A mother lode of fossil salamanders, so well preserved that they almost might have frolicked in last year's mud, is giving scientists a new benchmark for identifying possible ancestors of the amphibians. The 150-million-year-old trove includes the oldest known complete salamander skeletons--near dead ringers for those living today. "To suddenly have hundreds of specimens of very primitive salamanders is very exciting," says paleontologist Robert Carroll of McGill University in Montreal, Canada.
The fossils came to light in 1997 in Hebei Province, China. Working at a site near the town of Fengshan, paleontologist Keqin Gao of the American Museum of Natural History in New York City unearthed more than 500 salamander skeletons in a small quarry. Like the spectacularly fossilized creatures in Liaoning Province (Science, 12 January, p. 232), the salamanders died when a volcano erupted and preserved them in ash. For some, the ash even recorded the impressions of gills. The Fengshan site doesn't contain the great diversity of life preserved in the Liaoning fossil beds, but it does offer a great deal of information about early salamanders.
There were enough fossils to reconstruct all stages of the salamanders' life histories. In the 29 March issue of Nature, Gao and his co-author Neil Shubin of the University of Chicago describe larval and adult forms of two salamander species. One of these, Laccotriton subsolanus, went through a full metamorphosis during its life. The other, Sinerpeton fengshanensis, grew to sexual maturity but never reached metamorphosis, a condition called neoteny. Neoteny has led to much of modern salamander diversity; it's present in nine families. The Fengshan fossils demonstrate that this life history pattern already existed by the Late Jurassic.
It's not surprising to find essentially modern salamanders that long ago, Carroll says. A similarly modern and relatively complete salamander, dating back to the Lower Cretaceous, about 116 million years ago, was previously found in Spain. But he notes that the new fossils will be useful to compare with possible salamander ancestors in the Paleozoic--at least 100 million years older than the Chinese fossils.