Fig. 117. Anterior face of the humerus—
⅕ natural size.
For the hind limb I give some of the figures which Gaudry gives accompanying his illustrations of the hind limb.
| Femur, length | 630 mm. |
| Femur, greatest proximal diameter | 240 mm. |
| Femur, distal diameter | 170 mm. |
| Tibia, length | 370 mm. |
| Tibia, greatest proximal diameter | 164 mm. |
| Tibia, greatest distal diameter | 114 mm. |
| Astragulus, antero-posterior diam. | 123 mm. |
| Astragulus, transverse diam. | 114 mm. |
| Astragulus, height | 65 mm. |
CHAPTER XIII
Rodentia
While all of small size, numerically the rodents make about a third of our collection, the number of genera and species being, however, relatively small. All are hystricomorphs with the pattern on the crowns of the teeth relatively simple. While the incisors are typically rodent-like, permanently growing teeth, the molars are all rooted, some being entirely brachydont, others beginning to show hypsodont features.
So far as yet known, the rodents make their first appearance in South America, in this Deseado formation. Were they, as Ameghino thought, developed there from such a form as Propolymastodon or Promysops of the Casamayor formation? Or did they migrate into Patagonia from some other section? For the former proposition to be convincing to me, it would require more complete material of the forms suggested than now exists.[20] Other groups of hystricomorphs occur in the Theridomyidae of the European Oligocene, and from the Oligocene of the Fayum.[21] Either the old world forms are descended from the South American forms, or vice-versa. The two African lower jaws are very much like those of Cephalomys, and my feeling is that the Patagonian forms are derived from some immigrant reaching that section before Deseado times.
The Deseado genera are not widely different from each other, but it is evident that they are the representatives of at least two families, and my expectation is that other families will be found eventually to be already represented.
Our material does not permit the discussion of the skeleton or even of the skull as a whole, for the specimens occur only as isolated jaws, palates, or even as isolated teeth. In a few cases, the upper and lower dentitions are associated, but in no case was skeleton material clearly associated with the teeth. The remains look very much like such as are often found today in the western United States under a hawk’s nest or below the roosting place of owls. I think most of our specimens passed, before burial, through the stomach of birds or carnivores.
Ameghino puts most of the forms in the family Cephalomidae, which he considers ancestral to Hystricomorpha in general. I feel, however, that it is better to assign the Deseado genera to the families which have persisted until recent times, as Scott and Ameghino, in another place, have done. There are six living families, four of which Scott found already represented in the Santa Cruz. Two of these clearly may be continued back into the Deseado, the Erethizontidae, and the Chinchillidae, nothing as yet having been found to represent the Santa Cruz families Cavidae and Octodontidae.