Phylogenetic analysis of gondwanan basal eusauropods from the early-middle Jurassic of Patagonia, Argentina

Abstract

Gondwanan Jurassic non-neosauropod eusauropods are key for the understanding of sauropod evolution, although their phylogenetic interrelationships remain poorly understood. However, following the revision of the holotype of a key taxon from the early Middle Jurassic Cañadón Asfalto Formation Patagonia, Argentina, Patagosaurus fariasi, the phylogenetic affinities need to be tested with new osteological information gathered during the redescription of the holotype of Patagosaurus. A new phylogeny presented here shows a close affiliation of Patagosaurus with Cetiosaurus from the Middle Jurassic of the UK. The close relationship of Patagosaurus with Barapasaurus, often found in previous phylogenies, was not recovered here. Instead, Patagosaurus is retrieved as more derived than most Early and Middle Jurassic sauropods, although more basal to Mamenchisaurus, Omeisaurus, turiasaurians, and neosauropods. Another sauropod taxon found together with Patagosaurus, Volkheimeria, is retrieved several nodes more basal than the former, which shows, together with evidence of several other sauropod taxa in the Cañadón Asfalto Formation, that a high evolutionary diversity existed in Southwest Gondwana in the early Middle Jurassic, a pattern which is also seen in fossil groups other than sauropods (e.g., theropods).