Ruyangosaurus

Classification

The describers of Ruyangosaurus assigned it to Andesauridae. However, Andesauridae is not monophyletic and, as such, is no longer used.

Comprehensive phylogenetic analyses of Titanosauriformes conducted by Philip Mannion and colleagues in 2013 found Ruyangosaurus to be in a polytomy with Andesaurus and other basal titanosaurs and near-titanosaur somphospondyls, supporting the original description's assertion of phylogenetic proximity of it and Andesaurus, though not the precise taxonomic assignment, with further modifications of the dataset resolving similar conclusions. However, not all phylogenetic analyses have supported its position as a somphospondyl. A phylogenetic dataset following the description of additional material for Ruyangosaurus to be a non-titanosauriform macronarian, closely related to Yunmenglong.

The phylogenetic analysis of Mannion et al. in 2019 incorporated these updated discoveries into their earlier analysis, along with additional new knowledge for other mid-Cretaceous Asian taxa considered close to Titanosauria. They found Ruyangosaurus to either be close to Andesaurus as a basal titanosaur when all characters were considered equally important, or in a large clade of early titanosaurs potentially given the name Euhelopodidae related to taxa like Yongjinglong and Huanghetitan ruyangensis. Two trees of the results are shown below, equal weighting displaying the results of basal titanosauria, and relationships within Euhelopodidae of extended-implied weighting with a mild down-weighting of highly variable characters (k=9).

Habitat

Ruyangosaurus shared its habitat with Xianshanosaurus, "Huanghetitan" ruyangensis, Yunmenglong, Luoyanggia, and Zhongyuansaurus. The horizon of Ruyangosaurus was originally described as being of "early Late Cretaceous" age, but recent work has assigned it an Aptian-Albian Age based on fieldwork and analysis of invertebrate and microfossil assemblages.