"There was nothing developed of telling the story of where the salamander originated," said Keqin Gao of the American Museum of Natural History in New York, New York, and co-author of a paper on the find in the March 29 issue of Nature. "The fossil record was really poor."

Asian Origin

The 150 million-year-old fossils from China extend the fossil record back 85 million years from the previous record. The abundance and diversity of the fossils give scientists a detailed look at the life cycle and evolutionary strategies of the amphibians.

Immediately apparent is the fact that salamanders at that time—the Jurassic period—differed very little from their modern equivalents. The well-documented diversification and variation among salamanders occurred around a body plan that has remained the same for millions of years, according to the researcher.

"For the last 150 million years not much has changed," said Gao.

Diversity among the salamander species was present 150 million years ago. The fossils show that some species underwent complete metamorphosis from tadpole to landlubber and others were neotenic: they matured and reproduced while still in the tadpole stage, like the modern axolotl.

The similarity in diversity among the primitive salamanders of today and the fossils from China leads Gao and colleague Neil Shubin of the University of Chicago to argue that the modern salamanders originated in Asia before they spread to Europe and North America.

Contentious Ancestry

The salamander fossils may also shed light on the contentious debate over what creature gave rise to the salamanders, said Robert Carroll, a zoology professor at McGill University in Montreal, Canada, who wrote an accompanying perspective in Nature.

"It is generally thought that frogs, salamanders, and caecilians [legless and tailless amphibians] came from a single common ancestor," said Carroll. "Beyond that there are very diverse views of what that common ancestor might have been."

An important step in resolving the debate is a solid understanding of the specific ancestry of each amphibian. The detail of the 150 million-year-old salamander fossils from China will enable scientists to compare them with putative salamander ancestors from the Paleozoic, he said.

Gao's research is supported by the National Geographic Society.