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in Kotevski, Duncan, Pentland, Rule, Vickers-Rich, ... et Poropat, 2023. |
Highlights:
• First non-mandibular skull element reported for an Australian non-avian theropod.
• Geologically oldest megaraptorid frontal element worldwide.
• Megaraptorid and non-megaraptorid megaraptorans present in upper Strzelecki Group.
Abstract
Cretaceous (non-avian) theropod dinosaurs from Australia are poorly understood, primarily because almost all specimens described thus far comprise isolated postcranial elements. In Australia, only three non-dental cranial elements pertaining to Theropoda have been reported: the left and right dentaries of Australovenator wintonensis from the Winton Formation (Cenomanian–lowermost Turonian) of Queensland, and an isolated surangular from the Eumeralla Formation (lower Albian) of Victoria. Herein, we report the first evidence of non-mandibular cranial material of a non-avian theropod from Australia: a left frontal and fused parietal fragment from the Lower Cretaceous (lower Aptian) upper Strzelecki Group of Victoria. The specimen shares several synapomorphies with the frontals assigned to Megaraptoridae, including an anteroposteriorly elongate postorbital articulation and a truncated nasal articular surface. Accordingly, we regard this frontal as Megaraptoridae gen. et sp. indet. We performed both parsimony-based and Bayesian-based phylogenetic analyses to support our assignment, and both analyses support a placement within Megaraptoridae. However, this specimen appears to possess plesiomorphic characters relative to other megaraptorid frontals, lacking dorsoventrally high walls of bone that emarginate the nasal and prefrontal articular surfaces. The plesiomorphies of this specimen have implications for the evolution of the megaraptoran skull roof, suggesting the acquisition of specialised adaptations for longirostry over time. This specimen improves the limited record of Cretaceous Australian theropod cranial remains, and provides limited support for the hypothesis that Megaraptoridae might have originated in Australia.
Keywords: Gondwana, Australia, Dinosauria, Theropoda, Cretaceous, Megaraptoridae
THEROPODA Marsh, 1881.
TETANURAE Gauthier, 1986.
COELUROSAURIA von Huene, 1914.
MEGARAPTORA Benson et al. 2010.
MEGARAPTORIDAE Novas et al. 2013.
Megaraptoridae gen. et sp. indet.
Referred material: NMV P229038: An isolated, almost complete left frontal, fused to a fragment of the left parietal (Fig. 3).
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| Graphical abstract depicting major research findings of this report. Clockwise from top: Geological scale indicating ages of known megaraptoran frontals; Locality map of the upper Strzelecki Group portraying localities yielding Megaraptora and Megaraptoridae fossils (map data cited in Fig. 1); Life reconstruction of Victorian megaraptorid with approximate life position of NMV P229038 shown in silhouette and in dorsal view (illustration by Ruairidh J. Duncan); Map of southern hemisphere with modern geographic borders showing approximate location of constituent Gondwanan continents and fossil locality at ∼110Ma. Southern hemisphere map derived and adapted from Rich et al. (2002). Chronostratigraphic data derived from Cohen et al. (2013; updated). |
Jake Kotevski, Ruairidh J. Duncan, Adele H. Pentland, James P. Rule, Patricia Vickers-Rich, Thomas H. Rich, Erich M.G. Fitzgerald, Alistair R. Evans and Stephen F. Poropat. 2023. A megaraptorid (Dinosauria: Theropoda) Frontal from the upper Strzelecki Group (Lower Cretaceous) of Victoria, Australia. Cretaceous Research. In Press, 105769. DOI: 10.1016/j.cretres.2023.105769
