The appendicular skeleton of the dwarf macronarian sauropod Europasaurus holgeri from the Late Jurassic of Germany and a re-evaluation of its systematic affinities

Abstract

The Late Jurassic was a period of great diversity for sauropod dinosaurs, with different lineages of Neosauropoda flourishing, including several camarasauromorph taxa. Efforts made in recent years have resulted in a great increase in our current knowledge of basal camarasauromorph evolution, including both the detailed description of new and previously poorly known sauropods and expanded phylogenetic analyses. Although most recent phylogenies converge in their results on early camarasauromorph diversification, the phylogenetic position of Europasaurus, from the Late Jurassic of Germany, remains controversial despite the completeness of the material representing this species. Although Europasaurus was recovered as a relatively basal camarasauromorph in all phylogenetic analyses to date, some of them retrieved this taxon in a slightly more derived position, among basal brachiosaurids. Europasaurus is not only one of the most complete camarasauromorphs but also the first unequivocal dwarf that evolved through paedomorphosis, retaining several plesiomorphic characters, especially in the cranium. Cranial and axial material of Europasaurus has been described in detail but the appendicular skeleton has not. The current paper rectifies this by providing detailed descriptions and illustrations of its appendicular skeleton. In addition, an extensive re-evaluation of the systematic position of Europasaurus was done based on the three most substantial data sets published in recent years. These analyses resolved Europasaurus as a basal camarasauromorph in all cases, but brachiosaurid affinities remain plausible, especially considering the heterochronic evolution of the taxon.

Keywords:

• Macronaria
• Camarasauromorpha
• dimorphism
• dwarfism
• Late Jurassic

Acknowledgements

We would like to dedicate this paper to the managing director of the Rohstoffbetriebe Oker, Fabian von Pupka, who sadly passed away in 2018. Without him, the research in the Langenberg Quarry would not have been possible. The authors gratefully acknowledge the financial support provided by the Deutsche Forschungsgemeinschaft (DFG) for this research (Project RE 2874/1–1 and SA 469/33-1) and FONCyT (PICT 0668 and 1925 to JLC). This is contribution number 176 of the DFG Research Unit 533 ‘Biology of the Sauropod Dinosaurs: The Evolution of Gigantism’. Critical comments made by the reviewers, J. Whitlock and P. Mannion, greatly helped to improve the manuscript. L. Salgado is thanked for comments made on earlier versions of the manuscript, and A. Otero and D. Pol are thanked for discussion on sauropodomorph ontogenetic changes. We thank the editors, S. Maidment and P. Barret, for accurate revision of the manuscript. Without the participation of the following people, the Europasaurus project would not be possible: Benjamin Englich, Janna von Pupka and Oliver Wings. Special thanks to the staff and volunteers at the DFMMh lab for the ongoing preparation of the Europasaurus material over the past 19 years.

Supplemental data

Supplementary material for this article can be accessed here: https://doi.org/10.1080/14772019.2019.1683770.

Associate Editor: Susannah Maidment