heterostracan
/ˌhɛtəroʊˈstrækən/
noun
- An extinct group of jawless fish from the Paleozoic era, having a bony head shield.
- Scientists study heterostracans to understand early vertebrate evolution.
- The museum displayed a fossilized heterostracan from the Silurian period.
- Unlike modern fish, a heterostracan had no jaws and a heavy armored head.