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HISTORY

HISTORY. Ordovarian Period (425-500 million years ago) OSTRACODERMS Slow, bottom-dwelling animals Covered with thick bony plates and scales Had very poorly developed fins and didn’t have jaws Believed to be the first animal with backbone Extinct about 250 million years ago.

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HISTORY

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  1. HISTORY • Ordovarian Period (425-500 million years ago) • OSTRACODERMS • Slow, bottom-dwelling animals • Covered with thick bony plates and scales • Had very poorly developed fins and didn’t have jaws • Believed to be the first animal with backbone • Extinct about 250 million years ago

  2. 2 Groups of Fishes with movable jaws • Appeared about 395 million years ago • Had thick, bony plates and paired fins • Their upper jaw was fused to the skull while the lower jaw was hinged and movable • Extinct about 345 million years ago • Class Chondrichthyesevolved • Appeared about 410 million years ago • Distinguished by the bony spines projecting in front their fins and by minute diamond-shaped scales • Class Osteichthyes evolved PLACODERMS ACANTHODIANS

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