The genes of a newfound snake family suggest blind snakes lived on the island of Madagascar since, well, before it was an island.
The discovery is helping to decode how these rarely seen—and barely seeing, though not completely blind—snakes came to colonize much of the planet.
Growing to about a foot (30 centimeters) long, blind snakes act a lot like worms, burrowing under the surface of every continent except Antarctica. Unlike worms, though, blind snakes have backbones and tiny scales.
“Continental drift had a huge impact on blind snake evolution by separating populations from each other as continents moved apart,” said study co-leader Nicolas Vidal, of the Muséum National d’Histoire Naturelle in Paris.
Now considered part of Africa, Madagascar split from what’s now India about 94 million years ago. (Learn about plate tectonics.)
Since then, the blind snakes on Madagascar have changed enough to give rise to a whole new family, added Penn State biologist Blair Hedges, the study’s other co-leader.
(Related: “Biggest Snake Photos: Prehistoric Giant Discovered.”)
Blind Snakes Break Free of “Indigascar”
Blind snake fossils are nearly nonexistent, so their evolutionary history has been a mystery.
But by comparing five genes from 96 far-flung blind snake species, the researchers were able to create a map of the snakes’ evolutionary family tree.
Using estimated time frames for genetic mutation, the team was able to estimate when the different species had arisen.
The wormlike snakes first appeared on the southern supercontinent Gondwana (see a map of Earth during this time), the team says.
As Gondwana split apart, the blind snakes were isolated to what the researchers call Indigascar—a landmass including what are now India and Madagascar.
Relatively soon after the split, the newly recognized family arose, genetic data suggest.
(Related: “Snake Ancestors Lost Limbs on Land, Study Says.”)
Mystery of Blind Snakes’ Spread
After the “Indigascar” split, blind snakes somehow migrated far beyond India and Madagascar.
The snakes mysteriously appeared in Australia some 28 million years ago, for example—a period during which no land connections existed to that continent.
And African and South American blind snake lineages apparently separated only 63 million years ago. That’s some 40 million years after Africa and South America split up, so moving landmasses can’t have caused the later evolutionary divide.
So how did the snakes hop continents?
With continental drift—and of course, flight—ruled out, “you can see that dispersal over ocean waters had to have occurred for these snakes to get to Australia and also to colonize South America and the Caribbean islands,†Hedges said.
In other words, the snakes went rafting, crossing oceans aboard floating vegetation stocked with their insect prey. (Related: “Mammals ‘Rafted’ to Madagascar, Climate Model Suggests.”)
“Some scientists have argued that oceanic dispersal is an unlikely way for burrowing organisms to become distributed around the world,” Hedges said in a statement.
“Our data now reinforce the message that such ‘unlikely’ events nonetheless happened in evolutionary history.”
Findings published March 30 in the journal Biology Letters.
source : http://news.nationalgeographic.com/news/2010/04/100401-blind-snakes-madagascar/