A new species of giant rat has been discovered deep in the jungle of Papua New Guinea.

巴布亚新几内亚丛林深处发现一种新巨鼠。

The rat, which has no fear of humans, measures 82cm long, placing it among the largest species of rat known anywhere in the world.

The creature, which has not yet been formally described, was discovered by an expedition team filming the BBC programme Lost Land of the Volcano.

It is one of a number of exotic（异国的，外来的） animals found by the expedition team.

Like the other exotic species, the rat is believed to live within the Mount Bosavi crater¹, and nowhere else.

"This is one of the world's largest rats. It is a true rat, the same kind you find in the city sewers（下水道）," says Dr Kristofer Helgen, a mammalogist（哺乳动物学） based at the Smithsonian National Museum of Natural History who accompanied the BBC expedition team.

Initially², the giant rat was first captured on film by an infrared³ camera trap, which BBC wildlife cameraman Gordon Buchanan set up in the forest on the slopes of the volcano.

The expedition team from the BBC Natural History Unit recorded the rat rummaging⁴（搜，检查） around on the forest floor, and were awed⁵ by its size.

Immediately, they suspected it could be a species never before recorded by science, but they needed to see a live animal to be sure.

Then trackers accompanying the team managed to trap a live specimen⁶.

"I had a cat and it was about the same size as this rat," says Buchanan.

The trapped rat measured 82cm in length from its nose to its tail, and weighed approximately 1.5kg.

It had a silver-brown coat of thick long fur, which the scientists who examined it believe may help it survive the wet and cold conditions that can occur within the high volcano crater（弹坑，火山口）. The location where the rat was discovered lies at an elevation⁷（海拔，提高） of over 1,000m.

Initial investigations⁸ suggest the rat belongs to the genus Mallomys, which contains a handful of other out-sized species.

It has provisionally（暂时地，临时地） been called the Bosavi woolly rat, while its scientific name has yet to be agreed.

Other rodents（啮齿类）, the group of animals that includes rats, grow to a bigger size.

For example, the largest rodent⁹ of all is the capybara（水豚）, which lives in or near freshwater in South America.

It can grow up to 130cm long and weigh up to 65kg.

The Philippines is also home to a few species of cloud rat which can reach over 2kg in weight.

But of the true rats, which includes urban brown and black rats that belong to the genus Rattus, few can match the new species.

In 2007, an expedition to New Guinea led by Conservation International discovered another closely related giant woolly rat, which can weigh up to 1.4kg. It also belongs within the genus Mallomys.

However, that species lives in the Foja Mountains, part of the Mamberamo Basin.

Mount Bosavi, where the new rat was found, is an extinct volcano that lies deep in the remote Southern Highlands of Papua New Guinea.

The expedition team entered the crater to explore pristine¹¹（原来的，原始的） forest, where few humans have set foot.

Even members of the Kasua tribe, who acted as trackers for the expedition, live outside the crater, which is 4km wide and has walls up to 1km high, trapping the creatures that live within.

The island which includes Papua New Guinea and New Guinea is famous for the number and diversity of the rats and mice that live there.

Over 57 species of true "Murid" rats and mice can be found on the island. The larger rats are often caught by hunters and eaten.

Broadcast of The Lost Land of the Volcano series will begin on BBC One on Tuesday 8 September at 2100 BST. The discovery of the Bosavi woolly rat is broadcast as part of the series on BBC One on Tuesday 22 September.