Welcome to PokéCommunity! Register now and join one of the best fan communities on the 'net to talk Pokémon and more! We are not affiliated with The Pokémon Company or Nintendo.
I think the idea is that when Pokemon were first being created Cubone was going to be the pre-evolved form of Kangaskhan. Then the idea got tossed out and instead Cubone was given the evolution Marowak and Kangaskan was left as a non evolved Pokemon.
That's just a theory that's thrown around a lot though. I don't think there is any facts based to it.
I, personally, don't think this thread has a point. Firstly, it's in the wrong forum. Secondly, we've noted the similarities and differences about Cubone and Kangaskan. Thirdly, your point isn't that observant because we can see from every angle that Cubone has a small face.