A whale that beached itself in Japan this summer has turned out to be one of the best examples ever seen of an extremely rare species, scientists have said.

The creature, which died soon after coming ashore in July, has been identified as a Longman's beaked whale.

We buried it without knowing exactly what it was Nobutaka Kubo, marine researcher

"It was amazing that we found such a rare whale," Nobutaka Kubo, a marine researcher at Kagoshima City Aquarium, told the Associated Press news agency.

Japanese scientists realised soon after the animal was buried that it was unlike other whales known in Japanese waters and dug it up on 3 August to perform tests.

First complete example

They announced on Wednesday that the 6.5-metre (21-foot) female was one of the best adult specimens ever found.

"We did some follow-up on the whale because we buried it without knowing exactly what it was," Dr Kubo said.

Scientists examined the whale's skeleton, stomach contents and DNA.

They ruled out the possibility that it was one of seven related species based on the shape of its body, head and teeth, concluding that it must be a Longman's.

The species - Indopacetus pacificus - is known from just a handful of complete specimens and fragmentary remains found in South Africa, the Maldives and Kenya.

In 1926, HA Longman described the original find as a new species.

South African specimen

The Japanese report mentions whale remains found beached in South Africa in the summer of 2002, which they argue may not have been Longman's (although DNA studies waiting to be published suggest they were).

We know absolutely nothing about them Vic Cockcroft, whale expert

When the specimens were found in August, whale expert Vic Cockcroft said the discoveries were extremely important.

"It's amazingly valuable, simply because we know absolutely nothing about the animals because they have only been seen two or three times alive," he said.

"We don't know the maximum size, we don't know where they feed or what they feed on. I mean we know absolutely nothing about them, where they occur even," Dr Cockcroft said.

Diet of squid

As its name implies, it has a long, beak-like mouth, and is believed to normally inhabit waters far from shore.

From the shape of their teeth, scientists believe the whales feed on squid.

Experts do not know if they are endangered or merely seen rarely because they live far from humans in the Indian and Pacific Oceans.

The skeleton of the Japanese specimen will be displayed at the Kagoshima City Aquarium.