Australia: The Land Where Time Began

A biography of the Australian continent 

Riversleigh Lizards

Riversleigh has produced fossils from the major groups of living lizards. The most common lizards and best known are the skinks and dragons. Before the discovery of the Riversleigh fossil sites little was known about the history of these groups in Australia. The Oligocene-Pliocene deposits at Riversleigh have now produced a very diverse lizard fauna that includes skinks, geckos and legless lizards.

The very diverse lizards of Australia are mostly endemic. The bluetongue lizards, Tiliqua, are distinctive as a very large skink. A smalll species of Tiliqua has been found at Riversleigh, T. pusilla, about 15 cm long. It seems to be related to the extant pygmy bluetongue T. adelaidensis. The other skink remains from Riversleigh also show similarities to living skinks. The similarities observed between the extinct and extant lizards of Australia suggest that the evolution of Australian lizards has been more conservative than that of Australian mammals, the lizards changing more slowly over time.

The Riversleigh deposits have produced the first known legless lizard fossils from the Tertiary of Australia. These legless have usually been assigned to their own fanily, the Pygopodidae, but based on the results of recent studies it has been suggested that they should probably be re-assigned as specialised legless geckos.

The only fossil Australian dragon was an agamid lizard similar to some species of bearded dragons, Amphibolurus. Many agamid remains have been found at Riversleigh from the Oligocene-Miocene. Most of these have been assigned ot the genus of water dragons Physignathus. Some show similarities otthe living Australian Eastern Water Dragon (P. lesueurii), but most have been assigned to other species of Physignathus, either Physignathus sp. nov. or Physignathus sp. cf. P. lesueurii. The discovery of Physignathus species at Riversleigh confirms other evidence that the climate at Riversleigh was once much wetter than now, as no species of this genus has been found so far from the coast. Another species of agamid has been found, Sulcatidens quadratus, the highly distinctive teeth of which have caused a problem sorting out its relationship to other agamids.

Among living agamids it has been found that in wetter areas they are less diverse than in drier areas. The agamid finds from Riversleigh has shown the same diversity pattern. More confirmation of the wet climate prevailing, as well as demonstrating that the pattern of agamid diversity was already established at the time of the Riversleigh deposits. Apparent ecological differences have also been noted between the agamid assemblages from Riversleigh and those of living agamids. At Riversleigh there was a very diverse crocodilian population and large numbers of water dragons, but at the present there are only 2 species of crocodile in the north of Australia, and crocodiles and water dragons share a habitat at only one place in the far north of the range of the Eastern Water Dragon.

Sources & Further reading

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

 

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