Washington: Modern giant salamanders adapted to live in water due to global warming, but their ancestors ventured out on land, a new study has found.
According to geoscientists at the University of Tubingen the oldest known giant salamander, aviturus exsecratus, was able to live on land as well as in water.
In the light of recent information, the researchers re-examined fossils of aviturus exsecratus, which lived some 56 million years ago in what is now southern Mongolia.
They were able to demonstrate that the animal hunted for food both in the water and on land. That makes it different from all the later giant salamanders, which live or lived only in water.
The development of a species from a purely aquatic lifestyle to an amphibious-terrestrial lifestyle is linked with gigantism and sustained growth and is called peramorphosis. It is completely unknown in modern salamanders.
Individual development like that was only seen in palaeozoological amphibians such as eryops, which lived 300 million years ago.
The scientists suspect that aviturus exsecratus lived on fish and invertebrates in the water -- as suggested by the shape of its lower jaw. At the same time, aviturus probably hunted insects.
Terrestrial adaptation is indicated by the animal`s heavy bones, long hind legs, a well-developed sense of smell, and palatal dentition typical of a terrestrial salamander.
Also, fossil remains of this huge, up to 2m long animal were found in rock typically formed from water`s-edge sediments.
The researchers think this drastic individual development in aviturus exsecratus was probably due to a short period of global warming 55.8 million years ago.
This most sudden climate change since the death of the dinosaurs saw global temperatures rise 6 degrees Celsius within around 20,000 years.
Professor Dr Madelaine Bohme from the University of T?bingen and Dr Davit Vasilyan of the Terrestrial Palaeoclimatology working group led the study.
These findings are published in the journal `PLOS ONE`.