Australia's Mary River Turtle - with its green Mohican-style hair and ability to breathe through its genitals - is one of the world's most distinctive reptiles.

It is also now officially among the most endangered.

The "punk turtle" was this week ranked 29th on the Zoological Society of London's Evolutionary Distinct and Globally Endangered list, triggering calls for better protection of the reptile found in a remote part of Australia's east coast.

"You have to go back about 50 million years to find a closely related species," said Marilyn Connell, a researcher at Australia's Charles Darwin University.

"It would be a failure if we let this animal that walked alongside dinosaurs become extinct."

Once a popular pet in Australia, the exact population of the Mary River Turtle, known to biologists as Elusor macrurus, is unknown, the Zoological Society of London said. Its distinctive hairdo is actually algae that grow on its head.

Academic research was hampered in 1974 when traders refused to reveal the habitat of what were then known as "Penny Turtles" after Australia outlawed the practice of keeping them as pets.

Nearly 20 years later, John Cann, a Sydney-based turtle enthusiast, rediscovered the turtle in the Mary River in Queensland. It was classified as a new species.

The turtle's habitat is not fully protected, Cann said, and the introduction of new fish species to the waterway also threatened juvenile turtles.

"They survived in good numbers for millions of years," Cann said. "Then along came the pigs and foxes, and on top of the native predators and people - that's what has made them endangered."