420 million years ago, some fish were more medieval. They wore armor, sometimes made of big plates, and sometimes made of interlocking scales. But that armor may actually have served a totally different purpose, one that many animals still use today.

Originally released by Knowledgemotion, 2018. Streaming video file encoded with permission for digital streaming by Infobase on February 21, 2020.

When Fish Wore Armor (10:19); .