Caieiria allocaudata gen. et sp. nov.

Etymology: The generic name derives from “Caieira”, the site where the type-specimen was unearthed. The specific name employs the word allos (Greek for strange) and cauda (Latin for tail), in reference to the unique anatomy of the animal’ s tail vertebrae.

Holotype: MCT 1719-R, 10 anterior to middle caudal vertebrae.

Type-locality and horizon: MCT 1719-R was collected in the site known as “Caieira”, or “Quarry 1”, Serra do Veadinho area, near Peirópolis, Minas Gerais, Brazil (Campos & Kellner, 1999). The bearing sandstones belong to the Serra da Galga Formation, Bauru Group (Martinelli et al., 2019; Soares et al., 2020, 2021).

Diagnosis: Caieiria allocaudata can be distinguished from Baurutitan britoi, Uberabatitan ribeiroi, and Gondwanatitan faustoi by the presence of caudal vertebrae with robust and dorsoventrally expanded transverse processes, almost half the centrum height (modified from Campos et al., 2005), and anterior caudal vertebrae with a deep postzygapophyseal centrodiapophyseal fossa (newly proposed here).

For the first iteration we added the BR-262 specimens, plus the holotypes of Ba. britoi, T. pricei, and C. allocaudata to the matrix. This resulted in 1,620 most parsimonious trees (MPTs) of 1,504 steps. The strict consensus tree (Fig. 23B) shows Gondwanatitan faustoi, the BR-262 specimens, plus the holotypes of Ba. britoi and T. pricei, within a polytomy along with a clade including C. allocaudata and Bravasaurus arrierosorum. In the entire set of MPTs, four possible arrangements for this polytomy were found, as seen in Fig. 23C.

Caieira allocaudata and Br. arrierosorum form a minimal clade in all alternative arrangements, sister to either G. faustoi or to a clade congregating the other Serra da Galga Formation titanosaurs. Alternatively, G. faustoi was recovered either within or as sister-taxon to the specimens assigned here to Ba. britoi.

The second iteration was performed with the coding of the BR-262 specimens and the holotypes of Ba. britoi and T. pricei combined. This resulted in 1,500 MPTs of 1,502 steps. The strict consensus tree (Fig. 23A) shows Ba. britoi in a polytomy with G. faustoi and a clade including C. allocaudata and Br. arrierosorum. The clade congregating these four taxa is supported by a single synapomorphy: middle to posterior trunk vertebrae with pneumatic fossae located on the dorsal margin of the centra (Ch. 189), as seen in Ba. britoi and Br. arrierosorum. The clade composed of C. allocaudata and Br. arrierosorum is also united by a single synapomorphy: posteriormost anterior and middle caudal vertebrae with vertical neural spines (Ch. 257).

With additional specimens (MCT 1488-R and BR-262), the phylogenetic results confirm the position of Ba. britoi as an Aeolosaurini, as proposed by Hechenleitner et al. (2020) and Silva Junior et al. (2022). Previously, Ba. britoi was recovered either as a Lithostrostia indet. (Carballido et al., 2017; Filippi, Salgado & Garrido, 2019) or as a Saltasaurinae-like taxon (e.g., Santucci & Arruda-Campos, 2011; França et al., 2016; Gorscak et al., 2017; Carballido et al., 2020). As for the now defunct T. pricei, besides its recent association to Aeolosaurini (Hechenleitner et al., 2020; Silva Junior et al., 2022), it has been previously recovered in disparate positions within Lithostrotia (e.g., Bandeira et al., 2016; Martínez et al., 2016; Gorscak & O’ Connor, 2019).

The affinity of C. allocaudata also to Aeolosaurini reinforces that this clade dominated the Late Cretaceous sauropod fauna of the Bauru Basin. This is the case not only of the Serra da Galga Formation, with Ba. britoi, U. ribeiroi, and C. allocaudata, but also of the Adamantina Formation, with Ar. maximus and G. faustoi (Santucci & Arruda-Campos, 2011; Silva Junior et al., 2022).