New study reverses theory of chameleons' origins
A new study of 174 species may end the debate regarding the reptile's origin
Agence France-Presse in Paris
Chameleons took to the waves to migrate from Africa to Madagascar about 65 million years ago, said a study published last week that seeks to resolve a roiling biological debate.
The vast majority of the 195 chameleon species today are found in Africa and Madagascar, both once part of a supercontinent called Gondwana, which broke apart some 120 million years ago. The split led the African continent and the island of Madagascar to become separated by a sea trough that today is 400 kilometres wide.
Fossil evidence suggests the first chameleons only showed up after the break-up - but scientists have long disagreed about where.
The new study, based on a genetic analysis of 174 chameleon species, says the migration came from Africa.
It was led by lizard pioneers who probably hitched a ride on rafts of floating debris washed downstream in big African rivers during floods, suggested its authors.
"What we did was estimate the time period when various related chameleons on Africa and Madagascar diverged," said lead author Krystal Tolley at the South African National Biodiversity Institute in Cape Town.
"We found out this was probably first in the late Cretaceous, 65 million years ago, and then again in the Oligocene period, about 45 million years ago," Tolley said. "We concluded that [both dispersal events were] more likely to be from Africa to Madagascar but we then also backed this up by using information on the direction of oceanic currents in those same periods."
During the late Cretaceous and the Oligocene, currents actually flowed from Africa towards Madagascar, the opposite of today's flow.
Another big study on chameleon origins, published in 2002, had concluded the lizards originated in Madagascar.
Ancestral lizards crossed the present-day Mozambique Channel to Africa, where they underwent species differentiation, evolving in habitat niches shaped by climate and landscape change, the authors of that study had said.
"[We] were a bit suspicious of this line of thought, and decided to investigate their origins more closely," said Tolley of the Madagascar-to-Africa theory.
Elsewhere in the Indian Ocean, chameleons had travelled from Africa to the Seychelles Islands on one occasion, and in the Atlantic they managed to make it to Bioko Island in the Gulf of Guinea, said Tolley.