Frogamander 290 million year old fossil evidence of amphibian ancestry and evolution

10 June 2008

Scientists have discovered a 290 million-year-old fossil "frogamander," that links modern frogs and salamanders. It is believed that the new discovery may resolve a longstanding debate about amphibian ancestry. According to a group of Canadian scientists modern amphibians -- frogs, salamanders and earthworm-like caecilians -- have been a bit slippery about divulging their evolutionary ancestry. It is claimed that gaps in the fossil record showing the transformation of one form into another have led to a lot of scientific debate. The fossil Gerobatrachus hottoni or elderly frog, described in the journal Nature, may help set the record straight.

According to Jason Anderson of the University of Calgary, who led the study, the fossil Gerobatrachus hottoni iis a missing link that falls right between where the fossil record of the extinct form and the fossil record for the modern form begins. "It's a perfect little frogamander," he said.

The Gerobatrachus hottoni fossil has a mixture of frog and salamander features, with fused ankle bones as seen only in salamanders, a wide, frog-like skull, and a backbone that resembles a mix of the two. Based on the study the scientists concluded that modern amphibians would have come from two groups. They say that frogs and salamanders have come from an ancient amphibian known as a temnospondyl. It is also said that worm-like caecilians have more similarity with lepospondyls, which is another group of ancient amphibians.

Anderson said that Frogs and salamanders share a common ancestor that is fairly removed from the origin of caecilians. Gerobatrachus hottoni was discovered in Texas in 1995 by a group from the Smithsonian Institution. It is named after the late Nicholas Hotton, who was a member of that group. Anderson's team painstakingly removed layers of rock to reveal the anatomy of the skeleton.