Complex sentence: Xenarthrans developed and diversified extensively in South America during its long period of isolation, invaded the Antilles by the early Miocene, and then spread to Central and North America starting about nine million years ago, as part of the Great American Interchange.
Split into simpler sentences: Xenarthrans developed and diversified extensively in South America during its long period of isolation. They invaded the Antilles by the early Miocene and, starting about nine million years ago, they spread to Central and North America as part of the Great American Interchange.