Fossils in Riversleigh, QLD
Fossil fauna from the Riversleigh site have altered our understanding about Australia's mid-Cainozoic vertebrate diversity.
Where is Riversleigh?
Riversleigh (10,000ha) comprises the southern section of Lawn Hill National Park in north-west Queensland (18°59'-19°08'S, 138°34'-138°43'E). Riversleigh was gazetted as part of the Lawn Hill National Park under the Queensland National Park and Wildlife Act 1975 in 1984. Additionally, because of its unrivalled richness, the expanse of time covered by its record, and the quality of the fossils it yields, Riversleigh was declared a World Heritage site in 1994.
Why is Riversleigh important?
Fossil fauna from the Riversleigh site have altered our understanding about Australia's mid-Cainozoic vertebrate diversity. A 15 million-year-old complete skull and nearly complete dentition of the monotreme Obdurodon dicksoni (Archer et al. 1992, 1993) has provided new information about this highly distinctive group of mammals.
The recently extinct marsupial Thylacine, Thylacinus cynocephalus, also known as the Tasmanian Tiger, was the largest living mammalian carnivore in Australia. Before Riversleigh's fossil record began to unfold, there was only one Tertiary thylacine species known, but now different thylacines have been identified from Riversleigh's Oligo-Miocene faunas (Muirhead & Archer 1990; Muirhead 1993). This record has been used (Archer l991a, Archer et al., 1992) to demonstrate the potential conservation value of understanding the prehistory of a group. Although, in this case, understanding was too late to prevent the extinction of the Thylacine in the 1930s. Other ancestral marsupial forms found at Riversleigh include moles, bandicoot, marsupial 'lions', koala, wombat, kangaroo and possums. Placental mammals are represented by more than 35 bat species, and the Riversleigh fossil bat record is considered one of the richest in the world.
There are large number of visible archaeological traces of Aboriginal occupation and sites of cultural significance at Riversleigh, particularly near the rivers. The site at Riversleigh lies on the south-western boundary of the Waanyi Aboriginal clan territory (Oates and Oates 1970, Oates 1975, Tindale 1974). No Aboriginal people currently live in the site, although appropriate involvement is sought in the management of identified cultural sites.
Fossil time period: Riversleigh
The last remnant of the supercontinent Gondwana finally separated into Australia and Antarctica between 30 and 40 million years ago. Isolated on an enormous northward-drifting raft the inhabitants of the Australian continent evolved and diversified over millions of years as the climate cycled through periods of warm and cool, wet and dry.
From more than 250 fossil-rich sites at Riversleigh hundreds of new species have been described from thousands of well-preserved specimens. There are many yet to be described and many more fossil sites waiting to be discovered. Nowhere else in the world is there such a rich, detailed and continuous fossil record of the changes in fauna, habitat and climate at a single locality.
Our understanding of the origins, evolution and history of many of Australia's vertebrate groups has been greatly enhanced by the fossil record of Riversleigh's rich Oligo-Miocene habitats. These Tertiary faunas include ancestors and representatives of the kangaroos, rat-kangaroos, bandicoots, wombats, marsupial moles, thylacines, dasyurids, koalas, possums, pygmy possums, cuscuses, bats, rodents and platypuses and the now extinct diprotodontids, thylacoleonids, ilariids and wynyardiids. In addition to mammals there are crocodiles, snakes, lizards, turtles, lungfish, frogs, birds, snails, insects and other invertebrates.
Some of the most unusual and remarkable animals in the Australian fossil record have been found at Riversleigh. These include 'Thingodonta' (Yalkaparidon), so named because it has a skull and teeth completely unlike any known marsupial and has been assigned to its own family. 'Fangaroo' was a small herbivorous kangaroo with huge canine teeth. Perhaps it used them for defence against predators such as the Giant Rat-kangaroo, Ekaltadeta, a kangaroo that ate meat. Mekosuchus was a goanna-like crocodile that may even have climbed trees. Unlike the modern Platypus, the Riversleigh platypus, Obdurodon dicksoni, had teeth like its Cretaceous ancestors. Although found today only in desert sands, the ancestor of the Marsupial Mole, Notoryctes, has a predeccessor at Riversleigh that might have burrowed through the leaf litter of ancient Tertiary forests. Part Emu and part Cassowary, the Emuary, Emuarius, seems to represent a form near the divergence of these two birds’ lineages.
Although Riversleigh provides a wealth of information about the evolution of the Australian fauna, many mysteries have also been uncovered and are yet to be solved.