Palaeontologists have come up with a theory to explain why the ancient ancestors of dinosaurs quit walking on all four legs and became bipedal, that is using two legs to walk.
Dinosaurs inherited bipedal from the ancestors called proto-dinosaurs. Proto-dinosaurs were much smaller in size. According to palaeontologists, proto-dinosaurs could walk on their two hind legs because of their tails that were big and had leg-powering muscles. These muscles provided strength required to be able to stand on and walk around on their hinds.
Later, evolution like elongation of hind limbs enabled these proto-dinosaurs to run faster and for longer distances. Also, smaller forelimbs helped them to balance their weight on their hinds.
This theory punctures theories that suggested dinosaurs evolved to become bipedal to be able to catch preys with their free forelimbs. This theory states that dinosaurs used their powerful jaws and not forelimbs to catch preys.
But the question arises, why aren’t mammals like tigers, lions and horses bipedal?
Palaeontologists explain that mammals don’t have strong tails with leg-powering muscles. Ancient mammals lost these tail muscles because they were adapting to dig and to live in burrows. To dig, they needed stronger forelimbs. Muscular tails would have hampered manoeuvring. Living in burrows helped the ancient mammals to survive a mass extinction. It also enabled some of them to become fast runners.