The Geographical Distribution of Animals, Volume 2 / With a study of the relations of living and extinct faunas as elucidating the past changes of the Earth's surface

by Alfred Russel Wallace

The Squirrel family, comprehending also the marmots and prairie-dogs, are very widely spread over the earth. They are especially abundant in the Nearctic, Palæarctic, and Oriental regions, and rather less frequent in the Ethiopian and Neotropical, in which last region they do not extend south of Paraguay. They are absent from the West Indian islands, Madagascar, and Australia, only occurring in Celebes which doubtfully belongs to the Australian region. The genera are as follows:—

Sciurus (100-120 sp., including the sub-genera Spermosciurus, Xerus, Macroxus, Rheithrosciurus, and Rhinosciurus), comprises the true squirrels, and occupies the area of the whole family wherever woods and forests occur. The approximate number of species in each region is as follows: Nearctic 18, Palæarctic 6, Ethiopian 18, Oriental 50, Australian (Celebes) 5, Neotropical 30. Sciuropterus (16-19 sp.), comprises the flat-tailed flying squirrels, which range from Lapland and Finland to North China and Japan, and southward through India and Ceylon, to Malacca and Java, with a species in Formosa; while in North America they occur from Labrador to British Columbia, and south to Minnesota and Southern California. Pteromys (12 sp.), comprising the round-tailed flying squirrels, is a more southern form, being confined to the wooded regions of India from the Western Himalayas to Java and Borneo, with species in Formosa and Japan. Tamias (5 sp.), the ground squirrels, are chiefly North American, ranging from Mexico to Puget's Sound on the west coast, and from Virginia to Montreal on the Atlantic coast; while one species is found over all northern Asia. Spermophilus (26 sp.), the pouched marmots, are confined to the Nearctic and Palæarctic regions; in the former extending from the Arctic Ocean to Mexico and the west coast, but not passing east of Lake Michigan and the lower Mississippi; in the latter from Silesia through South Russia to the Amoor and Kamschatka, most abundant in the desert plains of Tartary and Mongolia. Arctomys (8 sp.), the marmots, are found in the northern parts of North America as far down as Virginia and Nebraska to the Rocky Mountains and British Columbia, but not in California; and from the Swiss Alps eastward to Lake Baikal and Kamschatka, and south as far as the Himalayas, above 8,000 feet elevation. Cynomys (2 sp.), the prairie-dogs, inhabit the plains east of the Rocky Mountains from the Upper Missouri to the Red River and Rio Grande (Plate XIX., vol. ii. p. [129]). Anomalurus (5 sp.), consists of animals which resemble flying-squirrels, but differ from all other members of the family in some points of internal structure. They form a very aberrant portion of the Sciuridæ, and, according to some naturalists, a distinct family. They inhabit West Africa and the island of Fernando Po.

Extinct Sciuridæ.—These are tolerably abundant. The genus Sciurus appears to be a remarkably ancient form, extinct species being found in the Miocene, and even in the Upper Eocene formations of Europe. Spermophilus goes back to the Upper Miocene; Arctomys to the Newer Pliocene. Extinct genera are, Brachymys, Lithomys and Plesiarctomys, from the European Miocene, the latter said to be intermediate between marmots and squirrels.

In North America, Sciurus, Tamias, and Arctomys occur in the Post-pliocene deposits only. The extinct genera are Ischyromys, from the Upper Miocene of Nebraska; Paramys, allied to the marmots, and Sciuravus, near the squirrels, from the Eocene of Wyoming.

Here we have unmistakable evidence that the true squirrels (Sciurus) are an Old World type, which has only recently entered North America; and this is in accordance with the comparative scarcity of this group in South America, a country so well adapted to them, and their great abundance in the Oriental region, which, with the Palæarctic, was probably the country of their origin and early development. The family, however, has been traced equally far back in Europe and North America, so that we have as yet no means of determining where it originated.

Family 62—HAPLOODONTIDÆ.—(1 Genus, 2 Species.)

General Distribution.
Neotropical Sub-regions.	Nearctic Sub-regions.	Palæarctic Sub-regions.	Ethiopian Sub-regions.	Oriental Sub-regions.	Australian Sub-regions.
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The genus Haploodon or Aplodontia, consists of two curious rat-like animals, inhabiting the west coast of America, from the southern part of British Columbia to the mountains of California. They seem to have affinities both with the beavers and marmots, and Professor Lilljeborg constitutes a separate family to receive them.

Family 63.—CHINCHILLIDÆ. (3 Genera, 6 Species.)

General Distribution.
Neotropical Sub-regions.	Nearctic Sub-regions.	Palæarctic Sub-regions.	Ethiopian Sub-regions.	Oriental Sub-regions.	Australian Sub-regions.
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