Birds fly using their entire forelimb, but the large bones are filled with air spaces, making them very lightweight, and many of these hollow bones are fused together for extra strength. The bat flies with its finger bones, which are more solid than bird bones, but just as lightweight because they are extremely slender. Examine the skeletons on display . Notice the different ways that the limbs are held in relation to the body, and compare them to the diagram below. In primitive amphibians, the legs are held out towards the side and flat on the ground, much like the fins of the fishes they evolved from.
Reptiles have a semi-improved posture .
Their legs are held away from the body at an angle, and they can push their bellies off the ground as they run. Dinosaurs, birds, and mammals have a fully improved posture . Their legs are held completely under their bodies. Consider This Conscious awareness is the ultimate product of evolution. Born from stardust, we are truly the universe becoming aware of itself.