The integration of phylogenetics, phylogeography and palaeoenvironmental studies is providing major insights into the historical forces that have shaped the Earth's biomes. Yet our present view is biased towards arctic and temperate/tropical forest regions, with very little focus on the extensive arid regions of the planet. The Australian arid zone is one of the largest desert landform systems in the world, with a unique, diverse and relatively well-studied biota. With foci on palaeoenvironmental and molecular data, we here review what is known about the assembly and maintenance of this biome in the context of its physical history, and in comparison with other mesic biomes. Aridification of Australia began in the Mid-Miocene, around 15 million years, but fully arid landforms in central Australia appeared much later, around 1-4 million years. Dated molecular phylogenies of diverse taxa show the deepest divergences of arid-adapted taxa from the Mid-Miocene, consistent with the onset of desiccation. There is evidence of arid-adapted taxa evolving from mesicadapted ancestors, and also of speciation within the arid zone. There is no evidence for an increase in speciation rate during the Pleistocene, and most arid-zone species lineages date to the Pliocene or earlier. The last 0.8 million years have seen major fluctuations of the arid zone, with large areas covered by mobile sand dunes during glacial maxima. Some large, vagile taxa show patterns of recent expansion and migration throughout the arid zone, in parallel with the ice sheet-imposed range shifts in Northern Hemisphere taxa. Yet other taxa show high lineage diversity and strong phylogeographical structure, indicating persistence in multiple localised refugia over several glacial maxima. Similar to the Northern Hemisphere, Pleistocene range shifts have produced suture zones, creating the opportunity for diversification and speciation through hybridisation, polyploidy and parthenogenesis. This review highlights the opportunities that development of arid conditions provides for rapid and diverse evolutionary radiations, and re-enforces the emerging view that Pleistocene environmental change can have diverse impacts on genetic structure and diversity in different biomes. There is a clear need for more detailed and targeted phylogeographical studies of Australia's arid biota and we suggest a framework and a set of a priori hypotheses by which to proceed.

Australia's oldest human remains, found at Lake Mungo, include the world's oldest ritual ochre burial (Mungo III) and the first recorded cremation (Mungo I). Until now, the importance of these finds has been constrained by limited chronologies and palaeoenvironmental information. Mungo III, the source of the world's oldest human mitochondrial DNA, has been variously estimated at 30 thousand years (kyr) old, 42-45 kyr old and 62 +/- 6 kyr old, while radiocarbon estimates placed the Mungo I cremation near 20-26 kyr ago. Here we report a new series of 25 optical ages showing that both burials occurred at 40 +/- 2 kyr ago and that humans were present at Lake Mungo by 50-46 kyr ago, synchronously with, or soon after, initial occupation of northern and western Australia. Stratigraphic evidence indicates fluctuations between lake-full and drier conditions from 50 to 40 kyr ago, simultaneously with increased dust deposition, human arrival and continent-wide extinction of the megafauna. This was followed by sustained aridity between 40 and 30 kyr ago. This new chronology corrects previous estimates for human burials at this important site and provides a new picture of Homo sapiens adapting to deteriorating climate in the world's driest inhabited continent.

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The story of the Willandra Lakes is also the story of those ancient people who lived there. The landforms, sediments and soils provide the environmental framework within which the patterns of human occupation must be interpreted. The original stratigraphic system involved just two units, the Mungo and Zanci. Two additional units are now defined; one incorporating complexities between Mungo and Zanci, the Arumpo Unit, and a second to acknowledge the reality of a lake full phase near l8ka cal., postdating Zanci aridity of the last glacial maximum. This new unit is defined from Lake Mulurulu as the Mulurulu Unit.Improved facies analysis from data involving lake sediments, freshwater quartz beach sands (QBSs) and lake-dry pelletal clay dunes (PCDs) helps refine the sequence of environmental changes. Revision of radiocarbon chronologies with conversion to calendar years, and additional dates (radiocarbon, luminescence, amino acid racemisation) permit new age definitions of major environmental changes and human-land interactions.Following a lake-full phase (Lower Mungo time) from before about 55ka cal., a phase of PCD accumulation is dated to near 40ka cal. defining an early stage of hydrologic stress. Progressive water level oscillations continued (Arumpo time) culminating in major drying with deflation and extension of regional dune building over large areas of the Murray Basin near 20ka cal. (Zanci time). Freshwater returned temporarily to the Willandra lakes about l8-l9ka cal.Throughout the period 25-l9ka cal. spanning the glacial maximum, the apparent absence of fish and unionid mussels may reflect major temperature depression corresponding also to the period of maximum aridity. The ecological stress experienced at this time had an immense impact on the landscape, plants and especially larger animals, requiring new adaptive responses from human occupants. Early grinding techniques, pre-dating evidence of seed grinding, are suggested.Reconstruction of the sedimentary sequence at the main archaeological site at Joulni reveals a pre-Mungo unit deep in the sequence of a system developed by barrier construction isolating the Joulni Plain from the main lake. Analogous conditions at Lake Victoria today mirror development of the Joulni archaeological site. Oldest artefacts occurring within this un-named unit are dated beyond 45ka cal.Human occupation on the lakeshore barrier system at Lake Mungo involved aquatic harvesting (fish and shellfish) associated with human burials before the onset of PCD deposition, pre-40kaSchool of Earth Sciences, University of Melbourne, Parkville 3052. bowler@earthsci.unimelb.edu.au 120 cal. The association here of the complex burial ritual (Mungo III) involving anointing with ochre at this time presents one of the dramatic mysteries of ancient human cultural development. In death, the story of that person illuminates our understanding of those ancient occupants and the Ice Age environments that supported them.