The common ancestor of Casineria and amniotes had modified its vertebrae
so that the pleurocentra were increasingly dominant over intercentra,
the ribs were long and thin, the arm bones slender. The number of digits
on the hands and feet was limited to five and the curved last phalanx
improved its grasp.Like most early amphibians, the skull contained many
bones which modern amphibians lack but which are components of the skulls
of rhipidistian fish.