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Similarly, the American phytophagous giant added to a bilophodont working-surface 

 of its few and small molars, the peculiar texture and rootless condition of the long deeply 

 implanted ever-growing dental mass, characteristic of the molars of the existing dwarf- 

 sloths of its continent. 



When only the large curved pair of upper scalpriform incisors of Diprotodon were 

 known, to which the subcompressed lower pair are opposed, an alliance of Diprotodon 

 to Phascolomys was suggested. The subsequent evidence of a nearer affinity to Macropus 

 instructively exemplifies the superior value of the molar teeth as indicators of the nature 

 of an extinct animal*. 



It is true that in the proportions of the limbs, especially in those of the tibia and its 

 distinction from the fibula, as in some other particulars of the osteology of Diprotodon, 

 it resembles more the Wombats than the Kangaroos ; but the more weighty and essential 

 correspondences are with the Macropodidw ; the equipedal modifications are adaptive 

 and necessitated by the bulk of the extinct marsupial herbivore. The most elastic 

 imagination could hardly stretch to the association of the disproportionate hind limbs of 

 the Kangaroo with a trunk equalling that of a Rhinoceros ; for according to that pattern, 

 Diprotodon must have towered to a height of 30 feet. The departure from the type of 

 its diminutive modern allies is, again, interestingly analogous to that which occurs in the 

 herbivorous Bruta. The bulk and weight of body in Megatherium precluded the pro- 

 portions of length and slenderness, with terminal prehensile instruments, in the limbs, 

 by means of which its diminutive congeners and contemporaries have been enabled to 

 withdraw themselves from an unequal conflict into the safe shelter of lofty trees. In like 

 manner the bulk and weight of Diprotodon militated against its enjoying the privilege of 

 the elongate saltatory limbs to which its small congeners and contemporaries the Kanga- 

 roos have owed their safety, or of the scansorial ones by which the Koala climbs out of 

 danger. 



The analogies traceable between the extinct herbivorous giants of the two remote 

 tracts of dry land are full of interest and instruction. I may add that, as swift and con- 

 tinuous course and power of climbing are privileges checked or regulated by the mass 

 and weight to be hurried along or dragged aloft, so likewise is the faculty of burrowing 

 and concealment under ground. The Diprotodon was as impotent to avail itself of the 

 means of escape to which the comparatively diminutive Wombats owe their present ex- 

 istence, at it was of the interposition of space, which the Kangaroo by a succession of 

 long leaps, rapidly puts between itself and its pursuers. 



Subject to this explanation the combination of Wombat- and Kangaroo-characters 

 may be adduced as exemplifying that more generalized structure in Diprotodon from 

 which, or from some earlier still more generalized marsupial type, may have diverged the 



* Agreeably with the rule laid down by the great Founder of Paleontology ; " La premiere chose a faire 

 dans l'etude d'un animal fossile, est de reconnoitre la forme de ses dents molaires ; on determine par-la, s'il est 

 carnivore ou herbivore, et dans ce dernier cas, ou peut s'assurer jusqu'a un certain point de l'ordre d'herbi- 

 vores auquel il appartient," Cuvlee, Ossemens Fossiles, 4to, vol. hi. 1812, p. 1 (Premier Memoire). 



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