This might be true, however, too often I think scientists are using THEIR imagination and wishful thinking by assuming that animals who share common characteristics or appearance are descended from or related to each other. I don't know that that is true at all. For example, the pictures you just posted - there is some similarity just a one might say there is similarity between a small cat and a small dog (there are more similarities than you might initially consider once you think about it), however do cats and dogs have a common ancestor because they have some characteristics in common? I don't know. And I don't know how you go about proving such a descent either. Where is the proof other than visual similarities? What would constitute "proof" for this evolution? Personally I think scientists are as desperate to prove their belief in evolution as religious folks might be to prove it isn't true.
> often I think scientists are using THEIR imagination and wishful thinking by assuming that animals who share common characteristics or appearance are descended from or related to each other.
Genetic analysis. Look into it.
> do cats and dogs have a common ancestor because they have some characteristics in common?
Yes.
> Where is the proof other than visual similarities?
There is rather more to paleontology than just looking at bones.