Australia: The Land Where Time Began

A biography of the Australian continent 

Riversleigh frogs

Hundreds of tree-dwelling and ground-dwelling Oligo-Miocene frogs ave been found in the Riversleigh deposits. The fossil record of frogs in Australia prior to their discovery at Riversleigh was very meagre, being restricted to a few sites, from Quaternary deposits in caves in Western Australia and South Australia, and from the Lake Eyre Basin in South Australia, where a few isolated Tertiary fossil frogs were found.

Mostly complete skeletons have been found in the Upper Site, that includes a large part of an intact skull, many ilia bones, about 1000 ilia-500 frogs, have been recovered. The Riversleigh area is believed to be the richest frog fauna of any fossil frog site in the world, with as many as 20 species found. In these deposits are at least 8 species of hylid tree frogs, from the Genus Litoria. There are 6 species of ground frog (leptodactylid) found.

Among the living frogs the genus Litoria is widespread across Australia, about 50 species being known. The various species come in a wide range of sizes, colours, shapes and behaviours, and they live in a very wide range of habitats. The best known of this genus are the green tree frogs. One of these Australian tree frogs, Litoria infrafrenata, up to 140 mm long, from northern Australia and New Guinea, is thought to be the biggest of its type in the world. A species of tree frog that was even larger has been found in a number of Riversleigh sites such as the GAG Site.

Genera of leptodactylids found at Riversleigh include Limnodynastes, Crinia, Kyarranus and Lechriodus. Living species of Limnodastes are present across the continent. Living Crinia species are found in or near areas of southeast and southwest Australia that are permanently damp.

Living Kyarranus species are found only in the Queensland-New South Wales border area, mostly in cold, wet rainforests at high altitude.

There is only a single living species of Lechriodus, found in coastal rainforests from southern Queensland to northern New South Wales. There are 3 living species known from New Guinea.

The range of habitats of the living frogs related to the Riversleigh frogs give some idea of the wide diversity of frogs and their habitats that once existed in the Riversleigh area. It must have been a veritable paradise for biologists at peak of its existence.

The fact that most of the frog ilia found at Riversleigh are from small species indicates that it had a climate that kept it permanently moist, as the small frogs are the most sensitive to dehydration, requiring a habitat that never dries. Among Australian frogs, the only areas where there is a high proportion of small species are in permanently wet places. In Australia these conditions are rare, being found only in the extreme southwest corner of western Australia and along the northern fringe of Arnhem Land in the Northern Territory.

Frogs are a good indicator of climate because of their sensitivity to drying. Based on the large number and quality of the frog fossils over the time span of the Riversleigh deposits it is possible to use them to track the climatic changes over the 25 million years covered in the deposits. Frogs require a certain, continuous, level of moisture at ground level for their existence, and the various taxa have varying requirements. By studying how the various taxa waxed and waned across time indicates how the environment changed over time.

Sources & Further reading

Michael Archer, Suzanne J. Hand & Henk Godthelp, Australia's Lost World: Riversleigh, world heritage Site, Reed New Holland

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Author: M. H. Monroe
Email:  admin@austhrutime.com
Last Updated 25/02/2011

 

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                                                                                           Author: M.H.Monroe  Email: admin@austhrutime.com     Sources & Further reading