Complex sentence: The ancestors of thylacoleonids are believed to have been herbivores, which is unusual for carnivores but cranial features and arboreal characteristics suggest that thylacoleonids share a common ancestor with wombats.
Split into simpler sentences: The ancestors of thylacoleonids are believed to have been herbivores, something unusual for carnivores. Cranial features and arboreal characteristics suggest that thylacoleonids share a common ancestor with wombats.