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DEVONIAN PERIOD

416-359 million years ago

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panderichthys

The skull of Panderichthys was intermediate between those of earlier rhipidistian fish (like Eusthenopteron) and the early tetrapods.

The ancestor of Pandericthys and tetrapods developed large frontal bones and modified the position of the external nostril. The structure of the squamosal and maxillary bones were intermediate between Eusthenopteron and tetrapods. These fish lost the hinge between halves of skull as the the postparietal and parietal bones fused. This hinge was not useful on land because the skull too heavy in air. During the evolution of the early tetrapods, more of the mass of the head was moved caudally. The opercular bones were reduced, indicating that these fish were breathing less through their gills and more through their lungs. Sutures evolved between skull bones replacing the ancestral overlapping junctions (Clark, 2002).