Fig. 300.—Small predaceous marsupial (†Cladosictis lustratus) and rabbit-like †typothere (†Pachyrukhos moyani), Santa Cruz stage. Restored by C. Knight from skeletons in Princeton University and the American Museum of Natural History.
Suborder Diprotodonta
North America never had any representatives of this suborder, but South America possessed many of them in the Santa Cruz Miocene and one genus (Cænolestes) has survived to the present time. Australia, on the other hand, has three well-defined families of the suborder, the kangaroos, phalangers and wombats, but no member of any of these has ever been found outside of the Australian region. So far as we know, therefore, the suborder is and always has been confined to the southern hemisphere.
Fig. 301.—Skull of Cænolestes obscurus, enlarged. (After Sinclair.)
The modern South American genus Cænolestes is a small, rat-like animal and very rare; it has been found only in Ecuador and Colombia. Its dentition is not at all typically diprotodont, but rather intermediate in character between the latter and the Polyprotodonta. The dental formula is: i 4/3, c 1/1, p 3/3, m 4/4, × 2 = 46. The upper incisors are small and of subequal size, though the second is somewhat the largest of the series, and the canine is considerably larger and more prominent than any of them. The foremost lower incisor is long and pointed and directed almost straight forward; the other lower incisors and the canine are minute and can have little or no functional value. The premolars are small and simple and the upper molars quadritubercular, the third one triangular, and the fourth very small and apparently about to disappear. Such teeth would seem to indicate a vegetable diet, but it is reported that the animal subsists chiefly upon small birds and their eggs. The skull, which is typically marsupial in all its characters, is most like that of the smaller Australian native cats (Dasyuridæ) and the feet show no signs of the syndactyly which all the other diprotodonts display so clearly. Dr. Gregory is “inclined to regard Cænolestes and its allies as an independent suborder, an offshoot of primitive Polyprotodonts which has paralleled the Diprotodonts in certain characters of the dentition.”[21]
Fig. 302.—Lower jaws of Santa Cruz cænolestids, enlarged. A, †Garzonia patagonica. B, †Abderites crassignathus. C, †Callomenus ligatus. (After Sinclair, in Reports Princeton University Expeditions to Patagonia, Vol. IV.)