About 500 million years ago, the Grand Canyon was a great sea, and among the creatures it harbored was a newly discovered type of penis worm, armed with many rings of teeth. Penis worms are marine creatures with a distinctly phallic appearance. Lining this throat were rings and rings of teeth. This is much larger than the species of penis worm that survive today, which have undergone miniaturization over the millennia and now do not exceed 2 to 3 millimeters. Although the phallic worm monopolized scientists’ attention with its teeth, fossils of other creatures were also found in the same expedition.