Slightly smaller than their Californian relatives, Galápagos sea lions range from in length and weigh between , with the males averaging larger than females. Adult males also tend to have a thicker, more robust neck, chest, and shoulders in comparison to their slender abdomen. Females, by contrast, have a longer, more slender neck and thick torso. The male's sagittal crest enlarges when he reaches sexual maturity, forming a small, characteristic bump-like projection on his forehead. Adult females and juveniles lack this trait and have a nearly flat head and little or no forehead. Galápagos sea lions, compared to California sea lions, have a slightly smaller sagittal crest and a shorter muzzle.