The addax is a spiral-horned antelope. Male addax stand from 105 to 115 cm (41 to 45 in) at the shoulder, with females at 95 to 110 cm (37 to 43 in). They are sexually dimorphic, as the females are smaller than males. The head and body length in both sexes is 120 to 130 cm (47 to 51 in), with a 25 to 35 cm (9.8 to 13.8 in) long tail. The weight of males varies from 100 to 125 kg (220 to 276 lb), and that of females from 60 to 90 kg (130 to 200 lb).
The coloring of the addax's coat varies with the season. In the winter, it is greyish-brown with white hindquarters and legs, and long, brown hair on the head, neck, and shoulders. In the summer, the coat turns almost completely white or sandy blonde. Their head is marked with brown or black patches that form an 'X' over their noses. They have scraggly beards and prominent red nostrils. Long, black hairs stick out between their curved and spiralling horns, ending in a short mane on the neck.
The horns, which are found on both males and females, have two to three twists and are typically 55 to 80 cm (22 to 31 in) in females and 70 to 85 cm (28 to 33 in) in males, although the maximum recorded length is 109.2 cm (43.0 in). The lower and mid portions of the horns are marked with a series of 30 to 35 ring-shaped ridges. The tail is short and slender, ending in a puff of black hair. The hooves are broad with flat soles and strong dewclaws to help them walk on soft sand. All four feet possess scent glands. The life span of the addax is up to 19 years in the wild, which can be extended to 25 years under captivity.
The addax closely resembles the scimitar oryx, but can be distinguished by its horns and facial markings. While the addax is spiral-horned, the scimitar oryx has straight, 127 cm (50 in) long horns. The addax has a brown hair tuft extending from the base of its horns to between its eyes. A white patch, continuing from the brown hair, extends till the middle of the cheek. On the other hand, the scimitar oryx has a white forehead with only a notable brown marking a brown lateral stripe across its eyes. It differs from other antelopes by having large, square teeth like cattle, and lacking the typical facial glands.
*information courtesy of https://en.wikipedia.org/wiki/Addax