Complex sentence: No antelope species are native to Australasia or Antarctica, nor do any extant species occur in the Americas, though at least one saiga species occurred in parts of North America during the Pleistocene.
Split into simpler sentences: No antelope species are native to Australasia or Antarctica. Nor do any extant species occur in the Americas, though at least one saiga species occurred in parts of North America during the Pleistocene.