University of Exeter

A cold-adapted Liolaemus belli lizard is shown here in the Andes near Farellones, Chile. Global warming threatens these species with extinction, according to a new study.

Dozens of lizards that evolved the ability to give birth to live young in order to carve a niche for themselves in colder climates may become extinct as the planet warms over the next 50 years, according to new research.

Since these lizards’ South American habitats are shrinking, the reptiles are forced to move up into the colder climes of the Andes, or down towards the South Pole. But as everything gets warmer overall, the lizards will find natural competition with warm-adapted reptiles who are expanding into these same areas. As a result, multiple extinctions could occur, says David Hodgson, an ecologist at the University of Exeter in England.

The adaptation of live birth (viviparity) helped Liolaemus lizards such as the jewel lizard and the Chilean tree iguana find a niche in cooler spots that are less hospitable to more competitive lizards, ones that lay eggs (oviparity).

Live birth "probably helps to cope with the effects of cold, or unpredictable, conditions on egg survival and embryo development," Hodgson explained in an email to NBC News.

He and colleagues conducted research that indicates once lizards evolve viviparity, the process is irreversible, which appears to restrict them to cold climates.

Why, exactly, viviparous reproduction constrains Liolaemus lizards to cold climates is uncertain, Hodgson noted, but it is possible that they are unable to compete with egg-laying lizards in warmer climates.

Hodgson noted that viviparity exists in other lizard species that live on tropical islands elsewhere around the world, which suggests that climate alone is not a limiting factor in the survival of viviparous reptiles.

"It would appear that viviparity is 'forced out' of warmer climates in South America by the more competitive oviparious species," he said. "But that is speculation."

Hodgson and colleagues concluded March 5 in the journal Global Ecology and Biogeography that "viviparity has been largely responsible for the successful radiation of Liolaemus into cold climates, but ... (it) may prove to be an evolutionary dead-end for lizards facing rapid climate change."

John Roach is a contributing writer for NBC News. To learn more about him, check out his website.