Monday, April 2, 2018

[Paleontology • 2018] Tratayenia rosalesi • A New Megaraptoran Theropod Dinosaur from the Upper Cretaceous Bajo de la Carpa Formation of northwestern Patagonia

Tratayenia rosalesi 
Porfiri, Juárez Valieri, Santos & Lamanna, 2018

  DOI: 10.1016/j.cretres.2018.03.014 
Illustration: Andrew McAfee

We describe Tratayenia rosalesi gen. et sp. nov., a new megaraptoran theropod dinosaur from the Upper Cretaceous of Patagonia, Argentina. The holotype consists of a well-preserved, mostly articulated series of dorsal and sacral vertebrae, two partial dorsal ribs, much of the right ilium, and pubis and ischium fragments. It was found in a horizon of the Upper Cretaceous (Santonian) Bajo de la Carpa Formation of the Neuquén Group in the Neuquén Basin exposed near the town of Añelo in Neuquén Province of northwestern Patagonia. Phylogenetic analysis recovers Tratayenia within the Gondwanan megaraptoran subclade Megaraptoridae. The new taxon exhibits similarities to other megaraptorids such as Aerosteon riocoloradensis, Megaraptor namunhuaiquii, and Murusraptor barrosaensis, but also presents differences in the architecture of the dorsal and sacral vertebrae and the morphology of the ilium. Tratayenia is the first megaraptoran that unequivocally preserves the complete sequence of sacral vertebrae, thereby increasing knowledge of the osteology of the clade. Moreover, depending on the chronostratigraphic ages of the stratigraphically controversial megaraptorids Aerosteon and Orkoraptor burkei, as well as the phylogenetic affinities of several fragmentary specimens, the new theropod may be the geologically youngest megaraptorid or megaraptoran yet discovered. Tratayenia is also the largest-bodied carnivorous tetrapod named from the Bajo de la Carpa Formation, reinforcing the hypothesis that megaraptorids were apex predators in southern South America from the Turonian through the Santonian or early Campanian, following the extinction of carcharodontosaurids.

Keywords: Theropoda; Megaraptora; Megaraptoridae; Bajo de la Carpa Formation; Upper Cretaceous; Patagonia; Argentina

Figure 3. Preserved dorsal vertebrae and sacrum of  Tratayenia rosalesi gen. et sp. nov. (MUCP v1162). A, left lateral view. B, right lateral view.

Figure 2. Tentatively reconstructed body silhouette of  Tratayenia rosalesi gen. et sp. nov. showing the bones preserved in the holotype (MUCP v1162). Body regions not preserved in Tratayenia are based primarily on corresponding elements of the following megaraptorid species: cranium (Megaraptor namunhuaiquii, Murusraptor barrosaensis), mandible (Australovenator wintonensis, M. barrosaensis), postcranial axial skeleton (Aerosteon riocoloradensis, M. namunhuaiquii), appendicular skeleton (A. riocoloradensis, A. wintonensis, M. namunhuaiquii). Scale bar equals 1 m.

Systematic paleontology
 Dinosauria Owen, 1842
 Theropoda Marsh, 1881
 Tetanurae Gauthier, 1986

 Megaraptora Benson, Carrano, and Brusatte, 2010
 Megaraptoridae Novas, Agnolín, Ezcurra, Porfiri, and Canale, 2013

 Tratayenia rosalesi gen. et sp. nov. 

Etymology. Genus name for Tratayén, the locality where the holotype was collected; species name in honor of Diego Rosales, the discoverer of the specimen. 


Tratayenia rosalesi is a new taxon of megaraptoran theropod, the first to be described from the Santonian Bajo de la Carpa Formation of the Neuquén Group. Its discovery constitutes a previously unreported stratigraphic occurrence in the megaraptorid fossil record of northern Patagonia. The elevated pneumaticity and morphological resemblance of the axial and pelvic elements of Tratayenia to those of the megaraptorids Aerosteon riocoloradensis and Murusraptor barrosaensis suggests 851 particularly close relationships between these three taxa. Nevertheless, Tratayenia also exhibits a number of unique morphologies that justify the erection of a new taxon. The holotype is the first megaraptoran specimen to preserve a nearly complete sequence of middle and posterior dorsal vertebrae and the complete sacrum, which augments knowledge of serial variation in this area of the axial skeleton. Tratayenia rosalesi is the largest carnivorous taxon known from the Bajo de la Carpa Formation, and, like other Patagonian megaraptorids, was likely the apex predator in its paleoecosystem. 

Juan D. Porfiri, Rubén D. Juárez Valieri, Domenica D.D. Santos and Matthew C. Lamanna. 2018. A New Megaraptoran Theropod Dinosaur from the Upper Cretaceous Bajo de la Carpa Formation of northwestern Patagonia. Cretaceous Research. In Press.  DOI: 10.1016/j.cretres.2018.03.014


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