The fossilized skeleton of a newly discovered amphibian that lived in seawater. Credit: Ryosuke Motani
Amphibians may have lived exclusively in the sea as early as 237 million years ago, according to a study published today in Nature Ecology & Evolution1. The conclusion is based on two exceptionally well-preserved fossils from what is now Guizhou province in China.
The fossils belong to temnospondyls, a primitive group of amphibians that lived during the late Triassic period. The researchers have tentatively named the species Gerrothorax maritimus. The animal was about 74 centimetres long, had a flattened body and was almost completely covered in protective armor.
More than 8,000 amphibian species live today, but none is known to inhabit marine environments exclusively. Steve Brusatte, a paleontologist and evolutionary biologist at the University of Edinburgh in the UK, called the finding “a potentially revolutionary discovery.” He said the Triassic amphibian “was really completely oceanic, so that’s a game changer.”
Schematic diagram of the amphibian skeleton. Credit: Diao, L. Nature Ecology & Evolution
Evidence of a marine lifestyle
Amphibians vary in their tolerance of salt, says study co-author Ryosuke Motani, a paleontologist at the University of California, Davis. Even salt-tolerant animals, however, need a way to remove excess salt. “Most of the time they do it by drinking fresh water,” he explains.
The researchers argue that this was not an option for G. maritimus. The fossils were found far from any land that existed at the time, and the skeletons are so well preserved that the animals do not appear to have been washed out to sea by water. The team also analyzed strontium isotopes, forms of the element that can help identify the geological and aquatic environments in which minerals formed.
Strontium levels in the ancient animal’s bones match those of seawater from the same period. This suggests that G. maritimus “fed on seawater,” the researchers wrote in their paper.
Source: www.nature.com