New Patagonian Cretaceous theropod sheds light about the early radiation of Coelurosauria

Abstract

Abstract:Here we describe a new theropod, Bicentenaria argentina nov. gen. et nov. sp., from the early Late Cretaceous of Patagonia. It is represented by more than a hundred bones belonging to different sized individuals, which were buried together in disarticulation after little transportation. The available association of skeletal elements suggests a gregarious behaviour for Bicentenaria, an ethological trait also recorded among other theropod clades. Increasing documentation of monospecific assemblages of different groups of theropods suggests that a gregarious behaviour may have constituted the ancestral condition for Theropoda, at least. Bicentenaria characterizes for the surangular bone with a high dorsal margin and a prominent lateral shelf, a retroarticular process that is low, wide and spoon-shaped, and quadrate bone with its lateral condyle larger than the medial one. Phylogenetic analysis found the Chinese Tugulusaurus and the Patagonian Bicentenaria as successive sister taxa of all other coelurosaurs, thus revealing the importance of the new taxon in the understanding of the early diversification of Coelurosauria. In particular, Bicentenaria amplifies the array of basal coelurosaurs that inhabited Gondwana during the Cretaceous, also including compsognathids, Aniksosaurus and Santanaraptor. Although still restricted to a handful of forms, available information indicates that Gondwana was a cradle for the evolution of different lineages of basal coelurosaurs, different from those documented in Upper Cretaceous beds in the northern landmasses. Analysis of body size distribution in averostran theropods results in the identification of two main episodes of drastic size reduction in the evolutionary history of Coelurosauria: one occurred at the initial radiation of the group (as represented by Bicentenaria, Zuolong, Tugulusaurus, compsognathids, and Aniksosaurus), and a second episode occurred at the early diverification of Paraves or avialans. Reduction in body size may have allowed adult coelurosaurians to exploit ecological niches not occupied before by larger basal averostrans.Key words: Coelurosauria, gregarism, body size reduction, Cretaceous, South America.Resumen: Nuevo terópodo del Cretácico de Patagonia brinda nuevas evidencias acerca de la radiación temprana de Coelurosauria. En la presente contribución se describe el nuevo terópodo Bicentenaria argentina nov. gen. et nov. sp., del Cretácico Tardío temprano de Patagonia. El nuevo taxón se encuentra representado por más de una centena de huesos pertenecientes a individuos de diferentes tamaños, los cuales fueron enterrados todos juntos en desarticulación, luego de un leve transporte. La asociación disponible de materiales sugiere hábitos gregarios para Bicentenaria, un rasgo etológico también registrado en otros clados de terópodos. La documentación recurrente de asociaciones monoespecíficas de diferentes grupos de terópodos sugiere que los hábitos gregarios pudieron haber constituido la condición ancestral para Theropoda. Bicentenaria se caract...

The Behavioral Implications of a Multi-Individual Bonebed of a Small Theropod Dinosaur

“…The femora (Figure 4A–B), despite having abraded articular ends, are robust and relatively short compared to those of most coelurosaurians, which are gracile and elongate [12], [21] (Table 1). Although of similar anatomies, the femora can be separated into two morphs based on metrics of the shafts, fourth trochanters, and fossae for the insertion of the Mm.…”

“…However, recent discoveries and descriptions of theropods with bones similar in proportions to Aniksosaurus [21], [22], [23], [24] suggested different lengths and lighter body weights. Using those comparisons, we suggest a total body length between 2–3 m and a body mass between 35–45 kg.…”

“…In South America, body fossil evidence for gregariousness in non-avian theropods is limited to Mapusaurus roseae [38], [39] and probably Bicentenaria argentina [21] (see below). However, the South American footprint record of non-avian theropods, particularly in Chile and Peru [11], suggests gregariousness.…”

Ordenamiento y caracterización faunística del Cretácico Superior del Grupo Chubut, Cuenca del Golfo San Jorge, Argentina

“…Las comparaciones efectuadas por estos autores están coherentemente enfocadas en formas no pertenecientes al Cretácico Superior, como Sinosauropteryx del Jurásico Superior o Cretácico Inferior de China (Currie & Chen, 2001); Nqwebasaurus thwasi del BerriasianoValanginiano de Sudáfrica (de Klerk et al, 2000); Sinraptor heping del Jurásico Superior de China (Currie & Zhao, 1993) y Allosaurus, Ornitholestes hermanni y Tanycolagreus topwilsoni estos tres últimos del Jurásico Superior de Estados Unidos (Osborn, 1903;Gilmore, 1920;Carpenter et al, 2005). Novas et al (2012), dieron a conocer un nuevo celurosaurio basal de la Formación Candeleros, Bicentenaria argentina. Este pequeño dinosaurio terópodo representaría otro de los linajes basales de celurosaurios que habitaron Patagonia durante el Cenomaniano.…”

“…Este pequeño dinosaurio terópodo representaría otro de los linajes basales de celurosaurios que habitaron Patagonia durante el Cenomaniano. Asimismo, basados en distintas evidencias, Bicentenaria, al igual que Aniksosaurus, podría haber tenido un comportamiento gregario (Novas et al, 2012;Ibiricu et al, 2013b). Esto apoyaría que este tipo de comportamiento está presente tempranamente en la evolución de Coelurosauria.…”