Friday, June 23, 2017

[Paleontology • 2017] The Chinese Colossus: An Evaluation of the Phylogeny of ​Ruyangosaurus giganteus​ and Its Implications for Titanosaur Evolution


Skeletal and life restorations of the Ruyangosaurus giganteus holotype by Nima Sassani.
Osteoderms hypothesized based on Vidal, Ortega, and Sanz (2014). Beige elements are based on undescribed material likely referable to the holotype specimen. Scale bar equals 4m.

Abstract

For many years the precise taxonomy of Titanosauria has been a puzzle, and even today only certain segments of this vast clade are well-understood. The phylogenetic positions of many titanosaurs are murky, though specimens often still await rigorous analysis. One of the largest examples is the massive Chinese titanosaur Ruyangosaurus giganteus – though largely incomplete, the holotype is distinct enough to indicate strong phylogenetic affinities with a specific subgroup of titanosaurs. A review of previous literature on Ruyangosaurus, referred tentatively to Andesauridae, shows that this classification is based on three weak, non-diagnostic characters. Ruyangosaurus differs from taxa traditionally included in Andesauridae in at least 20 characters of the torso, femur, and tibia. Several plesiomorphies of Ruyangosaurus are extremely rare in titanosauria except for the clade Lognkosauria and its close relatives. The vertebra initially described as a posterior cervical is most likely an anterior dorsal, with a strong resemblance to that of Puertasaurus. The posterior dorsal of Ruyangosaurus shares synapomorphies with Mendozasaurus and Dreadnoughtus. The femur clusters close to the femora of Malawisaurus, Traukutitan, and Pitekunsaurus. Ruyangosaurus is here recovered as a lognkosaurian, with significant implications for the distribution and evolution of that group and the paleobiology of Mid-Cretaceous China.

Fig. 15. Skeletal and life restorations of the Ruyangosaurus giganteus holotype by Nima Sassani. Osteoderms hypothesized based on Vidal, Ortega, and Sanz (2014). Beige elements are based on undescribed material likely referable to the holotype specimen. Scale bar equals 4m.

CONCLUSION: 
Ruyangosaurus giganteus represents a new and unusual radiation of Lognkosauria in Asia in the early part of the Late cretaceous period, coinciding with a time of Africa’s final separation from South America and gradual collision with Asia. Its unique morphology implies a close relationship to Puertasaurus, and it is possible it may form a subclade within Lognkosauria with NotocolossusPitekunsaurus, and Puertasaurus, with MendozasaurusDreadnoughtus and Futalognkosaurus forming another sub-clade. However, Ruyangosaurus differs from all other lognkosaurs and the rest of titanosauria in having neural fossae separated from the neural canal by laminae, in having a strange quartet of nearly flat “spider laminae” on the posterior neural arch of the posterior dorsal, and in having the intraprezygapophyseal lamina located far higher on the neural arch in the anterior dorsal. As there is a paucity of Ruyangosaurus material,diagnosis of many features is not possible, though it shows a particularly strong affinity with Puertasaurus in anterior dorsal morphology and with Lognkosauria and Lithostrotia in general asit lacks defined hypantra and hyposphenes. Based on the dorsal material, the Ruyangosaurus holotype is a very large sauropod, exceeding Futalognkosaurus and Dreadnoughtus in size.Based on the dimensions of the anterior dorsal, it likely also exceeded Notocolossus, though wasprobably smaller than Puertasaurus and the recently discovered titanosaur species in the MPEF collections still awaiting description. This newly excavated taxon from Argentina’s Chubut province is known from multiple specimens in an excellent state of preservation, which appearstrongly lognkosaurian in morphology, among which the largest femur appears to be roughly 2.6 m in length


Nima Sassani and Gunnar Tyler Bivens. 2017. The Chinese Colossus: An Evaluation of the Phylogeny of ​Ruyangosaurus giganteus​ and Its Implications for Titanosaur Evolution.   PeerJ Preprints. 5:e2988v1. DOI: 10.7287/peerj.preprints.2988v1




 

 Lü J, Xu L, Jia S, Zhang X, Zhang J, Yang L, You H and Ji Q. 2009. A New Gigantic Sauropod Dinosaur from the Cretaceous of Ruyang, Henan, China. Geological Bulletin of China. 28(1); 1-10.

Ruyangosaurus giganteus (Lü et al., 2009) ... Art by Zhao Chuang

No comments:

Post a Comment