano and colleagues (2012) recovered it as a carcharodontosaurid; and Agnolín and Novas (2013), rejecting that referral, judged it probably a very large averaptoran, from comparison rather than a scored analysis. What is contested is where it belongs, not whether the bone is diagnosable. It sits at Avetheropoda incertae sedis, the nearest node all four readings share.

Diagnosis

  1. Pubis proportionally long and slender, and at 51.4 cm longer than in basal maniraptorans such as Deinonychus and Unenlagia
  2. Pubic shaft craniocaudally compressed over its proximal three quarters rather than rod-like, raising a prominent longitudinal ridge on the external surface
  3. Compression of the proximal shaft giving way to craniocaudal expansion distally, twisting the bone along its length, where most theropods have nearly parallel shaft margins
  4. Margins of the pelvic canal medially convex, against the medially concave margins of most theropods
  5. Pubic shaft without an apron and lacking a medial symphysis, contact with the opposite bone reduced to a medially flattened distal end that bears no articular marks
  6. Apex of the caudal process of the pubic foot curved dorsally, a condition absent in other theropods

Species

Unquillosaurus ceibalii Powell, 1979

Type species

Named for the town El Ceibal, near the site where the holotype was found.

Holotype
PVL 3670-11 , Colección de Paleontologia de Vertebrados de la Fundación Instituto Miguel Lillo
Material
Almost complete left pubis, with a broken fragment of the ilium's pubic pedicle adhered to the external surface of its proximal end.
Horizon
upper Los Blanquitos Formation, Campanian–Maastrichtian, Late Cretaceous , 83.6–66.0 million years ago
Locality
Arroyo Morterito, Salta, Argentina

References

  1. Powell, J. E. (1979). Sobre una asociacion de Dinosaurios y otras evidencias de vertebrados del Crétacico Superior de la region de La Candelaria, Prov. de Salta, Argentina [On an assemblage of dinosaurs and other vertebrate evidence from the Upper Cretaceous of the La Candelaria region, Salta Province, Argentina]. Ameghiniana 16(1-2): 191-204. powell1979a
  2. Jones, B. (2026). The Princeton Encyclopedia of Dinosaurs: Theropods. Princeton University Press.

    Source of the body length estimate.

    jones2026c
  3. Carrano, M. T.; Benson, R. B. J.; Sampson, S. D. (2012). The phylogeny of Tetanurae (Dinosauria: Theropoda). Journal of Systematic Palaeontology 10(2): 211-300. Informa UK Limited. doi:10.1080/14772019.2011.630927

    Tetanurae phylogeny placed Unquillosaurus as a carcharodontosaurid based on its pubis.

    carrano2012a
  4. Novas, F. E.; Agnolín, F. L. (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

    Emends the diagnosis from the holotype pubis and argues from its characters for a position within Metornithes, close to Paraves, against Powell's reading of the bone as a carnosaur's.

    novas2004c
  5. Agnolín, F. L.; Novas, F. E. (2013). Avian Ancestors. SpringerBriefs in Earth System Sciences. Springer Netherlands. doi:10.1007/978-94-007-5637-3

    Rejects the carcharodontosaurid referral and judges Unquillosaurus probably a very large averaptoran, from comparison rather than a scored analysis.

    agnolín2013a