Complex sentence: Rainbow skinks are the only introduced reptile that has successfully established itself outside of captivity in New Zealand where they have been present since an accidental introduction from Australia in the early 1960s, and are currently well established in several regions of the North Island.
Split into simpler sentences: Rainbow skinks are the only introduced reptile that has successfully established itself outside of captivity in New Zealand. They have been present in this country since an accidental introduction from Australia in the early 1960s, and are currently well established in several regions of the North Island.