Complex sentence: The first having a Dalcassian origin, located in Corco Modhruadh County Clare, were a distinguished learned family, and hereditary historians to the O’Briens of Thomond.
Split into simpler sentences: The first having a Dalcassian origin, and located in Corco Modhruadh, were a distinguished learned family. They were hereditary historians to the O’Briens of Thomond.