Abstract
Partial remains of a titanosaur sauropod collected in the Tolar Formation (Upper Cretaceous) at the Atacama Desert (Antofagasta Region), northern Chile, is described, and a new species, Atacamatitan chilensis gen. et sp. nov., is erected. The material consists mainly of dorsal and caudal vertebrae, part of a humerus and a femur. The presence of a titanosaur confirms the Cretaceous age for the outcrops of red sandstone of the Tolar Formation whose age was previously uncertain, ranging from the Upper Cretaceous to the Paleocene. The new specimen represents the most complete dinosaur reported for this region and one of the most complete titanosaur known from Chile and the pacific margin of South America so far.
Highlights
The record of continental fossil vertebrates in Mesozoic deposits of Chile is very rare
In order to prospect for continental Mesozoic tetrapod fossils in Chile, contacts between Chilean and Brazilian researchers were established in 1998 and a preliminary expedition during February 2000 was organized by the Museo Nacional de Historia Natural (San-Proceedings of the Third Gondwanan Dinosaur Symposium Correspondence to: Alexander Wilhelm Armin Kellner E-mail: kellner@mn.ufrj.br tiago) and the Museu Nacional/UFRJ (Rio de Janeiro) to the Antofagasta region
Comparing the dorsal vertebrae of Atacamatitan chilensis with other titanosaurids, they differ from Trigonosaurus, Gondwanatitan, Uberabatitan and Saltasaurus by the strongly concave ventral margin of the centrum, for all in SGO-PV-961a (Powell 1992, Kellner and Azevedo 1999, Campos et al 2005, Salgado and Carvalho 2008)
Summary
The record of continental fossil vertebrates in Mesozoic deposits of Chile is very rare. Comparing the dorsal vertebrae of Atacamatitan chilensis with other titanosaurids, they differ from Trigonosaurus, Gondwanatitan, Uberabatitan and Saltasaurus by the strongly concave ventral margin of the centrum, for all in SGO-PV-961a (Powell 1992, Kellner and Azevedo 1999, Campos et al 2005, Salgado and Carvalho 2008). In this respect, there are similarities with Muyelensaurus, Mendozasaurus and, to some extent, with Opisthocoelicaudia (Salgado et al 1997, González Riga 2003, Calvo et al 2007b). The preserved posterior caudal vertebrae of Gondwanatitan show a straighter ventral margin (Kellner and Azevedo 1999), contrasting with the concave condition observed in Atacamatitan This Brazilian titanosaurid has a broader and more inclined neural spine. The posterior surface of the distal end of the femur shows a depression that gently separates the medial and lateral condyles
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