Until now the only known poisonous lizard was the Gila Monster, or beaded lizard, native to the deserts of the southwestern United States and Mexico.

But an international team of scientists led by molecular geneticist Brian Fry of the Australian Venom Research unit at Melbourne University has discovered two more poisonous lizard species -- monitors and iguanas.

Their research, published Thursday in the journal Nature, suggests that the venom systems of snakes and lizards share a common past, rather than having evolved separately as earlier believed.

The lizards do not produce enough venom to be dangerous to humans, but the poison is able to kill small prey, Fry said.

Fry spent months in the Australian desert and tropics capturing, studying and milking dozens of lizards. His team then studied their toxins and DNA.

The discoveries could lead to the development of new medicines based on lizard toxins, Fry said.

"These molecules represent a tremendous, hitherto unexplored resource for utilisation in drug design," Fry was quoted as saying by The Sydney Morning Herald.

He said the venom could be particularly useful in developing drugs for blood pressure and clotting disorders.

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