let us start with saying that evolution is creatures' development during many generations, therefore we should mention that the more we dig into the ground and reach levels that are more ancient, we should find creatures that belong to the more previous eras. i.e., in the closest ground level we will find the last creatures, once we dig more, we will find their ancestors; if we dig more, we will find their ancestors, because each were developed from those before and their remains were left inside the ground's geological levels.