When first seen by Europeans it contained no mammals except a large fruit-eating bat (Pteropus vulgaris), which is plentiful in the woods; but several mammals have been introduced, and are now numerous in the uncultivated region.
It may also be noticed that in mammals and birds which hop on two legs, such as jerboas, kangaroos, thrushes and finches, the proportionate length of the thigh-bone or femur to the tibia and foot (metatarsus and toes) is constant, being 2 to 5; in animals, on the other hand, such as hares, horses and frogs, which use all four feet, the corresponding lengths are 4 to 7.
Early trained as a comparative anatomist, the discovery of Upper Eocene mammals in the gypsum quarries of Montmartre found him fully prepared (1798), and in 1812 appeared his Recherches sur les ossemens fossiles, brilliantly written and constituting the foundation of the modern study of the extinct vertebrates.
Thus Huxley, with true prophetic instinct, found that the sum of primitive characters of all the higher placental mammals points to a stem form of a generalized insectivore type, a prophecy which has been fully confirmed by the latest research.
In strong contrast to the poverty of Brazil in the larger mammals is the astonishing profusion of insect life in every part of the country.
With the exception of the Cetacea, most of the Edentata, and the Sirenia, in which the teeth, when present, have been specialized in a retrograde or aberrant manner, the placental mammals as a whole have a dentition conforming more or less closely to the foregoing type.
Among its characteristic mammals and birds are the lynx, marten, porcupine, northern red squirrel, Beldings and Kennicotts ground squirrels, varyin and snowshoe rabbits, northern jumping mouse, white-throate sparrow, Blackburnian warbler, Audubon.
Bison no longer roam the plains, and the elk has been driven out; but among the larger mammals still to be found in certain districts are the deer, prong-horn (in small numbers), puma, coyote, timber wolf, lynx (Lynx rufus and Lynx Canadensis) and the black and grizzly bear.
The same deposits have yielded remains of small mammals whose dentition approximates more nearly to that of either polyprotodont marsupials or insectivores; and these may be conveniently noticed here without prejudice to their true affinities.
Engler, Entwickelungsgeschichte der Pflanzenwelt; also Beddard, Zoogeography (Cambridge, 1895); and Sclater, The Geography of Mammals (London, 1899).