German researchers have discovered that the oldest known giant salamander Aviturus exsecratus was able to live on land as well as in water.
An artist’s reconstruction of Aviturus exsecratus (Vasilyan D)
Giant salamanders are amazing animals. They can live up to 100 years, grow up to 2 m in length, and have inhabited the Earth for more than 56 million years. The fossils of these amphibians, found relatively often in Eurasia, show little variation from their modern descendants.
Early giant salamanders had a similar lifestyle and were just as big as today’s, which live in East Asia and North America. But while the latter stick to oxygen-rich, fast-flowing mountain streams in China, Japan and the US, their ancestors also lived in rivers and lakes in the lowlands.
The researchers at the University of Tübingen 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 this salamander hunted for food both in the water and on land that makes it different from all the later giant salamanders.
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 paleozoological amphibians such as eryops, which lived 300 million years ago.
By analyzing the shape of Aviturus’ lower jaw, the scientists have found that the salamander fed on fish and invertebrates in the water. 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 findings were published in a paper in the recent issue of the journal PloS-ONE.
The researchers suggest this drastic individual development in Aviturus exsecratus was probably due to a short period of global warming 55.8 million years ago known as the Paleocene-Eocene Thermal Maximum.
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Bibliographic information: Vasilyan D, Böhme M. 2012. Pronounced Peramorphosis in Lissamphibians – Aviturus exsecratus (Urodela, Cryptobranchidae) from the Paleocene–Eocene Thermal Maximum of Mongolia. PLoS ONE 7(9): e40665; doi: 10.1371/journal.pone.0040665
