Riversleigh World Heritage Area
Riversleigh World Heritage Area is Australia's most famous fossil location, recognised for the series of well preserved fossils deposited from the early Miocene to more recent geological periods. The fossiliferous limestone system is located near the Gregory River in the north-west of Queensland, an environment that was once a very wet rainforest that became more arid as the Gondwanan land masses separated and the Australian continent moved north. The 100-km2 area has fossil remains of ancient mammals, birds, and reptiles of the Oligocene and Miocene ages, many of which were discovered and are only known from the Riversleigh area; the species that have occurred there are known as the Riversleigh fauna.
|UNESCO World Heritage Site|
|Location||Gregory, Queensland, Australia|
|Part of||Australian Fossil Mammal Sites (Riversleigh / Naracoorte)|
|Criteria||Natural: (viii), (ix)|
|Inscription||1994 (18th Session)|
|Area||10,029 ha (38.72 sq mi)|
The fossils at Riversleigh are unusual because they are found in soft freshwater limestone which has not been compressed. This means the animal remains retain their three-dimensional structure, rather than being flattened like in most fossil sites. The area is located within the catchment of the Gregory River. Many of the fossil sites were crevices and limstone caves created by the action of large amounts of water on the karst formation, creating pitfall traps and feeding spots for predators which periodically and perhaps suddenly became covered and preserved; these conditions are responsible for the large assemblages of fossilised bats whose guano helped to conserve the remains of themselves and others.
Fossils were first noted to exist in the area in 1901. An initial exploration survey was conducted in 1963. Since 1976, the area has been the subject of systemic exploration. The site was co-listed with the Naracoorte Caves National Park in South Australia as a World Heritage site in 1994, and by itself, it is an extension of the Boodjamulla National Park.
Fossils at Riversleigh are found in limestone by lime-rich freshwater pools, and in caves, when the ecosystem was evolving from rich rainforest to semiarid grassland community. Some of the fossils at Riversleigh are 25 million years old. High concentrations of calcium carbonate have meant the fossils are extremely well preserved. The fossil collection reveals mammalian evolution across more than 20 million years. Fossils have been found in more than 200 individual locations. The fossil record here is significant because it provides evidence on evolution and the distribution of species across Gondwana.
The presence of Riversleigh fauna in the Oligo-Miocene has been classified by four "faunal zones", and used to denote the presence of fossil taxa in these time periods. These may be summarised as
- Faunal Zone A (FZA): late Oligocene, a period 23.03–28.4 million years before present
- Faunal Zone B (FZB): early Miocene, 15.97-23.03 myr
- Faunal Zone C (FZC): middle Miocene, 11.608-15.97 myr
- Faunal Zone D (FZD): late Miocene, 5.332-11.608 myr
The skull and nearly complete dentition of a 15-million-year-old monotreme, Obdurodon dicksoni, provide a window into the evolution of this characteristically Australian group. Fossil ancestors of the recently extinct thylacine, Thylacinus cynocephalus, have also been identified among Riversleigh's fauna. In 1993, Nimbadon skulls were unearthed in a previously unknown cave in the region. Researchers estimate that the prehistoric marsupial first appeared about 15 million years ago and died out about 12 million years ago, perhaps from climate change-induced losses in habitat. A well-preserved skull of the ancient Nimbacinus dicksoni marsupial found at Riversleigh has been used to determine the hunting behavior of the species.
Other fossils have provided evidence of how the koala has evolved in response to Australia's change from predominant rainforest vegetation to drier eucalypt forests. Some fossil insects and plants have also been discovered.
Scientific studies are mostly conducted by a group of palaeontologists from the University of New South Wales. Mike Archer is a paleontologist who has been working at Riversleigh since 1983. He and his co-workers discovered that diluted acetic acid was the most effective method of extracting fossils.
- Archer M; Hand, Suzanne J. & Godthelp H.  2000. Australia's lost world: Riversleigh, World Heritage Site. Reed, Sydney.
- Anna Salleh (16 February 2006). "Huge skulls clues to snake evolution". ABC Science. Australian Broadcasting Corporation. Retrieved 5 August 2010.
- "Australian Fossil Mammal Site - Riversleigh more information". Department of Sustainability, Environment, Water, Population and Communities. 15 May 2008. Retrieved 28 July 2012.
- The Australian Heritage Council (2012). Australia' Fossil Heritage: A Catalogue of Important Australian Fossil Sites. Csiro Publishing. pp. 43–44. ISBN 0643102302. Retrieved 28 July 2012.
- "Australian Fossil Mammal Sites (Riversleigh / Naracoorte)". UNESCO World Heritage Centre. Retrieved 17 May 2015.
- "Riversleigh World Heritage Site, Boodjamulla (Lawn Hill) National Park: Nature, culture and history". Department of Environment and Resource Management. 14 December 2011. Archived from the original on 13 September 2011. Retrieved 28 July 2012.
- "Faunal zones". Faunal encyclopedia. wakaleo.net. Retrieved 28 May 2019.
- "Cave yields marsupial fossil haul". BBC News. 19 July 2010. Retrieved 5 August 2010.
- Fossils reveal prehistoric life cycle[permanent dead link]. Australian Geographic. 20 July 2010.
- Jonathan Marker (10 April 2014). "This meat-eating marsupial may have hunted prey larger than itself". Science Recorder News. Archived from the original on 13 April 2014. Retrieved 11 April 2014.
- Dan Gaffney (19 December 2009). "Loud and lazy but didn't chew gum: Ancient koalas". PhysOrg. PhysOrg.com. Retrieved 5 August 2010.
- Archer, M. et al. 1991. Riversleigh: the Story of Australia's Inland Rainforests, (Sydney: Reed Books).