380 VIEW OF THE FAUNA OF BRAZIL 



tions, have brought to light some isolated specimens of its 

 scattered remains ; while, on the contrary, the existent crea- 

 tion presents itself of its own accord to our eye, so that sooner 

 or later it must be the entire property of science. We may, 

 therefore, consider the list of existing species in that class of 

 animals of which we are now speaking, as almost complete ; 

 whereas we may expect with every day an increase to the 

 catalogue of extinct species. 



This poverty of animal forms, that had hitherto been ima- 

 gined to mark the tropical zone, was endeavoured to be ex- 

 plained by the supposition of an extraordinarily high temper- 

 ature, that prevented the development of animal life. We 

 now know that this supposition, and the facts on which it was 

 grounded, are equally without foundation. The tropical zone 

 enjoyed at that period a temperature which not only did not 

 prevent the development of animal life, but was even far 

 more favourable to it than that which it at present possesses. 

 If we have a right to suppose that the richness and variety 

 of organic productions, and their development with regard 

 to size, are in proportion to temperature, — a proposition 

 which is generally received, and when viewed on a large scale 

 is confirmed by experience, — then undoubtedly we cannot 

 but ascribe a higher temperature to that zone in ancient 

 times than it now enjoys ; but this excess of heat is yet 

 much less than what naturalists were hitherto disposed to 

 claim for it on the foundation of an incorrect fact. 



It would be an important task to compare the extinct 

 mammals of tropical America with the correspondent fauna 

 of the temperate and frigid zones of the same continent. But 

 unfortunately the insufficiency of our materials prevents us 

 from instituting any such comparison. Our knowledge of 

 the fauna inhabiting the corresponding zones in the Old 

 World is much more complete ; but even there several cir- 

 cumstances forbid a direct comparison. In the first place, 

 the tropical zone in the Old World, at the present time, is 

 richer in species of mammals than the same region in the 

 New World. In the second place, the extent of country 

 through which the fossils belonging to the former age of the 

 earth have been sought for on the old continent, is infinitely 

 greater than the district in which I have had the opportunity 

 of pursuing my investigations. In the third place, the length 

 of time during which the fossils have been collected in the 

 Old World, and the number of scientific collectors interested 

 therein, are both very considerable ; whereas the description 

 here attempted of the extinct fauna of S. America is the 

 fruit of two years' labour of a solitary individual. Taking 



