One of the keys to the dinosaurs' success was their way of walking upright on straight legs. This gave them an advantage over other animals groups, which were sprawling walkers, and later allowed them to adopt a wide range of lifestyle. Plodding giants, huge hunters, roaming herds and single-footed scavengers each evolved their own variation of walking upright.
Dinosaurs walked with straight legs tucked underneath their bodies. It was this ability, never achieved by any other reptile before or since, that opened the way to the evolution of a variety of body types and lifestyles. This helped them to become dominant land animals and remain so for 160 million years.
Four-legged land animals with a backbone (vertical column) walk in one of three ways. A lizard sprawls with legs held at right angles to its body. Forward movement is achieved by throwing its weight from side to side and moving its legs one at a time. A crocodile also sprawls most of the time but can sprint for shorter distances with its legs nearly straight and its body lifted off the ground. This is called the "improved stance". All mammals and birds have a fully improved stance with legs held straight under the body at all times, whether walking, running, galloping or hopping. Humans walk like this and so did dinosaurs.
Having a fully improved stance allows an animal to grow bigger, walk further and more faster, and this opens the evolutionary path to a huge range of body types and lifestyles. This can be clearly seen with todays' fully improved walkers, birds and mammals - some are huge, some fast, some tall, some agile. The dinosaurs too, having once achieved fully improved walking, evolved to exploit it in many different ways.
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