[D] Bicentenaria argentina [Su] [sG] [T]
Novas, Ezcurra, Agnolín, Pol & Ortíz 2012
Cretaceous Late Cenomanian
Saurischia Theropoda Tetanurae Coelurosauria
Candeleros Formation, Río Limay Subgroup, Neuquén Group, Río Negro Province, Argentina
Novas, F.E., Ezcurra, M.D., Agnolín, F.L., Pol, D. and Ortíz, R. (2012). New Patagonian Cretaceous theropod sheds light about the early radiation of Coelurosauria. Revista del Museo Argentino de Ciencias Naturales, nueva serie, 14: 57–81.
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 suggeststhat a gregarious behaviour may have constituted the ancestral condition for Theropoda, at least. Bicentenariam 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 andSantanaraptor. 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.
From bicentenary, due to the 200 years of the Revolution of May (25th May 1810), which lead to the first Argentinean autonomous government, thus constituting one of the most important chapters in the history of this South American country. Specific epithet honors Argentina, the country where the specimens were recovered.
MPCA 865, caudal half of skull in articulation with the lower jaws
MPCA 866, around 130 bones, including fragments of two articulated premaxillae with three pairs of teeth, an incomplete right maxilla with a single tooth, fragments of seventeen dorsal vertebrae, fourteen sacral vertebrae, twenty caudal vertebrae, fragments of two scapulae, caudodorsal corner of a right coracoid, proximal ends of three ulnae, distal end of radius, eight manual unguals, fragments of left ilium, proximal fragments of five pubic shafts, five incomplete femora, proximal thirds of two left tibiae and distal end of the right one, right astragalus, fragments of five metatarsals, fifteen non-ungual pedal phalanges, eight pedal unguals, and several isolated rib fragments.
Locality and horizon
Upper levels of the Candeleros Formation (Cenomanian, early Late Cretaceous; Leanza et al., 2004), Río Limay Subgroup, Neuquén Group. The fossiliferous locality is placed at the east shore of Ezequiel Ramos Mexía Reservoir, Río Negro Province, Northern Patagonia, Argentina. The rocks of the Candeleros Formation which yielded the remains of Bicentenaria argentina are made up by red medium sized sandstones and mudstones, with abundant dark-brownish paleosoils representing a fluvial environment under braided and meandering regimes, as well as in aeolian conditions (Leanza et al., 2004; Garrido, 2011).
Bicentenaria argentina was a smallsized theropod ca. 3 m long [estimated by extrapolating bone measurements from the reconstructed skeletons of Compsognathus and Tanycolagreus; Ostrom, 1978; Carpenter et al.,2005)] and ca. 40 kg of body mass [following formula from Seebacher (2001)]. Bicentenaria argentina is diagnosed on the following autapomorphies:premaxillary teeth with mesial denticles only at the base of the crown; quadratojugal with a rostral process two times longer than the dorsal process; quadrate with lateral condyle much larger than the medial one; surangular with a raised dorsal margin trapezoidal-shaped in lateral profile; retroarticular process dorsoventrally depressed, transversely wide, and spoon-shaped; humerus with proximal end craniocaudally flattened, and distal end bearing a deep fossa on its cranial surface; and manual unguals of external digits bearing proximal dorsal lips.