Osteology of Dashanpusaurus dongi (Sauropoda: Macronaria) and new evolutionary evidence from Middle Jurassic Chinese sauropods

Abstract

The Middle Jurassic lower Shaximiao Formation in Sichuan Province of south-western China has yielded a diverse terrestrial vertebrate fauna dominated by sauropod dinosaurs. However, many of these sauropods lack detailed descriptions or explicit phylogenetic diagnoses. Here, we present a comprehensive redescription of Dashanpusaurus dongi, a species of sauropod found only in the lower Shaximiao Formation. We define the revised autapomorphies of the species as follows: neural canals are sub-square in anterior dorsal vertebrae; the presence of a thin accessory lamina that contacts the prezygodiapophyseal and paradiapophyseal laminae of the middle dorsals, forming an angle of 75° to the horizontal; and four ridges on the anterodistal edge of the humerus. Often considered part of the epipophyseal-prezygapophyseal lamina, a strut invades the spinodiapophyseal fossa in the cervical and anterior dorsal vertebrae. Anatomical comparisons indicate that this feature was widespread among early-diverging Middle Jurassic eusauropod lineages. This comparative anatomical data provides an opportunity to revisit the phylogenetic position of Dashanpusaurus and the relationships of the neosauropod clade. Recovered as a macronarian, a better understanding of Dashanpusaurus dongi will allow for clarification of the origin, early evolution, and palaeogeographical distribution of neosauropods. This study also suggests that the diversity and dispersity of the neosauropod clade occurred much earlier than previously realized.

Keywords:

• Sauropoda
• Neosauropoda
• Macronaria
• Dashanpusaurus dongi
• Middle Jurassic
• lower Shaximiao Formation

Acknowledgements

For their hospitality and access to the materials in their care, we thank Liu Yu, Shen Xi and Zhou Xiao-Mei (ZDM) for their generous help during a research trip to the Zigong Dinosaur Museum, Sichuan, China. We are grateful to Paul M. Barrett for suggestions that improved the earlier and final versions of this manuscript. Thoughtful reviews by Philip D. Mannion, Andrew J. Moore and the editor significantly improved the manuscript. This work was supported by grants from the Strategic Priority Research Programme of the Chinese Academy of Sciences [Grant No. XDB26000000], the National Natural Science Foundation of China [Grant No. 42288201, 42102018, and 41872021], and the China Geological Survey [Grant No. DD20221649].

Supplemental material

Supplemental material for this article can be accessed here: https://dx.doi.org/10.1080/14772019.2022.2132886.

Associate Editor: Paul Barrett