There are lots of possible explanations for why humans became bipedal, including changing ecosystems and food resources. But what if it was just so it was easier for early humans to beat the crap out of each other?
Modeled after the Troodon dinosaur, Troody is the brainchild of Peter Dilworth, MIT student. Six years in development, Troody can walk, sit and run. (This video mostly shows walking.)