Roundworm life cycle. A roundworm is a type of nematode (ascarid) that reproduces in the intestinal tract of its host. Dogs are the host for Toxocara canis, and cats are the host for Toxocara cati.

Though the ancient worms in the study died, that outcome was not unexpected given their life cycle, Dr. Kurzchalia said. “Sleeping Beauty, when she came out, she didn’t live another 300 years ...