>It was the size of a polar bear, with a mouth full of slash-ing blades. Some 22 million years ago, in what's now Kenya, the mega-carnivore Simbakubwa kutokaafrika ruled. Then it disappeared. The last of Simbakubwa's lineage, carnivores known as hyaenodonts, went extinct more than 10 million years ago. Mostly fragmentary fossils of dozens of species have been found around the world, some smaller than house cats. Other species were much larger, but researchers had few clues about when these giants evolved.
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