Ornithopod Craniodental Remains from the Griman Creek Formation (Cenomanian), New South Wales, Australia

Abstract

<p>Ornithopods are a clade of dinosaurs generally accepted to include non-iguanodontian ornithopods, non-hadrosaurid iguanodontians, and hadrosaurids. While acknowledging the phylogenetic placement of traditional non-iguanodontian ornithopods, or ‘basal ornithopods’, within Ornithopoda lacks consensus, this thesis will continue to use the traditional hypothesis and refer to these taxa as ornithopods.</p> <p>In Australia, ornithopod remains are known almost exclusively from the Cretaceous Period (~145–66 million years ago [Ma]), with isolated jaws amongst the best-represented ornithopod fossils. Although incomplete craniodental remains are not as ideal as more complete skeletons for phylogenetic study, they are taxonomically informative and can give important insights into the palaeoecology and evolution of the clade. Furthermore, the use of sophisticated scanning technology, such as synchrotron radiated and neutron scattering scanning employed in this study, enables highly detailed comparisons that could not be otherwise performed. One historical view of Australian ornithopod palaeobiogeography is that the high-latitude environment in southern Australia during the upper-Barremian to lower Albian of the Early Cretaceous (~127–110 Ma) was dominated by small-bodied non-iguanodontian ornithopods, whereas large-bodied ornithopods, represented by the iconic Australian taxon <i>Muttaburrasaurus</i>, was a dominant ornithopod form in more northern latitudes of the Australian mid-Cretaceous (~102–100 Ma). However, an emerging picture is that small-bodied noniguanodontian ornithopods may have been equally well represented across eastern Australia during at least the mid-Cretaceous and that large-bodied iguanodontians were excluded from the high-latitudes palaeopolar region in present-day southern Victoria.</p> <p>The recovery of new ornithopod material is therefore essential to further our understanding of Australian ornithopod diversity, disparity, phylogenetic relationships, and biogeography, which form the aims of this thesis. These aims are addressed in the following three chapters.</p> <p><b>Chapter 1:</b> The anatomy, evolution, and palaeobiogeography of Australian non-hadrosaurid ornithopods with a review of non-hadrosaurid ornithopod palaeoneurology.</p> <p>This chapter is a literature review on our current understanding of Australian nonhadrosaurid ornithopod diversity. A summary of the anatomy, evolution, and palaeobiogeography for each of the named Australian ornithopods is provided. A section on ornithopod palaeoneurology is additionally provided and its importance to ornithopod palaeobiogeographic understanding is discussed. </p> <p><b>Chapter 2:</b> Description of three small-bodied ornithopod dentaries from the Griman Creek Formation.</p> <p>In this chapter, the systematic descriptions of three non-iguanodontian ornithopod toothbearing dentaries from the Griman Creek Formation in New South Wales, Australia, is provided. Two of these jaws were included in a previous study; however, this study utilizes neutron scanning to provide a more detailed analysis than possible in the previous work. The third dentary is a new specimen not previously studied. A phylogenetic analysis is conducted to provide hypotheses of Australian ornithopod phylogenetic relationships. </p> <p><b>Chapter 3:</b> Palaeoneurology of the non-hadrosaurid iguanodontian <i>Fostoria dhimbangunmal<i> from the Griman Creek Formation in New South Wales, Australia.</p> <p>This chapter includes the first complete endocast description of any Australian ornithopod. Using computed tomography scans of the braincase of <i>Fostoria dhimbangunmal</i>, this paper provides insights into the ecology of <i>Fostoria<i> and brain evolution within Ornithopoda as a whole.</p>