THE LAST TIME our paleontological feelings took off in a happy soar was two years ago when some diggers in the Big Bend National Park in Texas unearthed the remains of the Cretaceous pterosaur. That was the flying reptile with 51 feet of wingspan that goes back a timespan of over 60 million years when it last ruled the hemisphere's skies. While wondering if the pterosaur would be allowed to land at Dulles if it lived today, we were delighted - as were any others - by the uncovering of evidence that this mighty reptile had once been here.

Now a new moment of delight has come - and gone. A Japanese fishing crew, trawling in the waters off Christchurch, New Zealand, pulled up a two-ton carcass that paleontologists believe was a plesiosaurus. That immense reptile, which thrived 100 million years ago, apparently had such prehistoric body odors that the Japanese fisherman heaved it overboard, back into the silence of the deep.

The fishermen are now in deep trouble with the paleontologists for failing to bring back to the lab what one scientist called "possibly the find of the century." The sunk feeling among the paleontologists is understandable, but the fishermen, more concerned about reeling in the finds of the day, have a fair defense. They did take color photographs, in the best tradition of Japanese zeal for skilled camera work: by doing so they dutifully let the world know that they were wise enough to realize this wasn't another hunk of ocean litter. It was merely the stench, plus the fatty liquids oozing from the creature onto the deck - which presumably would have to have been swabbed down before arriving back in port - that prompted the crew to deep-six the supposed plesiosaurus.

One fact for sure: This creature didn't swim into the 20th century on its own. Unless the line has suddenly run out, after being thought lost for 100 million years, other plesiosauri also are in the waters off New Zealand. We can't imagine the paleontologists' resisting their timeless urges to root among the mysteries of the past. With the help of a bathysphere or two, and with thanks to the Japanese fishermen, their search is likely to come up with something more substantial than whatever it is - or isn't - that continues to frustrate the monster-watchers at Loch Ness.