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PALEOZOIC ERA

CARBONIFEROUS PERIOD

318-300 million years ago

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PELYCOSAUR

Over time, the lacrimal bone shortened and the back of the skull solidified.

After primitive pelycosaurs, the length of the lacrimal bone was reduced and it no longer reached the nostril. In advanced sphenacodont pelycosaurs and therapsids, the maxilla replaced the lacrimal at the nostril. In the back of the skull, the occipital region began to solidify and, as a result, the stapes was no longer required for support and it became increasingly modified for hearing. In advanced pelycosaurs, the supraoccipital became more attached to base of skull and the otic capsule.