20 million years ago - Australia's splendid isolation
About Riversleigh
Riversleigh is located in north-western Queensland and has more than 250 fossil-rich sites that date from 25 million to 40 000 years ago. From these, thousands of well-preserved fossils have been found and hundreds of new species have been described. It is one of the worlds richest, most detailed and most continuous fossil records of the changes in the animals, habitat and climate of a single area.
Such a rich fossil history has enhanced our understanding of the origins, evolutionary history and diversity of many of Australia's monotreme, marsupial and placental mammal groups. The fossil bat record, with more than 40 species, is one of the richest in the world. Riversleigh also records the history of crocodiles, snakes, lizards, turtles, lungfish, frogs, birds, snails, insects and other invertebrates.
Significant fossils from Riversleigh
One important find at Riversleigh was the 15 million-year-old platypus Obdurodon dicksoni which is known from a skull complete with teeth. This fossil provides new informationrmation about the evolutionary history of this group, the egg-laying mammals.
Some unusual and completely new kinds of animals have been discovered at Riversleigh. One, Yalkaparidon is nicknamed 'Thingodonta' because its skull and teeth are completely unlike any other type of marsupial known. Another is called 'Fangaroo' because it is a small kangaroo with huge canine teeth. But it didn't eat meat - it may have used its fangs as a defence against predators. There was, however, a real meat-eating rat-kangaroo - Ekaltadeta ima.
The unique teeth and skull of Yalkaparidon (left) earned it the nickname 'Thingodonta'. Even though it was a herbivore, 'Fangaroo' (right) had huge canine teeth, which it may have used for defence in the same way as the pygmy deers of modern rainforests.
Photos: S Humphreys © Australian Museum.
Fossil-hunting at Riversleigh
Fossils at Riversleigh are preserved in very hard limestone. This makes it difficult to extract fossils from the rock on site. Instead the rocks are removed and helicopters are used to transport them across the inaccessible terrain to a pick-up point. From there, they are transported to the lab at the University of New South Wales. Here the rocks are soaked in weak acetic acid to dissolve away the limestone, revealing the fossils.
Every year there is an expedition to Riversleigh and new sites are regularly found. Because the sites cover such a range of time and the fossils found are so amazing, Riversleigh was inscribed (with Naracoorte Caves) on the World Heritage list of fossil sites in 1994.
Palaeontologists excavate the Riversleigh limestone (left) before transporting it across inacessible terrain by helicopter (right).
Photos: A Gillespie.
