Lower Cretaceous Amphibians

Australia: The Land Where Time Began

Lower Cretaceous Amphibians

In the Wonthaggi Formation, Victoria, a partial skull, several jaws and a number of postcranial elements have been found of temnospondyl amphibians. Though these bones are rare they are important because they are the youngest known bones of Temnospondyl amphibians in the world, making them a key example of how relict species tended to survive in the cold high-latitude environments of southeast Australia in the Cretaceous. This may have been made possible, as has been suggested, because of the lack of competition from the more advanced forms in warmer parts of the world that would need to evolve special adaptations to migrate into the south polar regions with their extreme climate.

Reaching their peak of diversity during the Triassic temnospondyl amphibians were mostly extinct by about 200 Ma, leaving isolated species from the Jurassic of Australia, central Asia and South Africa. The last known temnospondyl was Koolasuchus cleelandi from the Early Cretaceous of Australia. With a skull length of about 650 mm and an estimated body length of up to 3 m, the last known temnospondyl was a large bodied member of the family Chigutisauridae. During the Late Triassic and Early Jurassic this group was widely distributed across Gondwana, being found in Australia, South America, India and possibly South Africa. Koolasuchus is believed to have lived in inland rivers and preyed mostly on fish, a lifestyle that was adopted by crocodiles after the Aptian. It has been suggested that the warming of the climate at the boundary of the Aptian-Albian was probably the factor that led to the demise of the temnospondyls. Crocodiles were less cold-adapted than temnospondyls, becoming inactive when the temperature dropped below 10^o C, but once the climate warmed sufficiently it is believed they may have outcompeted the cold weather specialised temnospondyls.

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