Humans and pangolins are the only mammals to take a two-legged stride, Kangaroos can hop on both feet. Although birds were bipedal, they were a family of theropod dinosaurs, because all dinosaurs came from bipedal ancestors. The oldest known member of the dinosaur group is the Ashelilosaurus, which lived about 245 million years ago in the middle Triassic period and was 1 to 3 meters long and bipedal.
A new theory about how ancient ancestors of dinosaurs stopped moving about on all fours and towered on just their two hind legs has been developed by Palaeontologists at the University of Alberta. The theory suggests that early Dinosaurs stopped moving about on all fours and rose up on just their two hind legs, thanks to their large, muscular tails. Having this muscle mass provided the strength and power required for early dinosaurs to stand on and move with their two back feet. A similar effect can be seen in many modern lizards that rise up and run on their hind legs.
It is believed that the form of moving on two legs instead of four was handed down from Dinosaur’s ancestors. Starting with the early proto-Dinosaur (Dinosaur-like animal) species, they evolved to enable them to run faster and for greater distances.
The Triassic dinosaurs developed into two main groups: sauropods and ornithischians.
The sauropods have two branches: one is the theropod, a two-legged carnivorous dinosaur that includes tyrannosaurs and birds; The other is the sauropod suborder, the earliest of which, like the gargoyles, was bipedal and carnivorous, but switched to a vegetarian diet in the lush forests of the Triassic.
Ornithosaurs also has two branches, one ceratosaurus and one armored.
The pachycephalosaurs and ornithosis of the ceratopsids maintained a bipedal gait, at least for running. The early Cretaceous was a group of small, fully bipedal dinosaurs that could run fairly well. More evolved were the Protoceratops of the Early Cretaceous and the Filoceratosaurus of the late Cretaceous, which weighed close to 200 kilograms and were mostly quadrupedal-footed, although their hind legs were still much more developed than their forelegs.
Armored dinosaurs include two famous groups, Ankylosaurus and Stegosaurus, the early Jurassic Scutosaurus, which represent their common ancestor, the small, scaly, two-legged dinosaurs. Later, as their scales became more and more developed, one group continued to cover the entire back and strengthen the sides, becoming ankylosaurus. The other group exaggerated the ridge and developed into the lower order of stegosaurus. As a result, the body becomes very heavy and loses the ability to walk on two feet.
So in dinosaurs as a whole, bipedal gait was more agile and active, and only some dinosaurs that were large or heavily armored lost this trait.
It’s not just the choice of dinosaurs, it’s the choice of almost all land quadrupeds: when it comes to speed, stand up and take big strides, dinosaur is special in their ancestors in the Triassic is adapted to the active ecological niche, the limb vertical downward anatomical structure, and have a lot of muscle attachments in the tail, the sinewy tail to balance movement so that they can be a two-legged walking as the norm, and thus in Jurassic rapid rise, dominated the land.