The speed of a racing grayhound is simply offscale to the speed of a teacup Chihuahua...
The scale isn't important, it is the structure and mechanism by which they are supported. A chihuahua is the same species as a grayhound: they both have idential locomotive biology. They just differ in scale, and so their resulting movement differs in scale. We are apes: we have the same neural biology as other apes. We differ from an Orang, for example, in scale of different neural features, and so we differ in mental capacity as a result. I share almost all of my DNA with at least one of my parents. They are probably about as smart as I am. I had considerably more education than either of them, so my academic achievement differs as a result.