Near Mount Isa is Riversleigh Station, where the river has cut down and down into its valley, exposing ancient rocks.  This revealed a wealth of fossils, contributing one third of all the known mammal fossils in Queensland, and Mount Isa has a palaeontological research lab for their ongoing processing.

 

The fossils were formed in 3 very specific ways:

 

1)  Large carnivorous cave dwelling bats catch small mammals, and spit out the bits they don’t want on to the cave floor.  Layers of bat guano and small mammal bones accumulate and become compressed and fossilised.  Erosion by the river exposes the cave floor.

 

2) Water seeps into cracks in the rock and acids dissolve out a pit which enlarges and forms a pit trap.  Animals fall in, die, the pit gradually fills with sediment, then erosion exposes the pit floor.

 

3)  Brittle rock crusts over pools are walked on by animals which fall in.  If not eaten by crocs, their remains get buried in the sediment, forming fossils which are exposed by erosion.

 

The most ancient fossils show animals and plants of a tropical forest/swamp, including a carnivorous marsupial kangaroo-like animal and large carnivorous bats.  The most recent ones showed that the area had dried to grassland with rivers and billabongs, and the mammals at this time got massive, eg a bear'-like kjangaroo 12 ft tall.  This was about 20,000 years ago, at the time humans were starting to arrive from Java, to meet animals very different from today’s.

 

Don’t have any fossil pics, so random ones included