REAPPRAISAL OF THE EARLY CRETACEOUS SAUROPOD DINOSAUR AMARGATITANIS MACNI (APESTEGUÍA, 2007), FROM NORTHWESTERN PATAGONIA, ARGENTINA

GALLINA, P.A.

Buenos Aires

Jornada; Jornadas Argentinas de Paleontología de Vertebrados; 2016

Museo Argentino de Ciencias Naturales

Amargatitanis macni Apesteguía, 2007 was described as a purported titanosaur sauropod. However, this referral and even the systematic validity of the taxon were questioned. Here, all the available remains of the taxon are evaluated including a description of unpublished elements. The identity of the type material is discussed based on a first-hand examination of the specimens and evaluation of the original field notes as reliable evidence for bone association. The original holotype of Amargatitanis is a chimaera, as pointed out by previous authors. Herein a new, modified holotype for Amargatitanis is proposed. This analysis presents a revised diagnosis for Amargatitanis macni as a valid taxon. Several features observed on the modified type material revealed closer affinities to diplodocoids than macronarians. The presence of a fibular facet of the astragalus facing posterolaterally, and the absence of a lateral bulge in the femur, link Amargatitanis with Diplodocoidea. Additionally, the presence of a posterolateral projection on the distal condyle of the first metatarsal, and anterior caudal centra with procoelous/distoplatyan articular surfaces, are shared with other flagellicaudatans. The position of the highest point of the femoral head laterally shifted, above the main portion of shaft, and the anterior caudal transverse processes directed dorsally, also support affinities with dicraeosaurids. The inclusion of Amargatitanis macni in an updated phylogenetic analysis revealed the presence of a second species of the family Dicraeosauridae in the La Amarga Formation, suggesting that, at present, there is no record of titanosaur body fossils in Patagonia prior to Cenomanian times.