Location: Queensland, Australia
Age: 25 million years to present
The fossils of Riversleigh are mostly vertebrates, with a few snails and insects. The vertebrates show an amazing diversity and are also found in very large numbers. As the sites are from ages spanning the last 25 million years, they help show an insight in to the evolution of Australia fauna. Australia has a unique fauna found nowhere else in the world today and so Riversleigh can help show how these animals came to be.
The sites show windows into different time periods and so the make up of the fauna changes with each locality. The Late Oligocene (25ma) to Middle Miocene (10ma) sites show the greatest diversity of animals when the area was covered in rainforest. Specialised creatures dominate the fossil fauna as the habitat was very productive so could support these animals well. Animals such as the Forest Koala and Possums lived in the trees eating leaves and fruit. Bandicoots and Thingodonta probably searched for insects on the forest floor whereas the larger marsupials like Nimbadon and the Riversleigh Forest Beast ate shoots. These animals were hunted by the larger carnivores such as the Cleaver-headed Crocodile or the smaller tree climbing Ridge-headed Crocodile. The Thylacine would have chased down smaller animals on the forest floor. Other animals such as the specialised bird of prey, Flexiraptor could hunt in the trees and due to its special jointed feet, could pick out animals from tree hollows. A full food web can be drawn up from the fossils found in this diverse environment.
By the Pliocene (5ma) the climate had changed from rainforest to a more arid environment with grasslands. The Riversleigh Budgerigar lived off the grasslands by eating seeds as it still does today. With the change in climate came a change in the vertebrate population to a less diverse one. By the Pleistocene (1.6ma) animals were not as specialised and so this helped them cope with the less productive environment. Many of the animals were now suited to the open forest environment and grasslands.
The Pleistocene was a time of relatively giant marsupials and other very large creatures. The Giant short-faced Kangaroo, which was up to 3 metres in height grazed the area. The largest marsupial found was also grazing at this time. Diprotodon was 3 metres long and 2 metres high at the shoulder and would have made an ideal meal for the Marsupial Lion. The Lion was the largest meat-eater on the continent and would have lived like present day lions on the savannah. Other animals would have lived in the open forests and possibly sometimes on the grass lands. Megalania was the largest goanna measuring up to 7 metres and weighing in at over half-a-tonne. It would have lived in the open forest eating small animals. Platypus and Koalas lived in similar areas as they do today. Rats were on the menu by this time as they had managed to disperse from Asia. Cave bats and other carnivores would have made use of this new food source.
The Holocene (10ka to present) sites show fossils of Dingos, which invaded or were brought in by humans, around 4,000 years ago. More recent animals to invade such as the red fox and rabbits have not been found in fossil form but as Riversleigh is an on-going lagerstätte, their remains may show up in the future.
Fossils that are less useful in the reconstructing of Australia's faunal relations are also found over the time periods at Riversleigh. Their descendants are still around today and often unchanged such as Snakes, Lizards and Amphibians. Other vertebrates include more Crocodiles, Turtles, Birds and Bats are very much still widely distributed over Australia.
(Click on links for pictures of animals - sorry for the poor quality but I couldn't get copyrights)
Late Oligocene (25ma) to Middle Miocene (10ma):
Cockatoo (Cacatua species
Leaf-nosed Bat (Brachipposideros nooraleebus)
Flexiraptor (Pengana robertbolesi)
Cleaver-headed Crocodile (Baru wickeni)
Ridge-headed Crocodile (Trilophosuchus rackhami)
Thylacine (Nimbacinus dicksoni)
Thingodonta (Yalkaparidon coheni)
Nimbadon (Nimbadon lavarackorum)
Riversleigh Forest Beast (Silvabestius johnnilandi)
Platypus (Obdurodon dicksoni)
Rainforest Koala (Nimiokoala greystanesi)
Sprite Possum (not yet named)
Tube-nosed Bandicoot (Yarala burchfieldi)
Tirari Paljara (Paljara tirarensae)
Wakaleo (Wakaleo vanderleuri)
Pliocene (5 to 1.6ma) :
Budgerigar (Melopsittacus undulatus)
Pleistocene (1.6ma to 10ka):
Megalania (Megalania prisca)
Diprotodon (Diprotodon optatum)
Giant Short-faced Kangaroo (Procoptodon goliah)
Koala (Phascolarctos cinereus)
Platypus (Ornithorhynchus anatinu)
Marsupial Lion (Thylacoleo carnifex)
Holocene (10ka to present):
Dingo (Canis lupus dingo)
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