A lot of the time in anime the character’s skull shape is implied by hair growth. Obviously, it’s not a hard and fast rule, because most artists work by pure instinct, and some are subversive on purpose. But it’s interesting that these tropes probably didn’t occur by accident, but rather because we expect these shapes to accompany certain personalities.
Shonen hair grows large in all directions. This implies bigskull, which I’ve recently theorized is a personality force multiplier. Bigskull is almost always associated with “big” names: Political Potential, Matt Forney, Illuminatus, etc.
Slipknot ponytail implies melon top. Probably this was also its purpose in real life, and you see similar hairstyles to indicate high class today and throughout history (especially among women).
Vegeta’s slightly backswept, straight-up spiky hair implies bigmelon.
I don’t know what this one is called, but I see it everywhere and it almost definitely implies large occipital.
Bangs generally imply deep sockets. Again, this is probably also the general intent in real life.
That should get you started.