The common tsessebe or sassaby (Damaliscus lunatus lunatus) is the southern, nominate subspecies of Damaliscus lunatus, although some authorities have recognised it as an independent species. It is most closely related to the Bangweulu tsessebe, sometimes also seen as a separate species, less to the topi, korrigum, coastal topi and tiang subspecies of D. lunatus, and less to the bontebok in the same genus. Common tsessebe are found in Angola, Zambia, Namibia, Botswana, Zimbabwe, Eswatini (formerly Swaziland), and South Africa.
Common tsessebe are among the fastest antelopes in Africa and can run at speeds up to 90 km/h.
Adult tsessebe are 150 to 230 cm in length They are quite large animals, with males weighing 137 kg and females weighing 120 kg, on average. Their horns range from 37 cm for females to 40 cm for males. For males, horn size plays an important role in territory defense and mate attraction, although horn size is not positively correlated with territorial factors of mate selection. Their bodies are chestnut brown. The fronts of their faces and their tail tufts are black; the forelimbs and thigh are greyish or bluish-black. Their hindlimbs are brownish-yellow to yellow and their bellies are white. In the wild, tsessebe usually live a maximum of 15 years, but in some areas, their average lifespan is drastically decreased due to overhunting and the destruction of habitat.
The most significant difference between the tsessebe, the southernmost subspecies, and the other topi subspecies is the incline of the horns, with the tsessebe having horns which are placed further apart from each other as one moves distally. This has the effect of the space between them having a more lunate profile when seen from a certain angle, as opposed to lyrate, more like that of a hartebeest. Tsessebe populations show variation as one moves from South Africa to Botswana, with southerly populations having on average the lightest pelage colour, smallest size and the least robust horns. Common tsessebe do not differ significantly from the Bangweulu tsessebe, the northernmost population, but in general the populations from that part of Zambia are on average the darkest-coloured and have the most robust horns, although differences are slight and individuals in both populations show variation in these characteristics which almost completely overlap each other.
Tsessebe are social animals. Females form herds composed of six to 10, with their young. After males turn one year of age, they are ejected from the herd and form bachelor herds that can be as large as 30 young bulls. Territorial adult bulls form herds the same size as young bulls, although the formation of adult bull herds is mainly seen in the formation of a lek. Tsessebe declare their territory through a variety of behaviors. Territorial behavior includes moving in an erect posture, high-stepping, defecating in a crouch stance, ground-horning, mud packing, shoulder-wiping, and grunting.
