A new furileusaurian abelisaurid from La Invernada (Upper Cretaceous, Santonian, Bajo de la Carpa Formation), northern Patagonia, Argentina

ABSTRACT

Abelisaurids are among the most abundant and diverse Patagonian Late Cretaceous theropods. Here, we present a new furileusaurian abelisaurid, Llukalkan aliocranianus gen. et sp. nov., represented by cranial remains from the Bajo de la Carpa Formation (Santonian) at La Invernada fossil area, northwestern Patagonia. Features characterizing this taxon include a possible caudal tympanic recess posterior to the columellar recess, a T-shaped lacrimal with jugal ramus lacking a suborbital process, and large foramina for caudal middle cerebral veins widely separated from the median supraoccipital crest. In addition to this, a bulge on the anteromedial border of the supratemporal fossa, tall and posteriorly projected paroccipital processes, basal tubera interconnected distally, a triangular basisphenoid recess, and a single foramen for the sphenoidal artery on the basisphenoid, differentiate Llukalkan from Viavenator exxoni. The latter is the other furileusaurian taxon from the same area and stratigraphic unit. Although the holotype of Llukalkan probably corresponds to a sub-adult—as the lacrimal morphology suggests— the possibility that it represents a juvenile of V. exxoni is discarded based mainly on the presence of a caudal tympanic recess (which is absent in V. exxoni). The probable coexistence of two abelisaurid taxa demonstrates that the abelisaurids were one of the most important—and likely the main—predator component of the ecosystems, not only in this area, but also in all of Patagonia, during the Late Cretaceous.

ACKNOWLEDGMENTS

We are grateful to ExxonMobil for financing the 2015 fieldwork in which the materials of the new taxon were discovered and exhumed; to the Museo Municipal ‘Argentino Urquiza’ technicians, S. Palomo, C. Fuentes, and A. Schenkel, who were part of the field crew and who prepared the specimen; to the Municipalidad de Rincón de los Sauces for the logistic assistance in fieldwork and transport of the materials. We deeply thank Dr. G. Bianchi and Clínica Moguillanski for allowing the CT scanning of the specimen. We would also like to thank E. Ruigómez (MPEF) for the access to specimens under his care. A special thank you is for O. Ratsimbaholison for kindly sharing photographs and information of Majungasaurus and for useful discussions and comments about the morphology of this taxon. A. Haro, M. Baiano, and D. Pérez kindly helped us with some aspects of the phylogenetic analyses. We are also grateful for the comments and suggestions of R. Delcourt and M. Carrano, who helped us to improve the quality of this work; R. Delcourt also provided us with photographs of Rugops. Many thanks to staff of the GAECI (Gabinete de Asesoramiento en Escritura Científica en Inglés, Universidad Nacional de San Luis) for their assistance with the language revision of the manuscript. This work was also supported by funds of the Fondo para la Investigación Científica y Tecnológica PICT 2014-1449 (to FAG), PICT 2015-0920 (to AHM), and PICT 2016-0481(to APC), Sepkoski Grant 2016 (to APC), and CONICET to FAG, AHM, and APC.