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SILURAN PERIOD

444-416 million years ago

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fish

The ancestor of acanthodians and bony fish evolved a few modifications of the skull.

In acanthodians, the skull was composed of small bones rather than the large plates typical of the placoderms. In acanthodians, the hyoid apparatus was similar to that of primitive actinopterygians and sarcopterygians (Carroll). Acanthodians also possess a dentary bone in the lower jaw and the quadrate bone in the upper jaw (Kardong, 2002, p. 248; Carroll, p. 88). Acanthodians possessed homologs of the parasphenoid and basisphenoid (Carroll, p. 87).