E.g. Sphenodon is a relict of a primitive diapsid radiation, appearing quite different from alligators and birds, which are derived, not primitive, diapsids. MA's descendants differ from what MA looked like in curious ways. A whole Linnean Class of Gnathostomes now extinct, the wondrous looking Placoderms. Paleozoic sharks with antler-like dorsal spines that may have served for sexual selection. This lineage eventually branches into a amazing diversity of teleost fishes, about 20,000 species of them.
Most adaptations are complex, making understanding the process of adaptation difficult.
Suppose that such complex evolutionary changes that make up these kinetic skulls arise incrementally, and not in one fell swoop. Each small increment of change can often be seen as being adaptive and hence under selection.