An Estemmenosuchus mirabilis stands before a lake 255 million years ago in what is today the Perm region of Russia near the Ural Mountains. An ungainly plant-eater, it was the largest animal of its day and is known for its distinctive horns. Maybe not the most handsome of beasts, Estemmenosuchus mirabilis was an early ancestor of today's mammals. In this image it stands among several varieties of fern while cycads known as Bjuvia simplex populate the far side of the lake.