Scientists think that they may have discovered the smallest reptile on the planet – a nano-chameleon.

Two of the tiny lizards were discovered in a joint German and Madagascan expedition in Madagascar.

The male Brookesia nana, or nano-chameleon, has a body of just 13.5mm.

This makes it the smallest of about 11,500 known species of reptiles, according to the Bavarian State collection of Zoology in Munich.

Its length from top to tail is 22mm. The female is far bigger at around 29mm, the institute said, adding that other specimens were yet to be located, despite "great effort".

"The new chameleon is only known from a degraded montane rainforest in northern Madagascar and might be threatened by extinction," said the Scientific Reports journal.

The reptile’s habitat has been subject to deforestation, but the area was recently placed under protection, meaning that the species will survive.

Researchers found that it hunts for mites on the rainforest floor and hides from predators at night in blades of grass.

In a blog post, Dr Mark Scherz, one of the researchers involved in the discovery, called it "a spectacular case of extreme miniaturisation".

The forests where the Brookesia were located are still well connected with others across the north of the island, he said.

"So this tiny new chameleon violates the pattern of the smallest species being found on small islands. That suggests that something else is allowing/causing these chameleons to miniaturise," he added.

In their report, scientists recommended that the chameleon be listed as critically endangered in the International Union for Conservation of Nature's (IUCN) Red List of Threatened Species to help protect it and its habitat.