An extinct class of early jawless fish from the Paleozoic era, characterized by bony armor plating of varied composition.
From 'hetero-' (different) + 'straca' (Greek 'ostrakon,' shell/armor). Named for their varied bony armor plates, unlike the uniform plates of some other armored fish.
Heterostracan fish were armored tanks from 500 million years ago—they mixed and matched different types of bony plates like nature was experimenting with armor design!
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