A large-clawed theropod (Dinosauria: Tetanurae) from the Lower Cretaceous of Australia and the Gondwanan origin of megaraptorid theropods |
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| Institution: | 1. School of Environmental and Rural Science, University of New England, Armidale, NSW 2351, Australia;2. Museo Geologico Giovanni Capellini, Università di Bologna, via Zamboni 63, 40126 Bologna, Italy;3. Dipartimento di Scienze Biologiche, Geologiche e Ambientali, Alma Mater Studiorum, Università di Bologna, Via Zamboni 67, 40126 Bologna, Italy;4. Australian Opal Centre, P.O. Box 229, Lightning Ridge, NSW 2834, Australia;1. School of Environmental and Rural Science, University of New England, Armidale, NSW 2351, Australia;2. Museo Geologico Giovanni Capellini, Università di Bologna, via Zamboni 63, 40126 Bologna, Italy;3. Dipartimento di Scienze Biologiche, Geologiche e Ambientali, Alma Mater Studiorum, Università di Bologna, Via Zamboni 67, 40126 Bologna, Italy;4. Australian Opal Centre, P.O. Box 229, Lightning Ridge, NSW 2834, Australia;1. Department of Earth Sciences, Uppsala University, Uppsala, Sweden;2. Australian Age of Dinosaurs Museum of Natural History, The Jump-Up, Winton, Queensland, Australia;3. Department of Earth Sciences, University College London, Gower Street, London WC1E 6BT, United Kingdom;4. Department of Earth Science and Engineering, Imperial College London, South Kensington Campus, London SW7 2AZ, United Kingdom;5. Geosciences, Queensland Museum, Hendra, Queensland, Australia |
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| Abstract: | Megaraptoridae comprises a clade of enigmatic Gondwanan theropods with characteristic hypertrophied claws on the first and second manual digits. The majority of megaraptorids are known from South America, although a single genus (Australovenator) plus additional indeterminate material is also known from Australia. This clade has a controversial placement among theropods, and recently has been interpreted alternatively as a carcharodontosaurian or a tyrannosauroid lineage. We describe new fragmentary but associated postcranial remains from the opal fields of Lightning Ridge (middle-Albian, Griman Creek Formation) in north-central New South Wales. The new unnamed taxon exhibits a number of unusual features that suggest the presence of a hitherto unrecognised Australian megaraptorid. From an Australian perspective, the Lightning Ridge taxon predates Australovenator by ca. 10 Ma and is minimally coeval with megaraptoran material reported from the Eumeralla Formation of Victoria (but potentially 6.1–9.5 Ma younger). It is also notable as the largest predatory dinosaur yet identified from Australia and is only the second theropod known from more than a single element. A Bayesian phylogenetic approach integrating morphological, stratigraphic and palaeogeographic information tested both the carcharodontosaurian and tyrannosauroid placements for Megaraptora. Regardless of the preferred placement among Tetanurae, rigorous palaeobiogeographic analyses support an Asian origin of Megaraptora in the latest Jurassic (about 150–135 Ma), an Early Cretaceous (about 130–121 Ma) divergence of the Gondwanan lineage leading to Megaraptoridae, and an Australian root for megaraptorid radiation. These results indicate that Australia's Cretaceous dinosaur fauna did not comprise simply of immigrant taxa but was a source for complex two-way interchange between Australia–Antarctica–South America leading to the evolution of at least one group of apex predatory dinosaurs in Gondwana. |
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