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Evolution of Early Fish: Exploring Ostracoderms and the Rise of Jawed Fishes

The Ordovician Period (425-500 million years ago) marked the presence of ostracoderms, slow, bottom-dwelling animals covered in thick bony plates and scales. Lacking well-developed fins and jaws, they are believed to be among the first vertebrates to roam the oceans. By 395 million years ago, two groups of fishes with movable jaws emerged, characterized by their distinct anatomy. The evolution of chondrichthyans approximately 410 million years ago and bony fish (osteichthyans) laid the groundwork for modern aquatic ecosystems.

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Evolution of Early Fish: Exploring Ostracoderms and the Rise of Jawed Fishes

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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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