22 
NOTICE OF TEE MEGATHERIUM. 
Horses comes galloping by, closely pursued by the sabre-toothed Lion — the fearful Machairodus. 
A Mastodon, an Ape, and a Dog complete the picture. Such were the animal forms which 
covered the Pampas in the Pleistocene period. We notice with interest their close family alli- 
ance to the genera of Mammalia now inhabiting South America, and the notable differences 
between them and their fossil cotemporaries in the Old World. They are but one illustration 
among many of a general law, deducible from the fossil animals of the eras immediately ante- 
cedent to the human, that, with extinct as with existing Mammalia, particular forms were 
assigned to particular provinces, and that the same forms were restricted to the same provinces 
at a former geological period that they are at the present day. 
We have noticed the numerous monster fossil Edentates which gave place in South Amer- 
ica to the Sloths, Anteaters and Armadillos which are now the characteristic forms of that 
continent. In like manner Australia had its Nototherium, Macropus Titan, Diprotodon, Thy- 
lacoleo, and other forms of herbivorous and carnivorous Marsupials, which represented on a 
huger scale the peculiar fauna which inhabits that continent at the present day. A race of 
gigantic wingless birds — Dinornis, Palapteryx — were in New Zealand, in a period, which 
seems to have blended with the actual one, the lordly prototypes of the strange Apteryx which 
now hides in the thick grass-tufts of that island. The stately Megaceros of Ireland yielded 
its place to the modern Fallow-deer: the Cave-bear of Continental Europe to the smaller 
Brown Bear of the present day. There are indeed some cosmopolite genera, such as the 
Mastodon, the Mammoth, and the Horse, which were simultaneously represented by different 
fossil species over nearly the entire extent of both the eastern and western hemispheres; but 
the few exceptions of this kind by no means invalidate the rule which we have given. 
The former distribution of the Megatheroid animals concurs with other facts in showing us 
that the continents of North and South America did not, at that time form two distinct zool* 
ogical provinces as they do at the present day. They even give us an index of the time when 
the great plateau of Central Mexico was lifted up to its present position, thenceforth to form a 
physicial barrier between the two continents which few animal species could cross. The whole 
period during which these large quadrupeds roamed upon the plains of South America, is far 
shorter than the life-time of their cotemporary invertebrate species; for the same species of marine 
shells which are found imbedded in the very lowest deposits in which the Megatherian remains 
occur, are still living in abundance in the adjacent ocean. There are, moreover, features in 
the constitution of land animals which render them far more obnoxious than are others, to the 
extirpating influences that accompany the changes of general physical conditions which are 
constantly supervening in every country. And also in proportion to the bulk of the animal is 
the difficulty of the contest which, as a living organism, it has to maintain against these des- 
troying agencies. “ Any changes,” says Prof. Owen, in such external agencies as a species 
may have been originally adapted to exist in, will militate against that existence in a degree 
proportionate to the bulk of the species. If a dry season be gradually prolonged, the large 
Mammal will suffer from the draught sooner than the small one; if such alteration of climate 
affects the quantity of vegetable food, the bulky Herbivore will first feel the effects of stinted 
nourishment; if new enemies be introduced, the large and conspicuous animal will fall a prey, 
while the smaller kinds conceal themselves, and escape.”* The early destruction of the Mega- 
therium and its huge congeners must then not surprise us. 
•* Owen on the genus Dinornis ; Trans, of Zool. Soc., vol. iv: p. 15. 
