The anterolateral portion (squama) arises from the mesenchyme at 8 weeks of embryogenesis while the petromastoid portion develops later from a cartilaginous center at 6 months of fetal development.
During embryonic development, the anterolateral portion (squama) arises from mesenchyme at 8 weeks gestation, whereas the petromastoid portion develops later from a cartilaginous structure at 6 months of fetal development.