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middle Eocene to Recent
|A southern short-tailed shrew|
Although its external appearance is generally that of a long-nosed mouse, a shrew is not a rodent, as mice are. In fact it is related to moles. Shrews have sharp, spike-like teeth, not the familiar gnawing front incisor teeth of rodents.
Shrews are distributed almost worldwide. Of the major tropical and temperate land masses, only New Guinea, Australia, and New Zealand do not have any native shrews. In South America, shrews are relatively recent immigrants and are present only in the northern Andes. In terms of species diversity, the shrew family is the fourth most successful mammal family.
All shrews are small, most no larger than a mouse. The largest is the Asian house shrew (Suncus murinus), which is about 15 cm long and weighs around 100 grams. Several are very small: the Etruscan shrew (Suncus etruscus), is about 3.5 cm and 2 grams. It is the smallest living terrestrial mammal.
In general, shrews live in and on the ground. They search for seeds, insects, nuts, and worms. Some climb trees, some live underground, some live under snow, and some hunt in water. They have small eyes, and generally poor vision, but have excellent senses of hearing and smell. They are very active animals, with big appetites. Shrews have an unusually high metabolic rate. Shrews usually eat 80–90% of their own body weight in food daily.
Unlike rodents, which have gnawing incisors that grow throughout life, the teeth of shrews wear down throughout life, and they lose their milk teeth before birth. Therefore they have only one set of teeth for their lifetime. Apart from the first pair of incisors, which are long and sharp, and the chewing molars at the back of the mouth, the teeth of shrews are small and peg-like, and may be reduced in number. The dental formula of shrews is:upper=3.1.1-3.3; lower=1-2.0-1.1.3.
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