Ornithopod jaws from the Lower Cretaceous Eumeralla Formation, Victoria, Australia, and their implications for polar neornithischian dinosaur diversity

ABSTRACT

Ornithopod dinosaurs are relatively common in the Cretaceous of Australia, particularly in the state of Victoria, which has yielded five taxa to date: two from the upper Strzelecki Group (upper Barremian–lower Aptian), and three from the Eumeralla Formation (upper Aptian–upper Albian). Whereas four of these are based solely on cranial material, Diluvicursor pickeringi is represented by a partial postcranium and is the only ornithopod specimen heretofore reported from the Eric the Red West (ETRW) site. Herein, we describe nine ornithopod dentulous elements from the Eumeralla Formation: seven from ETRW, and two from nearby sites. The four ETRW maxillae are divided into three morphotypes that are morphologically compatible with Leaellynasaura amicagraphica, Atlascopcosaurus loadsi, and cf. Galleonosaurus dorisae, respectively. Although this implies that Diluvicursor might not represent a distinct taxon, this is circumstantial. The new Leaellynasaura maxillae are evidently adult exemplars, contrasting with the juvenile holotype, whereas the sole Atlascopcosaurus maxilla is more complete than all previously referred specimens; consequently, revised diagnoses of both taxa are presented. Finally, the presence in the Eumeralla Formation of cf. Galleonosaurus—otherwise known only from the upper Strzelecki Group—implies that this taxon persisted from the Barremian to the Albian, and potentially indicates remarkable environmental stability in southeast Australia during the late Early Cretaceous.

ACKNOWLEDGMENTS

The authors would like to thank: all Dinosaur Dreaming Crew who have been part of the excavations at ETRW, particularly those whose discoveries and collections have been used in this report (G. Caspar, M. Cleeland, M. Walters); D. Bellingham for providing images of the ventral surface of NMV P253862; L. Kool and the late D. Pickering for preparing the specimens; T. Ziegler (Museums Victoria) for discussions and facilitating access to the collection and various other resources including the archive of 3D data used in this study; Parks Victoria for provision of permits to work on their lands (especially E. Dalgleish-Wright and rangers B. Martin and G. Summers); the Department of Environment, Land, Water & Planning (especially S. Hadden and M. Kelly); Monash University for the access to Micro-CT scanner and data used in this report; Swinburne University of Technology where this research was undertaken as part of R.J.D’s Honours project in 2019; J. Bevitt and the Australian Synchrotron for Leaellynasaura (NMV P185991) synchrotron data; B. Freshwater (St. Vincent’s Hospital, Melbourne) for CT scanning NMV P186352 and NMV P221082; and C. Paragnani for discussions and assistance with specimen photography. R.J.D. would like to thank A. Dean, T. Hatfield, S. Hooley and A. Wall for assistance reviewing various drafts of this report and A. Hooley for 3D printing models of key specimens for study. S.F.P. would like to thank: the Winston Churchill Memorial Trust for a Churchill Fellowship (awarded in 2017), which enabled firsthand observation of several Argentinian ornithopod specimens in October–December 2018; M. Ezcurra (Museo Argentino de Ciencias Naturales ‘Bernardino Rivadavia’) for facilitating access to Loncosaurus and Morrosaurus; M. Reguero and J. Desojo (Museo de La Plata) for facilitating access to Trinisaura; R. Coria and L. Coria (Museo Municipal Carmen Funes) for facilitating access to Anabisetia; J. Calvo and J. Mansilla (Museo de Geología y Paleontología de la Universidad Nacional del Comahue) for facilitating access to Gasparinisaura and Macrogryphosaurus; I. Cerda and G. Riccono (Museo Regional de Cinco Saltos) for facilitating access to Gasparinisaura; R. Martínez and M. Luna (Universidad Nacional de la Patagonia San Juan Bosco) for facilitating access to Notohypsilophodon and Sektensaurus; and C. Aguilar, P. Campan, Y. Güemes and T. Bellini (Museo Regional Provincial Padre Manuel Jesús Molina) for facilitating access to Talenkauen. P.V.R wishes to thank the National Geographic Society whose grants over the years have led to the discovery of many of these specimens; D. Turnbull and the Bunurong People, R. Collopy of the Eastern Maar; Murrundindi of the Wurundjeri People for welcoming us onto their Lands, and for their ongoing interest and assistance in our work; the Evans and Denny families; the Otway Lighthouse; Bimbi Park, and the many locals along the Bass and Otway coasts for their help in so many ways. Finally, the authors wish to thank P. Bell, an anonymous reviewer, and editor A. Balanoff whose feedback greatly improved the quality of this manuscript.