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Early tetrapod all had sprawling gaits and faced a significant problem in terrestrial locomotion. Their respiration and movement used much the same sets of muscles, and both systems could not operate efficiently at the same time. It is known as, Carrier’s Constraint.
Very early dinosaurs already had developed an entirely upright stance. Therefore, their interaction with other organisms such as human beings and birds in their community might have led to emergent properties. For instance, humans, through interaction with the dinosaurs developed a bipedal posture over time thus also relieving Carrier’s Constraint. That is because, in a biped, the thorax is lifted off the ground, the forelimbs are no longer involved in support and locomotion, and the rib cage does not flex laterally during motion.
Another example is the bird’s crouching gait. Whereby, a bird’s legs are bent into a zigzag, putting them in a crouched position. Therefore, it is assumed that birds evolved from the earliest of bipedal dinosaurs because their gait shows an evolutionary adaptation born of their dinosaur ancestors.
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