Tuesday, March 29, 2016

[Paleontology • 2016] Viavenator exxoni • A New Brachyrostran with Hypertrophied Axial Structures reveals An Unexpected Radiation of Latest Cretaceous Abelisaurids

Viavenator exxoni 
Filippi, Méndez, Juárez Valieri & Garrido, 2016 

A well preserved skeleton of a new abelisaurid is reported here. The holotype of Viavenator exxoni was found in the outcrops of the Bajo de la Carpa Formation (Santonian, Upper Cretaceous), northwestern Patagonia, Argentina. This new taxon belongs to the South American clade of abelisaurids, the brachyrostrans. The current phylogenetic analysis places it as the basalmost member of a new clade of derived brachyrostrans, named Furileusauria, characterized by distinctive cranial, axial and appendicular anatomical features. The Santonian age of Viavenator allows filling the stratigraphic gap exhibited between the basal brachyrostrans of Cenomanian–Turonian age, and the derived forms from the Campanian-Maastrichtian. The evolution of abelisaurids during the Late Cretaceous, faunal replacements, and the adaptive radiation that occurred during that period of time in South America are discussed.

Keywords: Abelisauridae; Brachyrostra; Furileusaira; Bajo de la Carpa; Upper Cretaceous; Neuquén Basin

Systematic paleontology

Theropoda Marsh, 1881
Ceratosauria Marsh, 1884

Abelisauridae Bonaparte & Novas, 1985
Brachyrostra Canale et al., 2009

Furileusauria clade nov.

Derivation of name. From Mapudungun language ‘Furileu’ stiff back, and Greek language ‘sauria’ lizard, in reference to the extreme level of stiffness in their axial skeletons.

Definition. The most inclusive clade containing to Carnotaurus sastrei but not Ilokelesia aguadagrandensis, Skorpiovenator bustingoryi or Majungasaurus crenatissimus.

Diagnosis. Furileusauria differs from all other brachyrostrans and other abelisaurids in the (1) presence of a tip in the middle area of the posterior surface of the ventral process of the postorbital, (2) presence of a knob followed by a deep notch in the postorbital-squamosal contact, (3) absence of fenestra between the frontal, postorbital and lacrimal, (4) anterior projection of the distal end of cervical epiphophyses, (5) posterior margin of the postzygapophyses at level with the intervertebral articulation in dorsal vertebrae, (6) crescent-shaped morphology of the distal tip of the transverse processes in anterior and middle caudal vertebrae, (7) transverse processes of anterior caudal vertebrae distally expanded and only anteriorly projected, (8) convex external margin of the transverse processes in the anterior caudals, (9) and cnemial crest of the tibia with a downturned process.

Included species. Viavenator exxoni, Carnotaurus sastrei, Abelisaurus comahuensis, Aucasaurus garridoi, Quilmesaurus curriei, Pycnonemosaurus nevesi.

Viavenator exxoni gen. et sp. nov.

Derivation of name. From latin ‘Via’ road, and ‘venator’ hunter, meaning the hunter of the road, ‘exxoni’ is in recognition of Exxonmobil's commitment to the preservation of paleontological heritage of the La Invernada area, Rincón de los Sauces, Neuquén, Patagonia Argentina.

Holotype. MAU-Pv-LI-530. 

Type locality. La Invernada area ( Fig. 1), located 50 km southwest from the Rincón de los Sauces city, Neuquén province, Patagonia, Argentina.

Stratigraphic horizon. Bajo de la Carpa Formation, Río Colorado Subgroup, Neuquén Group of the Neuquén basin. Santonian, Upper Cretaceous. The continental deposits of this lithostratigraphic unit have provided scant evidence relative to theropod dinosaurs. Small-sized forms include the noasaurid Velocisaurus unicus and the alvarezsaurids Alvarezsaurus calvoi and Achillesaurus manazonnei ( Bonaparte, 1991a and Martinelli and Vera, 2007). Mid and big sized theropods include a tetanuran possibly related to Carcharodontosauridae or Megaraptora (Porfiri et al., 2008) and indeterminate abelisaurid materials previously referred as Carnotaurines ( Ezcurra and Méndez, 2009 and Porfiri and Calvo, 2006), some of these found in the La Invernada area (see below).

Concluding remarks

In the present paper, we describe a new abelisaurid theropod from the Santonian of Patagonia, Argentina. The new form is here named Viavenator exxoni gen. et sp. nov., and possesses, among other characteristics, hypertrophied structures in the presacral axial skeleton.

Based in our phylogenetic analysis, Viavenator is found as a transitional brachyrostran, as the oldest member of a late radiation clade of the South American forms, named Furileusauria, and includes all the currently known abelisaurid taxa of this continent found in Santonian to Maastrichtian strata. The assemblages are found in a more complex biogeographic scenario with a division among European and Indo-Malagasy majungasaurines , with possible basal brachyrostrans in India and Madagascar.

Here we interpret that the furileusarians are supporting evidence of a late radiation of brachyrostran abelisaurids that fit with a faunal replacement that happened during the Turonian in South America, and is concordant with other dinosaur clades as the carcharodontosaurians, rebbachisaurids and derived lithostrotians.

Filippi, LS, Méndez, AH, Juárez Valieri, R. & Garrido, AC. 2016. A New Brachyrostran with Hypertrophied Axial Structures reveals An Unexpected Radiation of Latest Cretaceous Abelisaurids. Creataceous Research. 61:209-219.   DOI:  10.1016/j.cretres.2015.12.018

El MAU ya tiene su primer dinosaurio terópodo
Ya se encuentra publicado en versión online, en la revista Cretaceous Research, el trabajo sobre este dinosaurio carnívoro, un nuevo abelisaurio, que proviene de La Invernada de rocas de la Formación Bajo de la Carpa. La excelente preservación y la significativa información que aportó el ejemplar resultaron relevantes para avanzar en el conocimiento de este grupo de terópodos, los abelisaurios. Viavenator ("cazador del camino") exxoni gen. et sp. nov. es el primero dado a conocer de una serie de ejemplares que han sido recuperados en la zona de La Invernada gracias al enorme apoyo de la empresa Exxonmobil. 
Desde la Dirección del MAU se espera a futuro, poder llevar a delante una presentación formal del nuevo dinosaurio.

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