On April 25, 1977, the Japanese trawler Zuiyo Maru was working off the coast of New Zealand when its nets caught a foul-smelling, decomposing corpse that measured about 10 meters long and weighed two tons.

To avoid spoiling the fish catch, the captain decided to dump the carcass back into the ocean, but the crew first took some photos and measurements. The creature had a neck 1.5 meters long, four large, reddish fins, and a tail about 2 meters long, and it lacked a dorsal fin.

The story made a sensation in Japan, and the shipping company belatedly ordered all its boats back to relocate the dumped corpse, without success.

Some scientists declared the creature to be a prehistoric plesiosaur; others thought it might have been an oversized basking shark. Fujiro Yasuda of Tokyo University said, “We can’t find any known species of fish that correspond with the animal caught outside New Zealand. If it is a shark, it is a species unknown to science.” We’ll never know.