Now, this is one weird-looking animal. It's called Thylacosmilus, and it was a South American marsupial that lived around three million years ago. Note the huge saber teeth, as big as those of the saber-toothed cat, or Smilodon, that lived quite a bit after Thylacosmilus. But even weirder is the lower jaw that accommodated those teeth. A comparison between Thylacosmilus and Smilodon reveals that despite the teeth, they were very different animals.
At a time when South America was still an island, Thylacosmilus did not occupy Smilodon’s apex niche. Large “terror birds,” which could grow taller than a person, with a two-foot long skull that was mostly beak, may have been the dominant carnivores. Thylacosmilus appears to have filled a unique ecological niche, one that even modern scavengers, such as the relatively indiscriminate, bone-chomping hyena, don’t quite fit: a scavenger that was careful with its food, targeting the softest tissues, such as internal organs rather than muscle or bone.