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With a lethal combination of bone-crunching bite forces, stereoscopic vision, rapid growth rates, and colossal size, tyrant dinosaurs reigned uncontested for 15 million years leading up to the end-Cretaceous extinction -- but it wasn't always that way, when and how quickly tyrannosaurs went from wallflower to prom king has been vexing paleontologists for a long time. The only way to attack this problem was to get out there and find more data on these rare animals.