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The ´óÏó´«Ã½'s Natural History Unit has discovered a new species of giant rat on an expedition to a remote rainforest in Papua New Guinea. Weighing in at 1.5kg, and measuring 82cm from nose to tail, the Bosavi Woolly Rat is one of the biggest rats in the world – as big as a domestic cat.

The find was made in the crater of the extinct volcano Mount Bosavi while filming for the Lost Land Of The Volcano, the third in a series of ´óÏó´«Ã½ One expeditions to remote jungles.

The team, led by climber and naturalist Steve Backshall, wildlife cameraman Gordon Buchanan and head scientist Dr George McGavin, explore little-known and unprotected parts of rainforest searching for new and barely known wildlife.

The crater is 4km wide with walls up to 1km high, trapping the creatures inside a lost world.

The rat is silvery grey and the name woolly is due to its dense fur. The animal's teeth suggest it has a largely vegetarian diet and probably builds nests in either tree hollows or underground.

Dr Kristofer Helgen, Smithsonian biologist, and Gordon Buchanan, were first on the scene, when the rat was found by a tracker from the Kasua tribe that lives outside the crater.

Dr Helgen says: "This is the one of the world's largest rats. It is a true rat, related to the same kind you find in the city sewers, but a heck of a lot bigger.''

Gordon says: "I had a cat and it was about the same size of this rat. This rat was incredibly tame. It just sat next to me nibbling on a piece of leaf. It won't have seen a human being before. This crater of Mount Bosavi really is the lost world."

Papua New Guinea is famous for the number and diversity of the rats and mice that inhabit the island. More than 57 species of true "Murid" rats and mice can be found on the tropical island.

The giant rat is not the only discovery made by the expedition team. They also found another unique type of mammal called the Bosavi Silky Cuscus.

The animal – which looks like a small bear – is a marsupial that lives up trees, feeding on fruits and leaves. Weighing in at over 2kg, it has dense silky fur adapted for a mountain environment.

Dr Helgen has identified it as a new subspecies in a group of strange marsupials known as cuscuses, saying: "Long ago, it was isolated on this volcano and has become something unique to Bosavi. I travel the world looking for mammals in many different places, but to find something of this size for the first time is a cause for major celebration."

Steve Backshall, who led the team into the crater and held the cuscus in his arms, says: "I can't even begin to say how it feels to have in my hand an animal that has never been seen before."

Like the giant rat, the Bosavi Silky Cuscus also appeared to have no fear of man, suggesting these animals have never come into contact with humans before.

This scientific expedition also found approximately 40 other new species, which are at various stages of being verified. These include a camouflaged gecko, a fanged frog and a fish called the Henamo Grunter – named because it makes grunting noises from its swim bladder.

The expedition base camp was in the foothills east of Mount Bosavi, with smaller teams going to remote locations – one team into the crater and one onto the summit of the mountain. The habitat is currently pristine but, 30km to the south of Mount Bosavi, there are extensive logging operations.

Mount Bosavi was chosen because the fauna of that region is poorly known. The height of the mountain (rising up to 2,700 metres) meant there was a range of habitats from lowland rainforest to montane moss forest. The mountain acts like an island in a sea of jungle, trapping species on it.

Lost Land Of The Volcano (3 x 60-minutes), starts Tuesday 8 September 2009 at 9.00pm on ´óÏó´«Ã½ One.

Notes to Editors

1. The science team was lead by insect specialist Dr George McGavin (University of Oxford) who is a regular presenter on The One Show. Other scientists include mammalogist, Muse Opiang (PNG Institute of Biological Research); bat expert, Alanna Maltby (Zoological Society of London); Dr Kristofer Helgen (Smithsonian Institution); bird scientist, Dr Jack Dumbacher (California Academy of Sciences); fish expert, Dr Phil Willink (Chicago Museum); and frog expert, Allen Allison (Bishop Museum, Hawaii). They worked closely with a team of trackers from the Kasua tribe who own the land and crater.

2. All the animals found go through an independent peer-reviewed process. It is currently estimated that along with the new species of giant rat and cuscus, the expedition found approximately 16 species of frogs, one species of gecko, a minimum of three species of fish, at least 20 species of insects and spiders and possibly one new species of bat.

3. The team was based at Mount Bosavi from the end of January to early March 2009.

4. Lost Land of the Volcano follows on from Expedition Borneo (2007) and Lost Land Of The Jaguar, an expedition to Guyana in South America (2008), which won an RTS Award and was nominated for a BAFTA.

5. Lost Land Of The Volcano is a ´óÏó´«Ã½ Production in partnership with Discovery and ´óÏó´«Ã½ Worldwide. Tim Martin is the executive producer and Steve Greenwood is the series producer.

LK