Kingdom of Desmond
In the seventh century, they split into two main clans. Cenél Fíngin descended from Fíngen mac Áedo Duib (d. 618) and became the O'Sullivans and MacGillycuddys. The McGillycuddy are a sept of the O'Sullivan's. A descendant of Fíngen was Feidlimid mac Cremthanin (d. 847). Clann Faílbe descended from Faílbe Flann mac Áedo Duib (d. 639) and became the MacCarthy dynasty, rulers of the Kingdom of Desmond following their displacement by the Normans. The O'Callaghans belong to the same line as the MacCarthys, while the MacAuliffes are a sept of the MacCarthys.