500 million years ago, the world was a very different place. During this period of time, known as the Cambrian period, basically all life was in the water. The ocean was brimming with animals that looked pretty different from the ones we recognize today — including a group of predatory worms with a throat covered in teeth and spines.

Researchers thought these tiny terrors died out at the end of the Cambrian period. But a paper published recently in the journal Biology Letters showed examples of a new species of this worm in the fossil record 25 million years after scientists thought they'd vanished from the Earth. One of the authors of the paper, Karma Nanglu, tells us how this finding may change how scientists understand the boundaries of time.

Curious about other weird wonders of the ancient Earth? Email us at shortwave@npr.org.