Early Cretaceous polar biotas of Victoria, southeastern Australia—an overview of research to date

Although Cretaceous fossils (coal excluded) from Victoria, Australia, were first reported in the 1850s, it was not until the 1950s that detailed studies of these fossils were undertaken. Numerous fossil localities have been identified in Victoria since the 1960s, including the Koonwarra Fossil Bed (Strzelecki Group) near Leongatha, the Dinosaur Cove and Eric the Red West sites (Otway Group) at Cape Otway, and the Flat Rocks site (Strzelecki Group) near Cape Paterson. Systematic exploration over the past five decades has resulted in the collection of thousands of fossils representing various plants, invertebrates and vertebrates. Some of the best-preserved and most diverse Hauterivian–Barremian floral assemblages in Australia derive from outcrops of the lower Strzelecki Group in the Gippsland Basin. The slightly younger Koonwarra Fossil Bed (Aptian) is a Konservat-Lagerstätte that also preserves abundant plants, including one of the oldest known flowers. In addition, insects, crustaceans (including the only syncaridans known from Australia between the Triassic and the present), arachnids (including Australia’s only known opilione), the stratigraphically youngest xiphosurans from Australia, bryozoans, unionoid molluscs and a rich assemblage of actinopterygian fish are known from the Koonwarra Fossil Bed. The oldest known—and only Mesozoic—fossil feathers from the Australian continent constitute the only evidence for tetrapods at Koonwarra. By contrast, the Barremian–Aptian-aged deposits at the Flat Rocks site, and the Aptian–Albian-aged strata at the Dinosaur Cove and Eric the Red West sites, are all dominated by tetrapod fossils, with actinopterygians and dipnoans relatively rare. Small ornithopod (=basal neornithischian) dinosaurs are numerically common, known from four partial skeletons and a multitude of isolated bones. Aquatic meiolaniform turtles constitute another prominent faunal element, represented by numerous isolated bones and articulated carapaces and plastrons. More than 50 specimens—mostly lower jaws—evince a high diversity of mammals, including monotremes, a multituberculate and several enigmatic ausktribosphenids. Relatively minor components of these fossil assemblages are diverse theropods (including birds), rare ankylosaurs and ceratopsians, pterosaurs, non-marine plesiosaurs and a lepidosaur. In the older strata of the upper Strzelecki Group, temnospondyl amphibians—the youngest known worldwide—are a conspicuous component of the fauna, whereas crocodylomorphs appear to be present only in up-sequence deposits of the Otway Group. Invertebrates are uncommon, although decapod crustaceans and unionoid bivalves have been described. Collectively, the Early Cretaceous biota of Victoria provides insights into a unique Mesozoic high-latitude palaeoenvironment and elucidates both palaeoclimatic and palaeobiogeographic changes throughout more than 25 million years of geological time.