Complex sentence: The Baja California Peninsula appears on some early maps as an island but was later discovered to be attached to the mainland of North America; likewise Banks Peninsula off the South Island of New Zealand which was originally called "Banks Island" by Captain James Cook.
Split into simpler sentences: The Baja California Peninsula appears on some early maps as an island but was later discovered to be attached to the mainland of North America. Similarly, the Banks Peninsula off the South Island of New Zealand which was originally called "Banks Island" by Captain James Cook.