The lion is a muscular, deep-chested cat with a short, rounded head, a reduced neck and round ears. The colour of its fur varies from light buff to silverly gray, to yellowish red and dark brown. The underparts are generally lighter, and cubs are born with dark spots on their bodies. The spots fade as lions reach adulthood, although faint spots often may still be seen on the legs and underparts. The lion is the only member of the cat family that displays obvious sexual dimorphism.
Males are more robust than females, have broader heads and a prominent mane, which grows downward and backward and covers most of the head, neck, shoulders, and chest. The mane is typically brownish and tinged with yellow, rust, and black hairs. The most distinctive characteristic shared by both females and males is that the tail ends in a dark, hairy tuft. In some lions, the tuft conceals a hard “spine” or “spur”, approximately 5 mm (0.20 in) long, formed of the final sections of tail bone fused together. The lion is the only cat with a tufted tail, but the function of the tuft and spine are unknown. Absent at birth, the tuft develops around 5 1⁄2 months of age and is readily identifiable at the age of seven months.
Of the living, non-hybrid felids, the lion is rivalled only by the tiger in length, weight and height at the shoulder. Its skull is very similar to that of the tiger, although the frontal region is usually more depressed and flattened, with a slightly shorter postorbital region and broader nasal openings than that of a tiger.
Due to the amount of skull variation in the two species, usually only the structure of the lower jaw can be used as a reliable indicator of species. The size and weight of adult lions varies across global range and habitats.