The past, present and future of Jensen's “Big Three” sauropods
- Published
- Accepted
- Subject Areas
- Evolutionary Studies, Paleontology
- Keywords
- dinosaur, sauropod, Dry Mesa Quarry, Jim Jensen, Supersaurus, Ultrasaurus, Ultrasauros, Dystylosaurus, Barosaurus, scapulocoracoid
- Copyright
- © 2019 Taylor et al.
- Licence
- This is an open access article distributed under the terms of the Creative Commons Attribution License, which permits unrestricted use, distribution, reproduction and adaptation in any medium and for any purpose provided that it is properly attributed. For attribution, the original author(s), title, publication source (PeerJ Preprints) and either DOI or URL of the article must be cited.
- Cite this article
- 2019. The past, present and future of Jensen's “Big Three” sauropods. PeerJ Preprints 7:e27970v1 https://doi.org/10.7287/peerj.preprints.27970v1
Abstract
In the 1970s, Jim Jensen excavated multiple gigantic sauropod dinosaurs from Dry Mesa Quarry (DMQ), Colorado. In 1985, he formally named Supersaurus, Ultrasaurus (later Ultrasauros), and Dystylosaurus based on these specimens. Later, Brian Curtice and coauthors referred the holotype vertebrae of Ultrasauros and Dystylosaurus to Supersaurus, and the referred scapulocoracoid of Ultrasauros to Brachiosaurus.
In 2016, we determined that a large cervical vertebra referred to Supersaurus in fact belongs to Barosaurus. Either Supersaurus is synonymous with Barosaurus, or it is distinct but some Barosaurus material has been incorrectly referred. The holotype of Dystylosaurus, an anterior dorsal vertebra, cannot belong to Barosaurus due to its unsplit neural spine, but no shared apomorphies support its referral to Supersaurus and the convenient referral of all large diplodocid material from DMQ to Supersaurus is no longer supportable in light of the Barosaurus cervical.
Nomenclatural issues pertaining to Supersaurus must be resolved by reference to its holotype scapulocoracoid. Jensen assigned two scapulocoracoids to Supersaurus, but his vague descriptions, and pervasive confusion around published specimen numbers, make it uncertain which of the two is the type. The two elements have subtle differences and may not belong to the same animal. This is unfortunate, since Supersaurus is the most complete, phylogenetically informative, and nomenclaturally stable of the “Big Three” Dry Mesa sauropods — or at least it was until now.
Finally, while the scapulocoracoid referred to Ultrasauros is probably from a titanosauriform, its coracoid does not closely resemble that of the holotype of Brachiosaurus, nor its scapulae those of Giraffatitan. In summary, the DMQ material includes at least three giant sauropods: a titanosauriform that may not be Brachiosaurus, and two diplodocids: Barosaurus and Supersaurus – but the diagnosis of the latter is muddied both by possible confusion with Barosaurus, and by definite confusion regarding the holotype.
Author Comment
This is the abstract for our presentation at the 67th Symposium on Vertebrate Palaeontology and Comparative Anatomy (SVPCA), Isle of Wight, UK, 11th-13th September 2019. Mike Taylor presented the talk in the morning of Friday, September 13th. The slideshow presented on the Isle of Wight is attached as a supplementary file, and a video of the talk (recorded after the conference) can be found at https://www.youtube.com/watch?v=miGAdey4US0
Supplemental Information
Taylor & Wedel SVPCA 2019 Slideshow
A PDF rendering of the PowerPoint slideshow that accompanied the talk.