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489 27 Australia’s Polar Early Cretaceous Dinosaurs Thomas H. Rich* and Patricia Vickers-Rich Although meager in terms of the number and completeness of the specimens known of it, the Early Cretaceous dinosaurs of southeastern Australia are notable for being a significant part of a polar tetrapod assemblage that during the Aptian occupied the coldest terrestrial region known on earth for the entire Mesozoic Era. As such, it provides a unique perspective regarding the physiology of dinosaurs. Facing the Southern Ocean in the southeastern corner of Australia are coastal exposures locally termed shore platforms. Fossiliferous Early Cretaceous fluviatile deposits extending for just under 150 km form a significant part of these shore platforms (Fig. 27.1). Because the typical width of these shore platforms is about 20 m, there are roughly 3 km2 of outcrop that has yielded a variety of polar Cretaceous fossil vertebrates. Although the same rock units occur inland, they are typically vegetated, and where they do occasionally crop out, they are deeply weathered, unlike the fresh coastal outcrops, which are typically unweathered and well exposed as a result of active erosion by the ocean waves pounding against them (Figs. 27.2, 27.3). Institutional abbreviation. NMV P, Paleontology Collection of the Museum Victoria, Melbourne, Australia. There are two main areas of continental dinosaur-bearing Cretaceous rocks in southeastern Australia. They flank the city of Melbourne, with one to the east and a more extensive one to the west (Fig. 27.1). Those yielding fossil vertebrates to the east make up the Wonthaggi Formation of the Strzelecki Group (Fig. 27.4). Where fossil tetrapods occur in this unit, palynomorphs date it as Early Aptian (Rich et al., 1999). More extensive in extent than the coastal outcrops of the Wonthaggi Formation are those of the Eumerella Formation, Otway Group, to the west of Melbourne (Fig. 27.5). Where fossil tetrapods occur in that unit, palynomorphs date it as Early Albian (Wagstaff and McEwen-Mason, 1989). Although fossil tetrapods have been recovered from a number of sites on these coastal outcrops, the bulk of specimens have come from two localities , Dinosaur Cove in the Eumerella Formation of the Otway Group (Figs. 27.6–27.7) and Flat Rocks in the Wonthaggi Formation of the Strzelecki Group (Figs. 27.8–27.9). Except for 1988, the former was worked annually from 1984 to 1994. The latter has been worked annually from 1994 to the present. Background Geology and Biota Rich and Vickers-Rich 490 The Cretaceous rocks of Victoria have yielded bones and teeth of fossil tetrapods in four different facies. Fossil feathers have been found in a fifth one. The general setting of these fossil sites was a floodplain that formed the floor of the rift valley between Australian and Antarctica as those two landmasses were in the initial stage of separation from one another during the Late Mesozoic Era. Across this floodplain flowed broad rivers in a generally westward direction , much like the modern Lena River of northern Siberia. The sea lay about 2,000 km to the west of the fossil sites during the Aptian but had encroached eastward by the Albian to only a few hundred kilometers west of them (Fig. 27.10). The physical evidence for this environmental interpretation was described by Bryan et al. (1997, 91) as a “series of multi-storied sheet flood to braided-river-like channel complexes, up to 200 m thick, separated by overbank sequences ranging between 5 and 100 m in thickness . Internally, the channel complexes are characterized by thick packages of planar cross-stratified, massive, and low-angle cross-stratified sandstone. The range of lithofacies coupled with the remarkable uniformity in sand grain size suggests the sediments were deposited by a fluvial system subject to high energy discharge events.” Isolated fossil tetrapod bones have been found in the sheet flood to braided river–like channel facies, but only rarely. The bulk of the fossil tetrapod bones and teeth found in Victoria have been recovered from lag concentrations in the overbank deposits mentioned by Bryan et al. (1997). These lag deposits are thought to have formed as the result of evulsion events occurring when levees of large rivers were Taphonomy 27.2. Unweathered outcrop of the Eumerella Formation of the Otway Group in Dinosaur Cove. The device pictured is the basket of a flying fox, 305 m long, utilized to lower equipment 90 m vertically into Dinosaur Cove and raise those same items as well as the excavated...

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