Descended from the baboons that flourished on the grasslands during the age of human rule, their diet changed from omnivorous to carnivorous during the period that the big cats of the grasslands died out. At the same time they increased their speed by taking to their hind limbs and adopting a totally bipedal locomotion. The fore-limbs became reduced and the head was carried further forward, balanced by a thick, heavy tail. In physical form the raboon bears a distinct resemblance to the carnivorous, non-avian theropod dinosaurs that died out at the end of the Mesozoic.