However, the sinuous motion of the body alternately collapses the lung on each side, preventing breathing during running. That's why lizards have to stop completely and pant after they run, even though they risk capture. A sprawling posture and gait was probably typical for most non-Archosaur Archosauriformes. When moving slowly, their posture is sprawling, but when they run, their body straightens out and they pull their legs nearly under their body. In this posture the lungs can still operate.
Some crocodiles are even capable of galloping.
Galloping is the fastest type of longer term quadrupedal motion in which all four feet are off the ground simultaneously during one phase of the step cycle. The limbs move in this parasagittal plane during walking slowly as well as running. This allows easy breathing while running. The open acetabulum is the culmination of the permanent attainment of the erect posture. The open acetabulum is associated with a series of logical mechanical features related to the erect posture and gait of dinosaurs.