Here is a useful site . Here
I use it for my detective work when I want to track somebody and his identity.
It is really amazing, I have been using it for a some time now. You can go all the way back to Newton and Barrow!
It is interesting to say, that most mathemations did have Ph.D's but not all. If you try you can manange to find some. For example, Karl Weierstrass, he is contained within the site but his Ph.D. thesis is not mentioned because he never got one. Another example, is Ludwing Sylow.
According to that site, Gauss, was only 21 (or maybe 22) when he got his Ph.D. in mathematics.
That means you can find out to who you are mathematically related to.