Dinosaurs have learned to walk using only their hind legs during their evolution. Scientists have found out why; it was because of the need for speed.

Paleontologists have created a new theory explaining the reason of dinosaurs just using two feet instead of their four legs. During the pre-historic times, there were smaller dinosaurs called proto-dinosaurs, Science Daily has reported. The evolution started with them. These small dinosaurs learned how to walk using only their two hind legs to run faster.

They succeeded with the evolution because of their tails, said Scott Persons, postdoctoral fellow and lead author on the paper. The tails of the proto-dinosaurs are very strong and it empowered the hind legs, Persons added. "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 has explained.

The known theory about it happening for the dinosaurs to catch their prey is wrong. The reptiles would fall down, face flat to the ground if they will catch their prey using their front legs. They would fall down as it will be harder to balance when they have more weight on their front legs, the research conducted by Persons and Phil Currie, paleontologist and Canada Research Chair, stated. Moreover, there were many herbivorous dinosaurs that evolved into two legs and they do not even catch prey. In addition, many carnivorous dinosaurs have small front legs that look like their tiny hands so they are not able to catch their prey using it, National Post said.

Many lizards are back on all four legs this period. It might be because they have lost the power of their tails, Persons said. Also, mammals like horses, which run fast, are also running on all fours. Meanwhile, kangaroos run/jump on two legs because they have strong tails.