The phrase "rounded skull" means that someone has a head shape that is smooth and curved rather than having sharp or pronounced angles.
Sentences with «rounded skull»
These puppies do feature rounded skull with a wide dome. (barkrescue.net)
They have large heads with rounded skulls, dark eyes, boxy muzzles and thin ears that hang somewhat close to the head. (dogster.com)
On the very last morning, his team discovered a yellow piece of rounded skull cap protruding from the muddy floor of the pit, in the same layer where he had found the tools. (sciencemag.org)