Was it a hoax? A deep-sea version of the Loch Ness monster? Or a prehistoric plesiosaurus?

Excited natural history experts believe that the mysterious two-ton corpse caught off New Zealand may have been the latter - a huge reptile thought to have died out 100 million years ago. No one can say for sure, though because whatever it was smelled like the dickens, prompting the Japanese fishermento dump what one paleontologist described as "possibly the find of the century" back into the briny.

The 2,460-ton Zuiyo Maru was trawling off Christchurch, New Zealand, last April 10 when its net snared the unidentified dead animal at 1,000 feet. Hoisted to the surface the creature was about 32 feet in length, with four flippers and a long neck and tail.

The overpowering stench and the unpleasant fatty liquids oozing onto the deck overcame the fishermen's curiosity over an animal neither they nor any of or study. On the bais of color photographs and sketches the natural scientists since consulted had ever seen before. Afraid that the animal would spoil their cargo fish they took measurements and photographs and dropped the corpse back in the ocean.

Japanese paleontogists are aghast that the animal's skeleton was not preserved for study. On the basis of color photography and sketches made by Michihiko Yano, 39, a fishery company executive who was on the trawler, they believe it may have been a plesiosaur is known to have lived in the seas off eastern Australia.

"It's not a fish, whale or any other mammal," said Prof. Yoshinori Imaizumi, director general of animal research at the National Science Museum. "It's a reptile and the sketch looks very like a plesiosaurus."

When Yano returned to Japan last month, his photos and sketch and notes were passed over to Imaizumi and other professors for study.

After the Asahi Shimbun broke the story today, Imaizumi said: "This was a precious and important discovery for human beings. It seems to show that these animals are not extinct after all. It's impossible for only one to have survived. There must be a group."

If verified, the existence of living plesiosaurs would be an astounding discovery. The available evidence does not allow a definite conclusion, yet natural historians certainly do not dismiss the possibility that descendants of the prehistoric giants may be lurking in the great depths of the southern seas. The marine environment is generally more favourable than land for the survival of dying species, they say, and if plesiosaurs exist anywhere the southern seas are a good bet.