Sept. 22, 2005 — Fossil salamanders unearthed in Yellowstone National Park have kept a record of the effects of climate change over the past 3,000 years, according to a large-scale study of the amphibian remains.

Elizabeth Hadly of Stanford University in California, and colleagues report in the current issue of the journal BMC Ecology that salamanders have grown bigger as the climate has warmed and may continue to increase their size.

Hadly collected and examined 2,850 fossilized tiger salamanders (Ambystoma tigrinum) from 15 layers in Lamar Cave, an exceptionally rich paleontological site in Wyoming's Yellowstone National Park.

Tiger salamanders have a complex life cycle that involves both land and water. These amphibians can become terrestrial adults or be paedomorphic — sexually mature, yet remaining in the water and keeping some characteristics of a young animal, like gills.

"Ambystoma tigrinum is unusual in that it retains the ability to metamorphose facultatively even after years in the aquatic form," said the researchers.

They dated and divided Yellowstone's cave deposits into five time periods corresponding to different climates over the past 3,000 years.

The fossils were then put into four groups: young larval, paedomorphic, young terrestrial and old terrestrial. Lastly, Hadly and her team measured the fossils' body sizes in each group and time period.

"We found a significant difference in the body size of the paedomorphic and terrestrial adults within the Medieval Warm Period (the warmest period of Yellowstone's history, between 1,150 and 650 years ago). Terrestrial adults were much larger than the paedomorphic individuals," Hadly told Animal Planet News.

Land salamanders would have grown bigger as a response to warm and dry climate conditions, which allowed for more abundant food.

However, the researchers found no difference in the number of water and land salamanders at that time, suggesting that the warm climate did not influence the amphibians' decision to go onto land.

"This demonstrates that species will respond to climatic change in ways we are not always able to anticipate," Hadly said.

Hadly theorized that tiger salamanders and may grow even bigger under the effects of global warming.

"Modern tiger salamanders, like other ectotherms, are indeterminate growers and we predict that persistent warm climatic conditions would favor continued growth of terrestrial adults," she said.

According to Randal Voss, associate professor at the University of Kentucky's department of biology, the study's most interesting result is that land and water salamanders remained in Yellowstone, even though there have been changes in climate and body size.

"This suggests that biodiversity would be maintained in the species in the face of moderate changes in climate. However, if the climate were to change dramatically, as some predict for Yellowstone in the future, that there were no relatively permanent aquatic habitats for paedomorphic salamanders to reach maturity, then we may no longer observe these unique and curious forms," Voss told Animal Planet News.