A group of prehistoric armored fish with shield-like head plates, representing an extinct class of early vertebrates.
From Greek 'aspis' (shield) + 'kephalē' (head), literally 'shield-headed,' describing the distinctive bony armor covering their heads.
These fish were covered in bony plates like walking tanks—when they dominated Earth's oceans 400 million years ago, they were the ultimate predators before sharks even evolved!
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