Some contemporary vinyl toys have bulbous heads. Matangos, RxH Chaos, and some of the Blobpus sculpts come to mind.

Are there instances of this in vintage?

I am guessing that this is a sign or indication of radiation. Yes? Np?
At least in the movies.

for certain vintage advert. toys all are top heavy head wise.. lil green sprout, pillsbury dough boy, nabisco spaceman, florida orange bird, cap'n crunch, etc..

one of my favorites is Quisp so happy its made again!

are you familiar with Tomland star raiders? they are knockoff quality blow molded with vinyl heads, the scuplts are outta this world and most feature bulbous heads. they all have a kaiju feel about them aesthetically.

radiation fx do seem to be the cause for most haha. my thought is they made the heads so big because that was always the focal point in the ads.

best bulbous head ever= billikens "invasion of the saucermen" creature! when that came out I was in high school and it took me 2 months to save up the $33 it cost back then.

I am scared.
I admit that I ate this vitamin powered sugary cereal.
I was thinking more toward toys with bumps on their heads.