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SILURAN PERIOD

444-416 million years ago

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FISH

The ancestors of cartilaginous fish and higher vertebrates evolved a hyoid arch and teeth with both enamel and dentin.


In early fish, and in sharks and some primitive bony fish alive today, the vertebrae are more extensive although they have not replaced the notochord. They simply develop around the notochord which still runs uninterrupted from head to tail, Cartilaginous fish develop a hyoid arch and possessed teeth with both enamel and dentin (Carroll, p. 66).