a ridge-like structure. Discovery and naming The holotype of Triunfosaurus, UFRJ-DG 498, was found in a sandstone layer of the Rio Piranhas Formation to the west of Paraíba State, Brazil. It consists of a partial skeleton including a series of three middle tail vertebrae (subsequently considered to be vertebrae from the front of the tail), three isolated chevrons, three isolated neural spines, and a right ischium. The fossils are part of the collection of the Universidade Federal do Rio de Janeiro. Based on correlation using pollen and co-occurrence of similar trackways, the Rio Piranhas Formation has been considered as a contemporary of the Sousa Formation, which extends from the Berriasian to the Valanginian, and possibly into the Hauterivian (correlating to the Rio da Serra and early Aratu faunal stages). Study of pollen found in the Rio Piranhas itself supports a Berriasian-Valanginian age, although the presence of Hauterivian deposits cannot be ruled out. The type and only species Triunfosaurus leonardii was named and described in 2017 by Ismar de Souza Carvalho, Leonardo Salgado, Rafael Matos Lindoso, Hermínio Ismael de Araújo-Júnior, Francisco Cézar Costa Nogueira and José Agnelo Soares. The generic name refers to the Triunfo Basin in Paraíba, while the specific name honours the paleontologist Giuseppe Leonardi. Classification Initial titanosaurian identification In 2017, Triunfosaurus was placed in the clade Titanosauria as defined by Wilson and Upchurch in 2003, which is supported by the articulations of its haemal arches having two distinct surfaces as in other titanosaurs. Initially, Triunfosaurus was found to be in a rather basal polytomy along with Mendozasaurus; this basal position is supported by the tail vertebrae having flattened back ends, instead of being convex in the procoelous configuration of derived lithostrotian titanosaurs. Additionally, the short shaft of the ischium - and indeed the proportions of the bone in general - are quite similar to that of the similarly basal Andesaurus. However, the straight vertical neural spines warrant a more derived position than either Andesaurus or Mendozasaurus, while the relative shortness of the haemal canal relative to the rest of the haemal arch distinguishes Triunfosaurus from Andesaurus and other titanosaurs. The topology recovered, based on the dataset of Carballido & Sander, is reproduced below. This topology is poorly supported, since forcing Triunfosaurus to nest outside of the Titanosauria would require only two additional evolutionary steps, and the support values obtained for the clades are also low. As the oldest