heads and a prominent mane that grows downwards and backwards covering most of the head, neck, shoulders, and chest. The mane is typically brownish and tinged with yellow, rust and black hairs. The tail of all lions ends in a dark, hairy tuft that in some lions conceals an approximately -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 months of age. It is readily identifiable by the age of seven months. Of the living felid species, the lion is rivaled 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, and has a slightly shorter postorbital region and broader nasal openings than those of the 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. Skeletal muscles of the lion make up 58.8% of its body weight and represents the highest percentage of muscles among mammals. Size The size and weight of adult lions varies across global range and habitats. Accounts of a few individuals that were larger than average exist from Africa and India. Mane The male lion's mane is the most recognisable feature of the species. It may have evolved around 320,000–190,000 years ago. 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 presence, absence, colour and size of the mane are associated with genetic precondition, sexual maturity, climate and testosterone production; the rule of thumb is that a darker, fuller mane indicates a healthier animal. In Serengeti National Park, female lions favour males with dense, dark manes as mates. Cool ambient temperature in European and North American zoos may result in a heavier mane. Asiatic lions usually have sparser manes than average African lions. Almost all male lions in Pendjari National Park are either maneless or