Evolution has produced a steady stream of now-extinct terrifying creatures, but if they were around today, some could destroy the Earth as we know it.

De-extinction — the science of resurrecting extinct species — is progressing in leaps and bounds. Here are six creatures that researchers could bring back to life.

Reintroduction of captive-bred animals has had mixed success. This California butterfly lost habitat to grazing and drought and is considered to be extinct. The last live one was seen in the wild ...