Bernissart Dinosaurs and Early Cretaceous Terrestrial Ecosystems

28. Assessment of the Potential for a Jehol Biota–like Cretaceous Polar Fossil Assemblage in Victoria, Australia

505 28 Assessment of the Potential for a Jehol Biota–like Cretaceous Polar Fossil Assemblage in Victoria, Australia Thomas H. Rich*, Li Xiao-Bo, and Patricia Vickers-Rich An abundance of exquisitely preserved birds, mammals, and feathered dinosaurs , among other fossils, has been recovered from the Early Cretaceous Jehol Biota of northeastern China. The similarities, both in the nature of those deposits and the plant, arthropod, and fish fossils they contain, to those from the lacustrine facies of the Strzelecki Group of southwestern Gippsland, Victoria, Australia, suggest that a prolonged, systematic search of the latter could yield tetrapods of similar quality. Although fossil remains of Early Cretaceous fish, arthropods, and plants have been known from the Jehol fossil province of northeastern China for more than a century, it has only been in the past two decades that the presence in those deposits of exquisitely preserved tetrapods have been recognized (Chang, 2003). A visit in June 2009 by one of us (T.R.) to one site in particular where the Jehol Biota occurs—the visitor facility of the Sihetun Landscape Fossil Bird National Geopark of Chaoyang City—demonstrated that a striking similarity exists between it and the Aptian (Early Cretaceous) Koonwarra site in southwestern Gippsland, Victoria, Australia (Rich et al., 2009; Fig. 28.9, Fig. 27.1). In both are seen a suite of similar fossil arthropods, small fish, and plant matter (Fig. 28.1). The Koonwarra fossils have been described by Waldman (1971), Drinnan and Chambers (1986), and Jell and Duncan (1986), and the age determination was made by Dettmann (1986). The fossils at the Sihetun Visitor Facility for the most part occur in fine-grained lacustrine deposits laid down in a quiet, anoxic environment with little or no sign of bioturbation. Specifically, the fossiliferous units are alternating dark and light layers of fine-grained shales, each individual layer between 0.1 and 1 mm thick. The laminar nature of the fossiliferous rock suggests that there was little or no bioturbation, and presumably the water column was stratified for at least part of the year, rather than mixed, and the bottom water was anoxic (Liu et al., 2002; Fürsich et al., 2007). The lithology of the Koonwarra site is much the same with finely laminated shales indicative of a lacustrine environment, which likewise suggests an anoxic environment with little or no sign of bioturbation (Waldman 1971). Half a dozen feathers from the Koonwarra site are the only evidence thus far for the presence of tetrapods. However, although the feathers are few in number, they are significant for demonstrating not only that Background Rich et al. 506 tetrapods were present in the area, but also that the preservation of such fossils did occur in the depositional environment at Koonwarra, just as it often did where the Jehol Biota is preserved. The similarities between the Jehol and Koonwarra sediments, together with the nature of the fossils that occur at both, suggest that tetrapod skeletons might be found at Koonwarra or elsewhere in the lacustrine facies of the Strzelecki Group if a concerted effort is made to do so. At the visitor’s center of the Sihetun Landscape Fossil Bird National Geopark of Chaoyang City, under cover in a quite substantial building, are exposed 31 fossil vertebrates found over an area of approximately 400 m2 (Fig. 27.2). The fossils were seemingly distributed at random (Fig. 27.3). There were 26 plastic boxes enclosing the fossil tetrapods and one large fish (Figs. 27.4, 27.5). Most often there was one fossil vertebrate in each box, but three of these boxes each had two specimens, and there was another box containing three specimens. Because the purpose of this exhibit was to show the most prominent fossil vertebrates in place, none had been removed, and thus the distribution of the fossils and their abundance is accurately known. Investigation of the Jehol Biota 28.2. Visitor facility of the Sihetun Landscape Fossil Bird National Geopark of Chaoyang City, Liaoning province, People’s Republic of China. The area of approximately 400 m2 , where the 31 fossil vertebrates are exposed, is under the part of the building with the arched roof to the left of the main entrance. The area to the right has two floors of exhibits. Jehol Biota–like Cretaceous Polar Fossil Assemblage in Australia 507 28.3. Map of the Sihetun fossil site. East is at the top, south is to...