South America alone is now inhabited by species of sloth, of armadillo, of cavy, aguti, ctenomys, and platyrrhine monkey ; but no fossil remains of a quadruped referable to any of these genera have yet been discovered in Europe, Asia, or Africa. The types of Bradypus and Dasypus were, how ever, richly represented by diversified and gigantic specific Extinct Terrestrial Sloth, Mylodon robustus (Pleistocene, S. America).
forms in South America during the geological periods imme diately preceding the present. The skeleton of one of these forms of the sloth tribe is represented in fig. 134 ; it measures from the fore part of the skull to the end of the tail, 11 feet. It was discovered buried 12 feet deep in the fluviatile depo sits seven leagues north of the city of Buenos Ayres in the year 1841. It forms the subject of a work entitled, Descrip tion of the Skeleton of an Extinct Gigantic Sloth (Mylodon robustus),* in which are set forth in detail the grounds for regarding it as a member of the same natural family as the present small arboreal sloth, and as being modified to obtain its leafy food by uprooting and prostrating trees.
A still larger species of terrestrial sloth (Megatherium) co existed with the Mylodon in South America. Its skeleton, now complete in the British Museum, measures 18 feet ; its dentition Section of upper molar teeth, Megatheriuni (one-third nat. size), Pleistocene, South America.
agrees as to number and kind of teeth with that of the sloths (Bradypus). But the molars (fig. 135) are longer, more deeply implanted, of more complex structure, and with grinding surfaces of the bilophodont type. The elephants, which sub sist on similar food to that of the Megatherium, had their grinding machinery maintained by a numerous succession of teeth : the same end was attained in the Megatherium, by a constant growth and renovation of the same teeth. The for mative pulps were lodged in the deep basal cavities, exposed in the section figured (fig. 135). The molar teeth were five in number on each side of the upper jaw, and four in number on each side of the lower jaw (fig. 136).
In this bone the fore part is much pro longed, and grooved above, to support a long, cylindrical, powerfully muscular tongue, by which the Megatherium, like the giraffe, stripped off the small branches of the trees its colossal strength enabled it to prostrate. The dentition
of Mylodon differed only from that of Megatherium in the shape of the teeth. The same may be said of the allied genera Megalonyx and Seelidoth,erium. They were contemporary and geographi cally associated genera of the same, now quite extinct, family of great terrestrial sloths.
In like manner, the small loricated and banded quadrupeds of South America called armadillos were repre sented in pleistocene times in that continent by as well-defended species, rivalling the Megathe rioids in bulk. The specimen of the almost entire skeleton and bony armour (fig. 137) is one of the smaller species of these great extinct non-banded armadillos ; yet it measures from the snout to the end of the tail, following the curve of the back, 9 feet ; the tesselated trunk-armour being 5 feet in length and 7 feet across, following the curve at the middle of the back. These large extinct species differ from the modern armadillos, in having no bands or joints in their coat of mail, for the purpose of contracting or bending the body into the form of a ball. They also differ in the fluted form of the teeth (fig. l 38) ; whence the generic name (Glyptodon) assigned to them. The species are distinguished, like their present puny representa tives (Dasypus), by peculiar patterns of the outer surface of the constituent ossicles of the tesselated mail. In the species figured (G. elaripes), a large raised central circular plate is surrounded by smaller portions. The species named G. reticulatus, G. tuber =haus, G. ornatus, etc., have their names from other modi fications of the sculptured surface of their armour. Above the principal figure in cut 137 are shown the front and back margins of the body-armour ; below it, opposite the left hand, are upper and under views of the cranium, which was defended by a tesselated bony calque. The tail also had its indepen dent osseous sheath, supported by the vertebra. within, as shown in the figure opposite the right hand.
Macrauchemia,t and Protopithecus,t are addi tional evidences of extinct South American Mammals, matched only by species now peculiar to that continent.