An unusual new theropod with a didactyl manus from the upper cretaceous of patagonia, Argentina

Sebastián Apesteguía, Nathan D. Smith, Rubén Juárez Valieri, Peter J. Makovicky

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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. Methodology/ Principal Findings 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/ Significance 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.

Original languageEnglish (US)
Article numbere0157793
JournalPloS one
Issue number7
StatePublished - Jul 2016
Externally publishedYes

Bibliographical note

Funding Information:
We are grateful to Akiko Shinya, Alejandro Otero, Pablo Gallina, Jorge González, and Attila Ősi for assistance in the field, and to Juan Ignacio Canale and Alejandro Haluza for their assistance and hospitality in El Chocón. Rodolfo Coria, Philip Currie, and Hussam Zaher are thanked for discussions surrounding the provenance and history of excavation and preparation of the specimen. PJM and NDS are grateful to Pablo Chafrat for specimen access. Fieldwork that resulted in the discovery of the holotype of Gualicho shinyae was supported by a generous gift from Michael and Jacqueline Ferro through the Women’s Board of The Field Museum. PJM and NDS were supported by grants from the US National Science Foundation over the course of this work (EAR 0228607; ANT 0838925; PLR 1246379; and EAR 1349554). SA was supported by CONICET. A single user copy of TNT used for this research was provided free through the generous support of the Willi Hennig Society. Diego Pol is thanked for his assistance in modifying the 'Term_length' script to include all taxa, and Sushma Reddy is thanked for assistance with R scripting.

Publisher Copyright:
© 2016 Apesteguía et al. This is an open access article distributed under the terms of the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original author and source are credited.


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