Washington, June 10 (IANS): Giving an insight into when continents were connected, a study by an Indian-American reveals that the isthmus of Panama, the land connecting North and South America, was formed much earlier than previously thought.

Geologists for long thought that the event, which dramatically changed the world, took place 3.5 million years ago.

But the new research shows that plants and animals had been migrating between the continents nearly 30 million years earlier.

"This means the best-dated geological event we ever had is wrong," said Prosanta Chakrabarty, associate professor, department of biological sciences and curator of ichthyology, Louisiana State University.

Chakrabarty is currently studying the evolution and migration of freshwater fish between South America, Central America and the Greater Antilles that may have began 50 to 60 million years ago.

These migrations imply that geological changes in Central America, such as landmass formation and new freshwater corridors, were aiding migration for many kinds of plants and animals.

"Now we know that the closure of the isthmus of Panama, which is supposed to be one of the biggest deals in geology, is just one part of a really complicated puzzle of how the continents came together," Chakrabarty said.

Chakrabarty and colleagues mapped the evolution of two major families of fishes in Central America -- Cichlids, which include many aquarium fish, and poeciliids, which include guppies and swordtails.

Since freshwater fish can only migrate when a new passage way opens to a river or lake, there must have been dry land with freshwater running through it.”

Therefore, their arrival in Central America signifies early geological changes.

The study appeared in the Proceedings of the National Academy of Sciences.