Island hopping

Ranid frogs may have originated in India

source: Jeff Hecht
New Scientist April 14 2001 p10

Ranid frogs may have originated in India, and remained there for 60 million years, researchers from the Free University of Brussels believe. Ranid frogs account for a fifth of amphibians world wide. They are thought to have evolved in India some 120 million years ago, at a time when India was an island, so they were unable to reach other land masses. Around 90 million years ago, Madagascar separated from India, and frogs would have been on Madagascar. Some 60 million years ago the Eurasian and Indian plates collided, allowing frogs to spread to the mainland.

The researchers reached these conclusions following a study of DNA sequence differences between different frog species. Such differences can provide a molecular clock, if there are constant rates of genetic change. The clocks allow scientists to tell when divergence of populations occurred. Dating from molecular clocks may differ from dating based on fossil evidence.

Scientists previously thought that frogs spread to India from Africa or Asia. Mammals and birds may also have come from India, which may explain why fossil evidence indicates younger ages than those calculated from molecular clocks. There is no certainty, however, that evidence from frogs can be applied to mammals and birds.