Complex sentence: The endemic fauna bridges a massive gap in the history of South America's endemic mammals; paleontologists knew the earlier sloth and anteater forebears of 40 mya, but no fossils from this transitional age had been seen.
Split into simpler sentences: The endemic fauna bridges a massive gap in the history of South America's endemic mammals. Paleontologists knew the earlier sloth and anteater forebears of 40 mya, but no fossils from this transitional age had been seen.