The proboscideans flourished throughout the first half of the Cenozoic, but with humankind's appearance their numbers fell until they had almost become extinct. A few genera only, such as Elephas and Loxodonta, were latterly contemporaries of humans and both of these died out shortly before humanity's disappearance, leaving no descendants. The ecological niche which they vacated was eventually filled by the descendants of a surviving group of antelopes, the gigantelopes. These enormous creatures with short legs and weighing up to ten tonnes became the giant herbivores of the tropical plains, a group of animals feeding on trees, grasses or roots depending on the species. They had long since abandoned the antelope's running gait and had instead taken up a plodding existence - the two-toed feet of their ancestors having become broad-hooved pads.
The gigantelopes' immediate ancestors had long, double-pointed antler-like horns. In some, the rear portions disappeared, leaving long forward-pointed prongs.
The animal's basic shape was highly successful and in the course of time the gigantelopes spread northwards from tropical Africa, crossing the Himalayan Uplands in two separate waves of migration; one spreading into the coniferous forests and giving rise to the hornheads, and the other, much later, reaching the tundra and providing the ancestors of the woolly gigantelope, Megalodorcas borealis.
Once the massive body of the gigantelope had been established a number of variations appeared. The earliest was the long-necked gigantelope, Grandidorcas roeselmivi.
The tropical gigantelope and rundihorn are representative members of a group of mostly tropical, heavy grazing bovids that are descended from the antelope.
Tropical Gigantelope, Megalodorcas giganteus, the typical tropical grassland-dwelling type of gigantelope from Africa. It has four horns (one pair curving down behind its ears and another pair pointing out in front of its snout). Each horn has a pick-like point, enabling the animal to scrape soil away from the plant roots and bulbs on which it feeds. It is about 3.3 meters high at the shoulder and weighs 10 tonnes. At first glance these massive beasts seem to contradict the general rule that animals of hotter climates tend to be smaller than their equivalents in cooler areas. The larger an animal is, the smaller its surface area is in relation to its body mass, and the more difficult it is for it to lose excess heat. In the case of tropical gigantelopes, however, this problem is overcome by the possession of a large dewlap beneath the neck, which is well served with blood vessels and effectively increases the creature's body area by about a fifth, thus providing an efficient heat radiator. Its principal predator is the horrane.
Rundihorn, Tetraceras africanus, an African gigantelope from tropical grasslands that is almost the direct equivalent of the extinct rhino. It has adopted a body size (about 1.8 meters high at the shoulder and 4 tonnes in weight) and a horn arrangement not unlike its predecessor's and is a grazing animal, a fact that is reflected by its broad snout and muzzle. Its alarming horn array is used for defense, although the animal has few enemies likely to risk a frontal attack. For the males, however, its secondary function (for sexual display) is now more important.
Long-Necked Gigantelope, Grandidorcas roeselmivi, an almost
The long-necked gigantelope is a browser and eats the leaves and shoots of trees. It has two vestigial horns, no more than bony pads on the top of the head.
primitive-looking African tropical grassland species. It is able to browse on twigs and branches 7 meters above the ground, well out of reach of the smaller herbivores and even of its own massive cousins. Like the woolly gigantelope, it is about 3 meters high at the shoulder and weighs 7.5 tonnes. As well as a long neck this animal also has a long, narrow head, enabling it to push its thick muscular lips between the branches of the trees to reach the tastiest morsels. The horns of its ancestors are reduced to long, low, bony pads at the top of the skull. Anything more elaborate would become entangled in the branches.
Unlike most members of the gigantelope family, long-necked gigantelopes are not herd animals. They are typically found in ones and twos in lightly wooded areas around the margins of the tropical forests of Africa.
Shovel-Horned Gigantelope, a recently
Until recently the shovel-horned gigantelope was found on the African tropical and temperate grasslands. It is thought to have lived near rivers and lakes, and to have fed mainly on water plants.
