The fibula is a very slender bone, with the distal end swollen and heavy. As it rises from the carpus it is so twisted that it unites with the upper end of the tibia almost on the posterior surface.
| Fibula, | diameter of the articular end | 17 mm. |
| Fibula, | least diameter of the shaft | 10 mm. |
The calcaneum is of moderate length, and very stout, resembling that of Adinotherium, except that it is longer.
| Calcaneum, | length | 64 mm. |
| Calcaneum, | width | 28 mm. |
Of the hind foot there is preserved only the distal portions of two metatarsals, which are about the same size and character as those of the front foot, and a phalanx of the first row, also similar to the same one of the front foot.
[Figure 65] gives a restoration of the animal based on the bones described in the foregoing pages. The animal in all features turns out a typical toxodont, adapted, by the cropping teeth, and the broad-faced premolars and molars, for a grazing animal, but its advancement in adapting itself to feeding on grass has not proceeded very far, as is indicated by the shortness of the molars. The legs are longer than in the other families of the toxodonts which would signify that it had developed some speed, but the feet have progressed toward the modification of the hoofs into claws, indicating a foot more like that of a dog, in which the weight is not carried on the ungual phalanges, but rather on the ball of the foot, or bases of the metapodials.
Fig. 65. (Half tone.) Restoration of Rhynchippus equinus,
Ameghino—⅙ natural size.
I should not feel that this group was the ancestral one to later groups of toxodonts, but it seems rather to represent a line which terminates in the Deseado or very little later, not having run up into the Santa Cruz. The line of ancestry for the toxodonts is rather through Leontinidae.