Perhaps the most remarkable Neotropical dinosaurs are the pachamacs, gigantic ornithopod dinosaurs that look like mirror-images of the true, saurischian sauropods that were once abundant throughout South America. The origin of the pachamacs is obscure, but genetic studies suggest their closest relatives are the neodryosaurs of Australasia and Madagascar, although they appear to have even split from these sometime in the early Cretaceous. Their most likely origins lie with small, poorly-known South American late Cretaceous ornithopods such as Talenkauen santacrucensis.