heterostraci
/ˌhɛtəroʊˈstreɪsaɪ/
noun
- An order of extinct jawless fish with a bony head shield, often used as a plural term for the group.
- Unlike later fish, Heterostraci had no paired fins.
- The classification of Heterostraci helps paleontologists map early fish evolution.
- Heterostraci lived in ancient seas and left behind many fossils.