Answer
The original tetrapod gait would have inhibited processes requiring oxygen during movement, especially the use of the brain, as well as having limited the amount and speed of movement possible since oxygen would be needed to maintain activity. The evolution of a gait which did not compress the lungs and inhibit breathing would have allowed for more sustained activity as well as more complex activity since the brain, which demands lots of ATP made using oxygen to break down food, could work at a high level while vigorous movement was occurring.
Work Step by Step
Use your imagination to identify what a lack of oxygen would limit with the original gait described (reviewing aerobic cellular respiration in early parts of the book will also help), and what would be possible once that limited gait was lost.
