Tuesday, 13 August 2013

An Abelisauroid from the Late Cretaceous of Brazil.

The Albelisauroids were a group of Theropod Dinosaurs that appeared in the Middle Cretaceous, and underwent a major diversification in the Cretaceous. They were restricted to the southern continent of Gondwana, which by the Cretaceous had separated from the supercontinent of Pangea and started to break up into the continents of today's Southern Hemisphere; Albelisauroids are known from Africa, Madagascar, India and South America. Albelisauroids were noted for having short, but tall and often ornamented skulls, as well as often having greatly reduced forelimbs.

In a paper published in the journal Revista Mexicana de Ciencias Geológicas on 4 March 2013, Elaine Machado of the Laboratório de Sistemática e Tafonomia de Vertebrados Fósseis at the Departamento de Geologia e Paleontologia at the Museu Nacional and Universidade Federal do Rio de JaneiroDiogenes de Campos of the Museu de Ciências da Terra at the Departamento Nacional de Produção Mineral do Brasil, Jorge Calvo of the Centro Paleontológico Lago Barreales at the Universidad Nacional del Comahue and Alexander Kellner also of the Laboratório de Sistemática e Tafonomia de Vertebrados Fósseis discuss a new Albelisauroid specimen from the Maastrichtian (end Cretaceous) Marília Formation near Peirópolis in Brazil.

The specimen is described from a single right tibia, 395 mm in length, though considered distinctive enough that Machado et al. do not consider that it belonged to any previously described species. However due to the limited nature of the material, the specimen is not formally described as a new species, but rather referred to as the 'Cambará Theropod'.

Right tibia of the Cambará Theropod. (a) Anterior view showing the torsion presented in relation to the proximal and distal condyles; (b) posterior view showing the two asymmetrical condyles and the surrounding muscle attachment scars; (c) medial view, showing muscle scars on the proximal epiphysis, and muscle scars in proximal and distal portions; and (d) lateral view; note the cnemial crest is elevated above the proximal articulation. Abbreviations: cnc - cnemial crest, dep - depression, gr –groove, tfap - tibial facet for ascending process of astragalus, tfas - tibial facet for astragalus, fc - fibular crest, ff - fibular facet, lcon - lateral condyle, lm - lateral malleolus, mcon -medial condyle, mm - medial malleolus, mus - muscle scar. Scale bar is 100 mm. Machado et al. (2013).

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