Amargatitanis macni, Apesteguia, 2007

D, Michael D. & Emic, 2012, The early evolution of titanosauriform sauropod dinosaurs, Zoological Journal of the Linnean Society 166 (3), pp. 624-671 : 646

AMARGATITANIS MACNI ( APESTEGUÍA, 2007)

Apesteguía (2007) named Amargatitanis on the basis of fragmentary material (caudal vertebrae, scapula, femur, astragalus; MACN PV N52, 53, 34) from Neuquén, Argentina. Material referred to Amargatitanis was thought to come from the Kimmeridgian Pichi Pecún Leufú Formation when it was discovered, but the preservational style suggests that it is from the Barremian La Amarga Formation ( Apesteguía, 2007). Amargatitanis was described as a derived titanosaur, and would constitute one of the oldest known members of that clade. However, although Apesteguía (2007) reported that the material was associated, field notebooks of J. Bonaparte indicate that the material was collected over several hundred metres of outcrop – for example, the femur and astragalus were collected over 400 m from the caudal vertebrae (pers. observ., 2009; S. Apesteguía, pers. comm.).

Although presented as a titanosaur ( Apesteguía, 2007), none of the material referred to Amargatitanis bears synapomorphies of Titanosauria according to the analysis presented herein. Several of the features cited in support of somphospondylan or titanosaur affinities by Apesteguía (2007) are instead the result of breakage. These include the medially bevelled scapular glenoid, straight scapular blade, and bevelled femoral condyles (i.e. these features are all broken; M. D. D’Emic, pers. observ., 2009). Likewise, fragmentary teeth from the La Amarga region cannot be ascribed to titanosaurs. A ‘dendritical enamel pattern’ and ‘homogenous slenderness’ were features used to refer these teeth to titanosaurs ( Apesteguía, 2007: 539), but titanosaur enamel is not diagnostic ( Upchurch et al., 2004), and diplodocoids and some basal titanosauriforms also have similarly slender and similarly shaped teeth ( Chure et al., 2010). The purported titanosaur teeth could pertain to non-titanosaurs similar to Abdyosaurus or Ligabuesaurus based on their shape ( Apesteguía, 2007: fig. 4). Some of the other material referred to Amargatitanis may pertain to diplodocoids on the basis of complex neural arch lamination in the anterior caudal vertebrae (pers. observ., 2009). The titanosaur affinities of material referred to Amargatitanis cannot be substantiated at present, and its validity is questionable.