A new theropod with a didactyl manus and African affinities from the Upper Cretaceous of Patagonia, Argentina

APESTEGUIA, S.; PETER J. MAKOVICKY; NATHAN SMITH; JUAREZ VALIERI, RUBÉN

Guanajuato

Congreso; 
VIII 
Congreso 
Latinoamericano
 de 
Paleontología 
& 
XIII 
Congreso
 Mexicano
 de 
Paleontología
; 2013

Universidad Autónoma de México - Universidad de Guanajuato

The Huincul Formation (Late Cenomanian-Early Turonian) is widely exposed in Northern Patagonia, Argentina. This unit has yielded the remains of some of the largest sauropod dinosaurs (e.g., $Argentinosaurus$) as well as a diversity of theropods including large carcharodontosaurids (e.g., $Mapusaurus$) and mid-sized abelisauroids (e.g., $Ilokelesia, Skorpiovenator$). A joint expedition to the area by the Fundación Azara and Field Museum of Natural History in 2007 discovered the partially articulated skeleton of a mid-sized theropod dinosaur. This specimen was subsequently excavated and prepared by the Museo Patagónico de Ciencias Naturales. The new specimen (MPCN Pv-001) exhibits a unique combination of traits that distinguish it from carcharodontosaurids and abelisaurids, and indeed other known theropods. It shares derived characters of the scapula, femur, and fibula with the nearly coeval African theropod $Deltadromaeus$ from the Kem Kem beds of Niger, though differing in the relative length and shape of the humerus. $Deltadromaeus$ has recently been reinterpreted as a basal ceratosaurian, but since MPCN Pv-001 lack a ceratosaur-like bulbous humeral head, and actually possesses a distinctly tetanuran hand morphology, with the reduction pattern of megaraptorans and tyrannosauroids, the possible sister taxon relationship with MPCN Pv-001 results complicated. However, a sister taxon relationship between MPCN Pv-001 and $Deltadromaeus$ is not unexpected, as the Neuquén Group units share a wide number of taxa with the Kem Kem beds and their equivalents, including carcharodontosaurids, abelisaurids, ?noasaurids?, possibly dromaeosaurids, rebacchisaurid sauropods, and crocodylomorphs. Whether these faunal similarities reflect biogeographic history such as recent vicariance, or represent habitat tracking is unknown at present, but it remains a recurrent pattern worthy of further study.