Indiana McGavin and the giant rat

For six months George McGavin told nobody about the extraordinary creature. “Not my wife, my family or friends,” says the former lecturer turned adventurer. “They would say, ‘It’s got four legs? And fur?’ I said, ‘I’m not saying anything’.”

Not till last week, anyway, when it emerged that McGavin had been up close to a hitherto undiscovered giant rat — the most amazing of dozens of discoveries made on a journey to one of the most remote spots on earth. “The minute we saw it,” says McGavin, “we thought: oh my God, a rat as big as a cat!”

Sherlock Holmes devotees will be reminded of the detective’s tantalising reference to “the giant rat of Sumatra, a story for which the world is not yet prepared”. Well, get ready to hear about the giant rat of Bosavi, encountered on McGavin’s expedition to Papua New Guinea in January. It measures 32in from nose to tail, weighs 3lb, has dense fur and appears to follow a largely vegetarian diet — perhaps just as well for McGavin.

The rat was not the only freakish beast they encountered. The adventurers found about 40 species unknown to science, including fish that make grunting noises, a fanged frog, a new sub-species of a massive mole-looking beast called a cuscus, talking beetles and a five-footed brontosaurus (okay, I made one of those up).

They travelled to Mount Bosavi in Papua New Guinea’s southern highlands and stayed for six weeks. The extinct volcano rises 8,500ft above the lowland forest and forms an enclosed island of assorted microclimates, each crammed with unnamed life forms.

“The high peaks are isolated, so evolution goes at a steady pace,” says McGavin. “You get things that may look superficially the same as others elsewhere but in time will become a new species.”

The speed at which subspecies evolve into entirely new species varies according to how fast an animal breeds: “Insects breed so fast it could be a few hundred years.”

The last eruption of Mount Bosavi was about 225,000 years ago — plenty of time for familiar species to have become unfamiliar ones.

The expedition is the third in as many years for McGavin, who remains a research associate at Jesus College, Oxford, and was assistant curator of entomology at the university’s museum of natural history. With backing from the BBC and the Discovery Channel, he has travelled to Borneo and Guyana with teams of scientists from all over the world eager to manhandle things with supersized whiskers, bonkers feathers and boggly eyes.

McGavin gave up his Oxford career last year on the spur of the moment: “I was cycling home and I had one of those ‘why am I here?’ moments. My life is about education and enthusing people about the natural world. Well, if I had a tutorial at Oxford I had an audience of four people who were already committed. On a cruise ship I might have 400 people. But on telly I have 4m.”

More than 300 hours of footage were edited to make the three-part Lost Land of the Volcano, showing on BBC1. It has been greeted by gasps of “wow” at the gung-ho derring do.

In the first episode alone Steve Backshall, the naturalist, stalked crocodiles, drifted into a whirlpool, wrestled a snake and climbed into a cave mouth halfway up a cliff, said to be home to a giant serpent, then set about mapping the white-water river churning inside it.