Ornithomimosauria

Ornithomimids
When it comes to evolution, there will always be winners and loosers. But things aren't always this clear cut, and sometimes a group that looks like it's on its way out gets a new lease on life. Such is the case with the ornithomimosaurs, a group of coelusaurian theropods which developed a herbivorous lifestye. Best known for Late Cretaceous species such as Gallimimus , the group went into a gradual decline due to newer forms of herbivorous dinosaurs, most notably the cursiohadrids. Although able to process and digest grass the cursiohadrids were better at it, as were the rapidly diversifying fowl who had the added benefit of flight. By the late Miocene ornithomimids were reduced to a single genus found in high altitude mountain ranges. The ice ages changed all that. The simple fillaments that covered ornithscian bodies made them struggle against the cold but ornithomimids and their coats of proper feathers did not have this issue. Thus they were able to descend from the mountains, and today are common in the northern hemisphere around the Arctic Circle. They are also still common in the mountains, and due to the great distances between mountain ranges they are at their most speciose at high elevations. Over time the one genus has split into three, and there are roughly 15 living ornithomimid species.