The Insectivora is probably the most ancient order of placental mammals. These insect-eating mammals are known to have lived as far back as 100 million years ago, sharing their world with dinosaurs. They all share certain basic features, but each species has specialized for a different way of life so that they are superficially dissimilar.
With bats (order Chiroptera), which are generally considered to be descended from Insectivora stock, flying lemurs (Dermoptera), anteaters, sloths and armadillos (Edentata), pangolins (Pholidota) and some primates, they form the bulk of a large group of mainly insect-eating mammals.
Classification of Insectivores
Today, Insectivora is the third largest order of mammals, comprising 4 suborders and about 360 species. The suborder Lipotyphla contains most of insectivores, and includes mouselike creatures such as solenodons, tenrecs, moles, desmans and golden moles; hedgehogs, moonrats and shrews. The related water- or otter-shrews have been placed in their own suborder, Zalambdodontia, because their teeth differ from the rest of the insectivores. The elephant-shrews have also been separated into the suborder Macroscelidea, for the reason that they hop on their back legs. The suborder Dermoptera contains the flying lemur, the most accomplished of gliding mammals. Insectivores include ground-living, burrowing, climbing and even semiaquatic species. They feed on insects, grubs and snails and, occasionally, on helpless vertebrates such as the young of ground-nesting birds. Many insectivores are extremely active and therefore need to be refueled constantly by large quantities of food, sometimes equaling the animal's total body weight each day.
Insectivores occur throughout the world except for Australia, New Zealand and some oceanic islands. Typically they are small, nocturnal mammals with elongated narrow snouts. They are distinguished from other small mammals by the fact that they have 5 digits on each limb; rodents, for example, have 4 or less. Each digit has a distinct claw. The body is covered with short, dense fur; in some species, such as hedgehogs and tenrecs, some of the hairs are developed into spines. They have small ears and small eyes with poor vision; their senses of smell and hearing, however, are usually sharp.
The brain has a primitive structure and the placenta is simpler than that found in most other placental mammals. These usually have sharp cusps which enable them to slice their prey.
Habitats and Life Styles
The Tenrec family (Tenrecidae) includes about 20 species, all found on Madagascar and the Comoro islands. They are primitive animals and retain some reptilian features. Some resemble shrews; those of the genus Setifer resemble hedgehogs and have sharp spines; others are similar to mice and moles. Their main diet consists of small invertebrates and plant material.
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The family Talpidae consists of about 29 species of mole, shrew-mole and desman, which occur widely in the Northern Hemisphere. Most are burrowers and are highly modified for an underground existence with powerful spadelike front feet, minute eyes with poor vision hidden in the fur, and no external ears. The desmans, which are the largest of this group, lead a semiaquatic life in, or near, ponds and streams, and feed on aquatic invertebrates and fish. They use their long noses as snorkels, turning them up so that they stick out of water.
The shrews of the family Soricidae are the most successful insectivore group in terms of numbers; there are about 250 species living almost everywhere in the world. Most are small; the pygmy shrew (Microsorex hoyi) is the smallest and weighs less than 2.5 grams.
Armadillos, Anteaters and Sloths
The order Edentata today contains only 29 species in 3 families: armadillos, anteaters and sloths. All have reduced number of teeth, or none at all. The 20 species of armadillo of the New World are nocturnal and feed primarily on insects as well as other small invertebrates and vertebrates and, in some cases, carion. Their bodies are protected by an armor of horny plates on the skin, leaving only the limbs and underside vulnerable to attackers. Some species of armadillo curl up into a ball to protect these parts of the body. Anteaters are highly specialized on eating ants an termites. The 5 species of sloth are so adapted to life in the trees that they can barely move on land. These creatures have earned their name from their slow movements. for this reason they rarely descend to the ground for they would make easy prey. They live in forests in Central and South America.