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In the distant past, climate change may have driven limbless lizards to evolve legs 鈥� having already lost them once before.

The once-four-legged, ancient lizards of the Brachymeles genus first emerged in a dry environment in modern-day South-East Asia. They dropped all four limbs about 62 million years ago, but around 40 million years later, some species聽grew them back, says Philip Bergmann at Clark University in Worcester, Massachusetts.

鈥淎round the time that these lizards went from snake-like to re-evolving limbs, there was this climate shift from an environment that鈥檚 much drier than it is today, to this ever-wet monsoonal climate where you essentially have rainfall all year round,鈥� says Bergmann. Growing limbs back probably helped these burrowing animals dig into the wetter, more packed ground, he says.

Modern Brachymeles skinks (not to be confused with snakes) include species ranging from no limbs, to small limbs with one or two digits, to full limbs with five fingers and five toes. The 鈥渟nake-like鈥� forms are longer with more vertebrae, but the species that re-evolved limbs also lost some of those vertebrae, becoming shorter.

Bergmann and his colleagues captured and carried out precise measurements on nearly 150 wild lizards representing 13 different species of modern Brachymeles in the Philippines and Thailand. They then subjected them to various running and burrowing tests over different soils.

They found that the more snake-like the lizards were, the less force they used to push into the soil with their heads, which were narrower. By contrast, legged lizards dug into the soil with their limbs, using greater force 鈥� an ability that probably helps them live in wetter environments where soil has four times greater resistance compared with dry, loose soil.

Whether Brachymeles will change body forms once more as the climate changes again is yet to be seen, says Bergmann. But given the tens of thousands of years required for such a drastic evolutionary change as limb loss, it is more likely that they will either need to find other ways to adapt to global warming or just fail and go extinct, he says.