The past, present and future of Jensen’s Big Three sauropods

13th August 2019


1 - Western University of Health Sciences [sic]
2 - University of Bristol, Earth Sciences [sic]

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.

[Slides PPT] [Slides PDF] [Abstracts volume].

Feedback to <> is welcome!