Fig. 298.—Skull of †Borhyæna, Santa Cruz. (After Sinclair, Reports Princeton University Expeditions to Patagonia, Vol. IV.)
Fig. 299.—Skull of small predaceous marsupial (†Amphiproviverra manzaniana), showing the punctured wound from a bite. Princeton University Museum.
Associated with these larger predaceous marsupials were several much smaller kinds, ranging in size from a fox to a weasel, which must have preyed upon the abundant rodents and other small mammals and birds. One of these (†Amphiproviverra) had an opposable hallux, somewhat as in the opossums, and was therefore probably arboreal. An interesting specimen in the museum of Princeton University illustrates the pugnacity of these small creatures; it is a skull in which the left upper canine was completely torn out, the circular puncture of the enemy’s bite being unmistakable and the healed edges of the wound proving that the loss of the tooth was suffered during life. In structure, these smaller animals differed so little from the larger ones, that no particular description of them is needed. In the restoration of †Cladosictis ([Fig. 300]) the spotted pattern of the Australian dasyures, or native cats, has been taken as a model.
In the Deseado formation the predaceous marsupials have been less abundantly found than in the Santa Cruz and there can be little doubt that the group is very inadequately represented by the material so far collected. Only two genera, known from lower jaws, have been described, but one of these (†Proborhyæna) is of interest because of its enormous size, far surpassing any of the Santa Cruz forms and equalling the largest modern bears. This is another illustration of the unusual relationship between the Deseado and Santa Cruz faunas, the older stage so frequently having the larger animals.
Predaceous marsupials of small size may be traced back to the Casa Mayor formation, but very little is yet known of them. There is no obvious difficulty in the way of their derivation from opossum-like forms, such as are found in the Cretaceous of North America and probably of South America also.
The relation of the South American to the Australian marsupials offers problems of unusual interest, a discussion of which would be impracticable here. Several alternative solutions of the problem have been offered and great differences of opinion exist with regard to it. To my mind the most probable suggestion is that a land-connection, by way of the Antarctic continent, existed in early Tertiary times, by means of which the ancestors of the Australian marsupials migrated, from South America, though this explanation is rejected by several eminent authorities.