The lion is a muscular, deep-chested cat with a short, rounded head, a reduced neck and round ears. Its fur varies in colour from light buff to silvery grey, yellowish red and dark brown. The colours of the underparts are generally lighter. A new-born lion has dark spots, which fade as the cub reaches adulthood, although faint spots often may still be seen on the legs and underparts.
The lion's mane is the most recognisable feature of the species. It starts growing when lions are about a year old. Mane colour varies and darkens with age; research shows its colour and size are influenced by environmental factors such as average ambient temperature. Mane length apparently signals fighting success in male–male relationships; darker-maned individuals may have longer reproductive lives and higher offspring survival, although they suffer in the hottest months of the year.
The tail of all lions ends in a dark, hairy tuft that in some lions conceals an approximately 5 mm long, hard "spine" or "spur" that is formed from the final, fused sections of tail bone. The functions of the spur are unknown. The tuft is absent at birth and develops at around 5 1⁄2 months of age. It is readily identifiable by the age of seven months.
