Aardvarks and subungulates

Plant-eating mammals that possess hoofs are referred to as ungulates. But many nonhoofed animals have evolved from primitive ungulate ancestors and have features that are similar to the ungulates. Consequently, they are called subungulates. Subungulates include the aardvark, elephants, manatees, and conies.

The subunguiates, shown here to scale, have a wide variety of forms and sizes. But they are classified together mainly because of their teeth.

Aardvarks

As the only surviving species of primitive ungulates, the aardvark is classified in an order by itself the Tubulidentata. The name relates to the aardvark’s unusual molar teeth, which contain many tubular pulp cavities.

Aardvarks are found in the savanna regions of Africa. Their name means “earth pig” in Afrikaans, a Dutch dialect spoken in South Africa, and refers to the aardvark’s appearance and burrowing habits. These animals are stocky and powerful, weighing up to 140 pounds (64 kilograms). They have large ears that flatten to keep out the soil when they are burrowing. They have strong limbs and a thick, muscular tail. Aardvarks resemble the anteaters of South America in several ways— both have an elongated snout, no teeth, and a long tongue that they can extend from their mouths. These features reflect parallel adaptations to a similar diet.

Aardvarks feed mainly on ants and termites, using their strong claws to break open sunbaked ant and termite hills. They also collect the insects as they swarm across the ground. An aardvark’s tongue is covered with sticky saliva, to which the insects adhere, and the aardvark can extend its tongue up to 18 inches (46 centimeters). Their thick skin appears to protect them from the bites of termites.

They are nocturnal, traveling upto 19 miles (30 kilometers) every night in search of termites. During the day, they sleep in their burrows. They usually have single offspring, but occasionally produce twins.

Elephants

The present order of elephants (Proboscidea) is a mere remnant of its former size. In the Ice Age, numerous species, which included the mammoths, were spread throughout the world. Today, only one family remains (Elephantidae), containing two species—the African elephant and the Asiatic, or Indian, elephant. They are easily distinguished from each other because the African species has larger ears than its Asian counterpart and grows bigger. The African elephant is the largest living land animal, weighing up to 6 short tons (5.4 metric tons). To support their weight, the limbs of elephants have become pillarlike, with each bone resting directly on the one below. Each foot has a thick pad of tissue that acts as a cushion against the elephant’s weight.

Elephants often consume more than 770 pounds (349 kilograms) of vegetable matter per day and may spend up to 16 hours a day feeding. Elephants use their trunk, which is an extension of the nose and upper lip, to collect food and water. At the trunk tip are fingerlike projections (one in the Asiatic elephant and two in the African), which allow the trunk to pick up objects as small as peanuts. Most of their food is woody and fibrous, and is broken down by very large molar teeth with jagged ridges. Each jaw has six molar teeth per side, but normally only one tooth is present at a time. As the tooth wears away, another one erupts from the back of the jaw. Once the elephant loses the last tooth, it has difficulty feeding and may starve. The much sought after ivory tusks of elephants are not canines, as is often thought, but rather well developed upper incisors. Tusks of more than 10 feet (3 meters) long are known to have been taken from African bull elephants.

Conies

Conies, or hyraxes, are agile climbers, both on rocks and in trees. This rock hyrax keeps a lookout for possible predators while the rest of its colony basks in the sun.

Conies, or hyraxes, (order Hyracoidea) resemble large, gray-brown guinea pigs. But they are more closely related to elephants than to rodents, particularly in the arrangement of their teeth. Conies have well developed grinding cheek teeth, and upper incisors that grow continually and protrude from the mouth. These teeth are equivalent to tusks in elephants. The cony digestive system is unusual in that it has two appendixes.

Rock conies are highly sociable animals and they live in large colonies. They are active during the day and often bask in the sun, while older members of the colony act as lookouts. These sentries give a shrill alarm call if a predatory animal, such as a leopard, bird of prey, or python, approaches. Tree conies are less sociable than rock conies and are nocturnal, spending the day in tree holes or foliage.

All conies are highly vocal and use a wide range of croaks, cries, and alarm calls. All species also have a gland on the back, which is marked by a patch of different colored hair. This gland is exposed whenever the surrounding hairs stand erect—during the mating season or when the cony is frightened, for example. The gland is used to mark territory.

African elephants roam in herds consisting mainly of females and juveniles. After a gestation period of 18 to 23 months, pregnant females leave the herd to give birth. Like other mammals, the newborn young are fed on milk. The female has two nipples, which are located between her front legs.

Manatees, dugongs, and sea cows

Despite their large, blubber-filled bodies, this group (order Sirenia) is thought to have been the source of the mermaid stories. These aquatic mammals live in coastal waters and large river systems in tropical and subtropical areas. Weighing up to 1,500 pounds (680 kilograms) and ranging in size from about 6 to 13 feet (2 to 4 meters) long, they never venture ashore. Today there is one genus of manatees (Trichechus), which contains three species, and one genus of dugongs and sea cows (Dugong), of which only dugongs exist. Sea cows became extinct in the mid-1700’s after sailors killed them off for food.

Sirenians feed on seaweeds or freshwater plants. In Guyana, manatees have been used to control water weeds, which would otherwise choke up the rivers. The dugong has tusklike incisors and three cheekteeth on each side, whereas the manatee has no incisors, but up to 10 cheek teeth on each side, which are replaced and move forward continually.

The forelimbs of manatees form paddles, as in many other aquatic mammals. There are no hind limbs, and the tail has a horizontal fluke similar to a whale’s. Manatees can remain submerged for up to 15 minutes at a time.

Elephants, conies, and dugongs all eat plants and have a series of cheek teeth for grinding plant material. A cony has rodentlike incisors, but in elephants and dugongs the upper incisors are modified into tusks. A manatee has neither incisors nor tusks.