"This gives us a maximum timeframe of 35 years for this rock formation, well within the course of a single human lifetime.

As night fell across a swamp in southern Vietnam, a “large” fanged creature sat in the murky water. Its reddish eyes scanned the surrounding forest, but it wasn’t the only one looking.

The crew at the aquarium were familiar with the fish, which had fanged teeth within a wide mouth and measured nearly 5 feet long, as a longnose lancetfish. Known to swim as deep as over a mile ...