title: An Unusual New Theropod with a Didactyl Manus from the Upper Cretaceous of Patagonia, Argentina.
abstract: BACKGROUND
  Late Cretaceous terrestrial strata of the Neuquén Basin, northern Patagonia, Argentina have yielded a rich fauna of dinosaurs and other vertebrates. The diversity of saurischian dinosaurs is particularly high, especially in the late Cenomanian-early Turonian Huincul Formation, which has yielded specimens of rebacchisaurid and titanosaurian sauropods, and abelisaurid and carcharodontosaurid theropods. Continued sampling is adding to the known vertebrate diversity of this unit.
  
  
  RESULTS
  A new, partially articulated mid-sized theropod was found in rocks from the Huincul Formation. It exhibits a unique combination of traits that distinguish it from other known theropods justifying erection of a new taxon, Gualicho shinyae gen. et sp. nov. Gualicho possesses a didactyl manus with the third digit reduced to a metacarpal splint reminiscent of tyrannosaurids, but both phylogenetic and multivariate analyses indicate that didactyly is convergent in these groups. Derived characters of the scapula, femur, and fibula supports the new theropod as the sister taxon of the nearly coeval African theropod Deltadromeus and as a neovenatorid carcharodontosaurian. A number of these features are independently present in ceratosaurs, and Gualicho exhibits an unusual mosaic of ceratosaurian and tetanuran synapomorphies distributed throughout the skeleton.
  
  
  CONCLUSIONS
  Gualicho shinyae gen. et sp. nov. increases the known theropod diversity of the Huincul Formation and also represents the first likely neovenatorid from this unit. It is the most basal tetatanuran to exhibit common patterns of digit III reduction that evolved independently in a number of other tetanuran lineages. A close relationship with Deltadromaeus from the Kem Kem beds of Niger adds to the already considerable biogeographic similarity between the Huincul Formation and coeval rock units in North Africa.
authors.affiliation: Área de Paleontología. Fundación de Historia Natural 'Félix de Azara', CEBBAD, Univ. Maimónides, Buenos Aires, Argentina.
authors.forename: Sebastián
authors.initials: S
authors.lastname: Apesteguía
authors.affiliation: Dinosaur Institute, Natural History Museum of Los Angeles County, Los Angeles, United States of America.
authors.forename: Nathan D
authors.initials: ND
authors.lastname: Smith
authors.affiliation: Secretaría de Cultura, Gobierno de la Provincia de Río Negro, General Roca, Argentina.
authors.forename: Rubén
authors.initials: R
authors.lastname: Juárez Valieri
authors.affiliation: Section of Earth Sciences, Integrative Research Center, Field Museum of Natural History, Chicago, Illinois, United States of America.
authors.forename: Peter J
authors.initials: PJ
authors.lastname: Makovicky
mesh_terms: D000818:Animals; D001118:Argentina; D049628:Body Size; D025061:Dinosaurs / Q000033:anatomy & histology* / Q000145:classification; D005552:Forelimb / Q000033:anatomy & histology; D005580:Fossils / Q000033:anatomy & histology; D008953:Models, Anatomic; D015999:Multivariate Analysis; D010163:Paleontology; D010802:Phylogeny; D013131:Spine / Q000033:anatomy & histology