Anthracosaurs consolidated their occipital region
and the stapes was reduced in size. Amniotes use the stapes as a middle
ear bone which facilitates hearing.
In anthracosaurs, the postparietal bone was reduced and the tabular contacted
the parietal. The stapes is reduced. Seymouria was not ancestral to reptiles
(because of its late date) but its ancestors reduced the size of the stapes
even further (Clack, 2002).