Complex sentence: Immediately before this separation, South America and East Antarctica were not connected directly, but the many microplates of the Antarctic Peninsula remained near southern South America acting as "stepping stones" allowing continued biological interchange and stopped oceanic current circulation.
Split into simpler sentences: Immediately before this separation, South America and East Antarctica were not connected directly. However, the many microplates of the Antarctic Peninsula remained near southern South America, acting as "stepping stones" and allowing continued biological interchange and stopped oceanic current circulation.