PROFESSOR OWEN ON THE FOSSIL MAMMALS OF AUSTRALIA. 
567 
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 Diprotodo7i 
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 Macropodidoe’, 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 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, have diverged the 
* Agreeably with the rule laid down by the great Founder of Palaeontology ; “ La premiere chose a faire 
dans P 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,” Ctjviek, Ossemens Fossiles, 4to, vol. iii. 1812, p. 1 (Premier Memoire). 
4 H 
M DCCCLXX. 
