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Frog Discovery Is "Once in a Century"

John Roach
for National Geographic News
October 15, 2003
 
A frog species whose ancestors evolved in the shadow of dinosaurs has been discovered burrowing into the remote mountains of southern India, a pair of biologists report in the October 16 issue of Nature.

The blackish-purple living fossil looks like a bloated doughnut with stubby legs and a pointy snout. Its closest relatives hang out in the Seychelles, a group of islands 1,900 miles (3,000 kilometers) away.


"We had no idea it would be the closest relative of these Seychelles frogs," said Franky Bossuyt, a biologist at Free University of Brussels in Belgium, who described the species with his colleague S. D. Biju.

Biju and Bossuyt named the new species Nasikabatrachus sahyadrensis and say it is so unique that it warrants the establishment of a new frog family, Nasikabatrachidae, of which it is the only member.

The relationship of Nasikabatrachus with the Sooglossidae in the Seychelles suggests that these frogs evolved about 130 million years ago before an ancient landmass known as Gondwana broke apart, sending India on a collision course with Asia and splitting the Seychelles adrift in the Indian Ocean.

Blair Hedges, an evolutionary biologist at Pennsylvania State University in University Park who wrote an accompanying News and Views on Nasikabatrachus for Nature, said this discovery is remarkable and unique.

"New species are found all the time—about 70 are found each year—but almost always they are related to other known species," he said. "This one is not; it is not closely related to anything and distantly related to a family in the Seychelles. That makes it very remarkable."

There are only 29 families of frogs, encompassing approximately 4,800 known species, and almost all were discovered in the 18th and 19th centuries. This makes the discovery of Nasikabatrachus a once-in-a-century find, added Hedges.

Isolated Mountains

Nasikabatrachus was discovered in the Western Ghats, a mountain range in southern India covered in tropical forests. Conservationists consider it a biodiversity hotspot, a rich but threatened reservoir of unique plant and animal life.

Human pressure, primarily from agriculture, has reduced forest coverage there to less than 10 percent of its original extent, said Hedges. What does remain is remote and inaccessible, which may explain why Nasikabatrachus went undiscovered for so long.

"To go out and search for these things is not easy," said Hedges, who added that as demonstrated by this discovery, it is still worth going out to look around.

Bossuyt said that other people may have seen Nasikabatrachus before, but none had bothered to examine it. Also, "this frog lives underground and it only comes out during the monsoon, about just two weeks per year, and then it is gone again," he said.

Frogs and Continents

Biju and Bossuyt conclude in Nature that the discovery of Nasikabatrachus and its relationship to sooglossids in the Seychelles helps paint a picture of how frogs evolved and spread around the world.

Scientists believe that the breakup and drift of continents influenced the evolution of advanced frogs. For example, India was once part of a large super-continent in the southern hemisphere known as Gondwana, along with South America, Africa, Madagascar, the Seychelles, Antarctica, and Australia.

According to one theory, the chunk that went on to form South America and Africa split from Gondwana about 160 million years ago. The Antarctica-Australia chunk split about 130 million years ago, followed by Madagascar about 90 million years ago and the Seychelles about 65 million years ago.

If this theory is correct, said Hedges, India would have continued on a northward trek isolated from the rest of the world for about 10 million years before it slammed into Asia 55 million years ago and formed the Himalaya.

On one hand, Hedges said "the fact that the new frog is related to something from the southern hemisphere is neat: it shows this geological connection."

On the other hand, Nasikabatrachus is so unique—so different from other frogs and only distantly related to the frogs in the Seychelles—that it supports the theory that India was isolated for millions of years before it rammed Asia, said Hedges.

This theory is contradicted by the fossil record, which shows closely related dinosaurs, lizards, frogs, and mammals in South America, Africa, and Asia. New models have been proposed that incorporate land bridges between these landmasses to explain the fossil record.

"When we find unique organisms it indicates they've been isolated for a lot of time like the giant Galápagos tortoises," said Hedges. "Having a unique frog in India [suggests India was] isolated a fairly long time and supports the model that India didn't have a firm connection with other continents."

The question remains, however, of why the fossil record of India indicates past land connections. "Perhaps those bridges were more like chains of islands that allowed some—but not all—groups to disperse," Hedges concludes in Nature.
 

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