London, Scientists have discovered new species of fanged frog, grunting fish and a giant rat, probably the biggest in the world, in a remote volcanic crater in Papua New Guinea islands.

A team of researchers from Britain, the United States and Papua New Guinea have found more than 40 previously unidentified species in the kilometre-deep crater of Mount Bosavi, lying untouched since 200,000 years, the Guardian newspaper reported.

The biologists discovered in the the three-kilometre wide crater 16 frogs which have never before been recorded by science, at least three new fish, a new bat and a giant rat, which may turn out to be the biggest in the world. Other predators included giant monitor lizards and kangaroos which have evolved to live in trees.

"It was mind-blowing to be there and it is clearly time we pulled our finger out and decided these habitats are worth us saving," said Dr George McGavin who headed the expedition.

New species discovered include a camouflaged gecko, a fanged frog and a fish called the Henamo grunter, named because it makes grunting noises from its swim bladder.

"These discoveries are really significant," said Steve Backshall, a climber and naturalist.