Refined age and geological context of two of Australia’s most important Jurassic vertebrate taxa (Rhoetosaurus brownei and Siderops kehli), Queensland

• Published in: Gondwana research Vol. 76; pp. 19 - 25
• Main Authors: Todd, Christopher N., Roberts, Eric M., Knutsen, Espen M., Rozefelds, Andrew C., Huang, Hui-Qing, Spandler, Carl
• Format: Journal Article
• Language: English
• Published: Elsevier B.V 01.12.2019
• Subjects: Evergreen Formation; Jurassic; Rhoetosaurus brownei; Siderops kehli; Walloon Coal Measures; Evergreen Formation; Rhoetosaurus brownei; Jurassic; Siderops kehli; Walloon Coal Measures
• ISSN: 1342-937X; 1878-0571
• DOI: 10.1016/j.gr.2019.05.008

Australia’s Jurassic vertebrate fossil record remains extremely sparse with only two dinosaur taxa and two temnospondyl amphibians identified to date. Of these, the spectacular and extremely well-preserved giant amphibian, Siderops kehli, and the only known pre-Cretaceous sauropod in Australia, Rhoetosaurus brownei, are perhaps the most important. The age of both specimens, and the stratigraphic context of Rhoetosaurus brownei, are weakly constrained and imprecisely defined, limiting our understanding of their evolutionary relationships within a broader Gondwanan context. To clarify and contextualise the evolutionary relationships and ages of these two iconic Jurassic taxa, we used UPb detrital zircon geochronology to date the sandstone matrix from around the bones of the historic museum specimens. The robust maximum depositional age for Siderops was calculated at 176.6 Ma ± 2 Ma, indicating that it is no older than late Toarcian, which refines existing biostratigraphic estimates. The Rhoetosaurus maximum depositional age was determined to be 162.6 ± 1.1 Ma, no older than early Oxfordian, demonstrating that the fossils are younger than expected, and definitely recovered from the Walloon Coal Measures. [Display omitted] •Maximum depositional age of Rhoetosaurus brownei is constrained to 162.6 ± 1.1 Ma.•Maximum depositional age of Siderops kehli is constrained to 176.6 ± 2.0 Ma.•Detrital zircons are useful for refining the age of fossils in museum collections.