It has a double penis, is as long as a tall human, and lives in a heavily populated area of the Philippines. Yet somehow the giant lizard Varanus bitatawa has gone undetected by science until now.

Long known to Filipino tribal hunters, the monitor lizard was identified as a new species in 2009 via its DNA, scale pattern, size, and peculiar penis, a new study says.

At about six and a half feet (two meters) long, the new lizard species is closely related to the world's largest living lizard, the Komodo dragon. Unlike the Komodo, though, Varanus bitatawa has evolved to be a vegetarian.

The lizard discovery "comes as an unprecedented surprise," not least because V. bitatawa's home island of Luzon is "heavily populated and highly deforested," the study authors write in Wednesday's issue of the journal Biology Letters.

How the Giant Lizard Hid Out From Science

The researchers suspect the 22-pound (10-kilogram) lizard species escaped scientific detection until now because there've been few reptile surveys of the mountain forests where V. bitatawa lives.

These fruit-eating lizards are also "incredibly secretive," said study team member and biologist Daniel Bennett of Mampam Conservation.

"You could stay in that forest for years and have absolutely no idea that they are there," Bennett said. "They spend all their time high up in trees, more than 20 meters [66 feet] above the ground." Similar lizard species spend less than 20 minutes on the ground per week, he added.

But while scientists weren't aware of the lizard, its existence comes as no surprise to resident tribespeople who hunt the creature for its meat.

Photographs of hunters with the lizard delicacy taken in 2001 spurred the team's two-month expedition in search of the elusive species last summer.

Split Penis Points the Way

The team captured specimens of both V. bitatawa and the extremely rare but closely related Gray's monitor lizard (Varanus olivaceus), another Philippines native.

Capturing both types of lizards was crucial, Bennett said, because it allowed the team to inspect the two monitor lizards side-by-side and detect subtle differences that can help determine whether the animals represent different species.

One particularly revealing trait was the double-ended penis common to monitor lizards. The shape of this reptilian feature is unique to each species.

The giant-lizard find "adds to the recognition of the Philippines as a global conservation hot spot and a regional superpower of biodiversity," the study team says.