Inaugural Fellows Lecture – Professor Michael Archer AM

“An evolutionary history of Australia”

The Society was proud to have Professor Michael Archer AM present the inaugural Fellows Lecture on Wednesday, 3 April 2013. Professor Archer was one of the first Fellows appointed by the Society, recognising his outstanding work as a palaeontologist, particularly in relation to the Riversleigh fossil find in Queensland, one of the richest fossil deposits in the world.

Until about 50 years ago, only about 70 fossil mammals had been found in the whole Australian continent, compared to about 50,000 in North America. The geology of the Riversleigh area, in northern Queensland, is unusual. There are large expanses of very old (1.6 billion years) Precambrian rock and more recent Cambrian deposits (500 million years old) that contain rather unremarkable fossils of the era. But there are pockets of more recent geological deposits, 10-25 million years old, that have been found to contain extraordinarily well-preserved fossils. There are about 40 sq. km of these deposits. A wide range of unusual animals have been found: five kinds of thylacine, giant, toothed platypus, flesh-eating kangaroos and ancient birds. Some of the birds are the biggest ever discovered and would have weighed up to 400 kg. Also, huge fossilised snakes, importantly, a diverse range of ancient bats and a great variety of trees and plants have been discovered.

How did this extraordinary preservation take place? Professor Archer explained that there were two phenomena that together resulted in this remarkable deposit. Water that percolated up from subterranean deposits were saturated in calcium carbonate and this quickly precipitated around any dead animals that fell into the water. This was responsible for preserving skeletons intact and is easily removed using weak acid such as acetic acid that quickly dissolve the calcium carbonate, exposing a well-preserved fossilised skeleton. But in addition, another phenomenon called ‘bacterially-mediated phosphatisation’, means phosphates from bat droppings have preserved soft tissue, resulting in remarkably complete fossils being found in many areas. In a process known as ‘tufagenic barrage’, calcium carbonate deposits formed dams that allowed fossilisation to take place. These dams were ultimately breached but the fossils were preserved. At the time, Riversleigh area was covered with rainforest but this has gradually receded to coastal zones.

The Riversleigh deposits cover five phases from 25 million years ago to 1.5 million years ago and is the richest sequence in Australia. (There is only one other similar deposit in the world – this is in France.) The Riversleigh find has completely changed perceptions about Australia’s past. It is now clear that there is a diversity in the fossil record suggesting an environment that was as rich at the time as Borneo and the Amazon regions are today. About 15 million years ago Australia started to dry out, yet it was not until about 3 million years ago that extensive grasslands formed.

Professor Archer pointed out that the fossil record gives us a very rich understanding of the way in which current species have evolved from which we can deduce how habitat change can be managed and to protect species that might be at risk of extinction as climate change takes place. We can also gain insight into which species are at threat by understanding the extent to which their populations have increased or declined over long periods of time.