Having a comparatively or relatively small head; microcephalic or microcephalous.
The Century Dictionary (Public Domain)
Use "small-headed" in a sentence
"Take my small-headed conceptions about the beginnings of ecotourism."
"His admittedly long-legged and small-headed temptresses (funnily enough, he often used his own daughter as his model) adorned calendars, magazine centerfolds and covers, and were often painted as "nose art" on war planes during World War II."
"The Frog Method holds true for quite a few small-headed animals, apparently."