Imágenes de páginas
PDF
EPUB

Toxodon, a member of a peculiar extinct family of Ungulates.

The occurrence of all these animals indubitably proves that now for the first time a connection had been formed between the continents of North and South America. Before this epoch, no trace of a Neotropical admixture can be anywhere detected in the Nearctic mammal-fauna.

Thus the evidence of palseontology in every way supports the deductions drawn from a study of the distribution of recent forms, namely, that the bulk of the present Nearctic fauna has been mainly derived from the Old World, although at times the Region has been sufficiently isolated and sufficiently extensive for the independent evolution of its own characteristic forms. In accordance with these deductions, the present remaining inhabitants of the Nearctic Region may be divided into three categories, as follows: (1) The Endemic Fauna, the bulk of which has had, at some considerably remote geological period, a common origin with that of the Palaearctic Region, although it has enjoyed ample time to develop and differentiate itself on its own lines. (2) A Neotropical constituent, which first appeared in the Nearctic Region in Pliocene times. (3) A comparatively modern Palsearctic fragment, in which not only the genera, but frequently the species, are identical in both Regions. This portion of the fauna has probably reached the Nearctic Region by the passage which must have existed in comparatively modern times across Behring Straits. Consequently, while the Neotropical element is the stronger in the south, this last, the Pahearctic element, is far more prevalent in the extreme north.

List Of The Principal Authorities Referred To
In Chapter VI.

(1) Allen, J. A.—" The Geographical Distribution of North American Mammals." Bull. Amer. Mug. Nat. Hist., iv., p. 199. 1892.

(2) Merriam, C. H.—" The Geographical Distribution of Life in North America, with Special Reference to the Mammalia." Proc Biol. Soc. Washington, vii., p. 1. 1892.

(3) Zittel, Karl Von.—"The Geographical Development, Descent, and Distribution of the Mammalia." Geol. Mag., 3rd ser., x., p. 401. 1893. (Translated from the S. B. k. Bayer. Akad. Wiss., xxiii., p. 137. 1893).

CHAPTER VII

THE PAL^EARCTIC REGION
(plate VII., p. 196)

Section L—Boundaries Of The Pal^earctic Region

This, the last of the six great Regions, consists, as its name implies, of the whole northern part of the Old World. Its boundaries have already been defined in previous articles dealing with the Ethiopian and Oriental Regions, these being the only Regions with which it marches. Speaking generally, it may be said to consist of the whole of Europe, the northern border of Africa, and Asia north of the Himalayas. Its southern boundary in Africa was taken, in the article on Ethiopia, as the Tropic of Cancer, but this, of course, is a purely arbitrary line, and runs through the centre of the Sahara Desert. It would, perhaps, be more accurate to put in its place the northern edge of the Sahara as the limit, and to include all the desert country both of Africa and Arabia in the Ethiopian Region.

The question of Egypt is a difficult one, as its fauna undoubtedly contains a mixture of forms characteristic of both the Palsearctic and Ethiopian Regions; on the whole, however, Egypt, up to the First Cataract, is best included in the Palaearctic Region.

In regard to the boundary line between the Pahearctic and Oriental Regions, there can be no doubt that at the higher elevations of the Himalayas a true Palaearctic fauna

'177 M

« AnteriorContinuar »