Over 2000 kilometres separate the two sites which form the World Heritage property. Riversleigh (10 000 hectares), located in north western Queensland, is confined to the watershed of the Gregory River. The site at Naracoorte, South Australia, covers 300 hectares and is located in flat country, punctuated by a series of stranded coastal dune ridges that run parallel to the present coastline.
Riversleigh is one of the world's richest Oligo-Miocene mammal records, linking that period (15-25 million years ago) to the predominantly modern assemblages of the Pliocene and Pleistocene epochs. The site provides exceptional examples of middle to late Tertiary mammal assemblages, in a continent whose mammalian evolutionary history has been the most isolated and most distinctive in the world.
The extensive fossil deposits at Riversleigh are encased in hard, rough limestone, which was formed in lime-rich freshwater pools. They span a record of mammal evolution of at least 20 million years in length, providing the first records for many distinctive groups of living mammals, such as marsupial moles and feather-tailed possums, as well as many other unique and now extinct Australian mammals such as 'marsupial lions'.
The variety of deposits at Riversleigh has led to an understanding of how the environment has changed over time from a rich rainforest community to semi-arid grassland, and how the animals that lived in it have changed too.
The discovery of the fossils at Riversleigh has profoundly altered the understanding of Australia's mid-Cainozoic vertebrate diversity. The remains of a 15 million-year-old monotreme has provided new information about this highly distinctive group of mammals, and several Tertiary thylacines have been identified. Placental mammals are represented by more than 35 bat species and the Riversleigh fossil bat record is the richest in the world.
In stark contrast to the semi-arid conditions at Riversleigh stand the cool caves at Naracoorte. Here are fossils that document a distinctive fauna, with the ancestors of modern species alongside the doomed giants of a world that was about to be devastated by climatic changes.
The fossils in the Naracoorte Caves illustrate faunal change spanning several ice ages, highlighting the impacts of both climatic change and humankind on Australia's mammals from at least 350 000 years before the present.
Further research at the Naracoorte Caves sites is expected to document a series of snapshots of Pleistocene life in south east Australia, including details of climate and vegetation associated with the fauna. Recent geological research suggests that deposits of Pliocene and even Miocene age could be found at the site, thus providing closer links with the site at Riversleigh.
Specimens representing 99 vertebrate species have been discovered, ranging in size from very small frogs to buffalo-sized marsupials. These include exceptionally preserved examples of the Australian Ice Age megafauna, as well as a host of modern species such as the Tasmanian devil, thylacine and others. The Naracoorte fossils span the probable time of the arrival of humans in Australia, and this is valuable in analysing the complex relationships between humans and their environment.
Both sites provide evidence separately of key stages in the evolution of the fauna of the world's most isolated continent. The history of mammal lineages in modern Australia can be traced through these fossil deposits and, as a consequence, there is a better understanding of the conservation status of living mammals and their communities.
The sites, each highly significant in its own right, are presented as a serial World Heritage nomination. Together they represent the key stages in the development of Australia's mammal fauna. While there are other important Australian fossil mammal sites, Riversleigh and Naracoorte are outstanding for the extreme diversity and the quality of preservation of their fossils. They also provide links through time that unify the biotas of the past with those of today in the Wet Tropics of Queensland, the Central Eastern Rainforest Reserves (Australia) and Kakadu National Park World Heritage properties. |
