Why does a staffies head split?

Breeds such as Staffordshire Bull Terriers and American Staffordshire Terriers have a signature ''head split'' as they become adults at about six months to a year. This distinct formation of the skull means that the bone is fused strongly together, giving these breeds very hard heads! This serves no real purpose other than for more protection for the brain and is nothing to worry about as the vast majority of purebred Staffies have it. It does not hurt the dog and can be compared to the fusing of a child's skull as it grows older.