Toronto, March 4 (IANS) Big muscles in the tails of early dinosaurs helped them move about on all fours and rise up on just their two back feet, new research suggests.Bipedalism in dinosaurs was inherited from ancient and much smaller proto-dinosaurs. The trick to this evolution is in their tails, said lead study author Scott Persons, postdoctoral fellow at University of Alberta in Canada. "The tails of proto-dinosaurs had big, leg-powering muscles," Persons said. "Having this muscle mass provided the strength and power required for early dinosaurs to stand on and move with their two back feet. We see a similar effect in many modern lizards that rise up and run bipedally," Persons added.Over time, proto-dinosaurs evolved to run faster and for longer distances. Adaptations like hind limb elongation allowed ancient dinosaurs to run faster, while smaller forelimbs helped to reduce body weight and improve balance, according to the study published in the Journal of Theoretical Biology.Eventually, some proto-dinosaurs gave up quadrupedal walking altogether.The research also debunks theories that early proto-dinosaurs stood on two legs for the sole purpose of freeing their hands for use in catching prey."Those explanations don't stand up," Persons said. "Many ancient bipedal dinosaurs were herbivores, and even early carnivorous dinosaurs evolved small forearms. Rather than using their hands to grapple with prey, it is more likely they seized their meals with their powerful jaws," Persons explained.But, if it is true that bipedalism can evolve to help animals run fast, why aren't mammals like horses and cheetahs bipedal?"Largely because mammals don't have those big tail-based leg muscles," Persons said.