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Updated: May 1, 2025
Small mammals are often of much greater interest and importance scientifically than large ones, for, especially among the Insectivores, there are many primitive forms which are apparently of ancestral stock and throw light on the evolutionary history of other living groups.
Nay, even foxes, which, as a rule, live isolated in our civilized countries, have been seen combining for hunting purposes. Even some bears live in societies where they are not disturbed by man. Thus Steller saw the black bear of Kamtchatka in numerous packs, and the polar bears are occasionally found in small groups. Even the unintelligent insectivores do not always disdain association.
Perhaps the more common opinion is that they were evolved from a branch of the Insectivores, but the evidence is too slender to justify an opinion. It was an age when the primitive placental mammals were just beginning to diverge from each other, and had still many features in common.
These in turn enter the scene quite suddenly, and the authorities are reduced to uncertain and contradictory conjectures as to their origin. Some think that they develop not from the femurs, but along an independent line from the Insectivores, or other ancestors of the Primates.
These primitive mammals help us to reconstruct the mammal life of the Mesozoic Epoch. The bones that we have are variously described in geological manuals as the remains of Monotremes, Marsupials, and Insectivores. On the other hand, the lower jaw of the Marsupial is characterised by a peculiar hooklike process, and this is commonly found in Mesozoic jaws.
In the Oligocene we find primitive squirrels, beavers, rabbits, and mice. The Insectivores also developed some of the present types at an early date, and have since proved so unprogressive that some regard them as the stock from which all the placental mammals have arisen. Some specimens of it are seventy feet in length.
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