Complex sentence: Original drummer Alexander "Skip" Spence had left the band in mid- 1966, replaced by Los Angeles jazz drummer Spencer Dryden, a half-nephew of filmmaker Charlie Chaplin.
Split into simpler sentences: Original drummer Alexander "Skip" Spence had left the band in mid- 1966. He was soon replaced by Dryden, an experienced Los Angeles jazz drummer and the half-nephew of filmmaker Charlie Chaplin.