New Titanosaur With Unusual Haemal Arches From The Upper Cretaceous Of Neuquén Province, Argentina

Abstract

The Neuquén Basin has yielded a highly diverse fauna of sauropod dinosaurs. This group includes diplodocoids (e.g., Salgado and Bonaparte, 1991; Salgado et al., 2004; Haluza et al., 2009) and titanosaurs (e.g., Lydekker, 1893; Calvo and Bonaparte, 1991; Bonaparte and Coria, 1993; Salgado and Azpilicueta, 2000; Apesteguía, 2004; González Riga, 2003; Filippi et al., 2011). The plentiful record of titanosaur sauropods in the Upper Cretaceous of northern Patagonia is mostly restricted to derived titanosaurs included in the Titanosauridae (=Lithostrotia sensu Upchurch et al., 2004). Derived titanosaurs were traditionally characterized by the possession of strongly procoelous anterior-middle caudal vertebrae. This feature was used as a diagnostic trait to differentiate them from basal forms of titanosaurs with amphiplatyan or am- phicoelous caudal vertebrae (Salgado et al., 1997). However recent discoveries have demonstrated that a great variation exists throughout the titanosaurian caudal series (Salgado and Calvo, 1993; Wilson et al., 1999; Calvo and González Riga, 2003; González Riga et al., 2009). In this sense, procoely appears to be non-continuous along the tail, implying a very different morphological scenario. In this paper we report a series of sauropod caudal vertebrae collected from the upper levels of the Candeleros Formation (Neuquén Group) near Villa El Chocón, Neuquén Province, Argentina. The materials, previously referred tentatively to Andesaurus (Otero et al., 2006), include a discontinuous series of mid and mid-posterior caudal vertebrae,most of them including their haemal arches. The latter elements present an unusual morphology hitherto not reported in other sauropod dinosaurs.