Fig. 40. Restoration of Prosotherium garzoni—
⅓ natural size. (Half tone.)
Prosotherium triangulidens Ameghino
P. triangulidens Amegh., 1897, Bol. Inst. Geog. Argen., t. 18, p. 427.
P. robustum, Amegh., 1897, Bol. Inst. Geog. Argen., t. 18, p. 427.
P. quartum Amegh., 1901, Bol. Acad. Nac. Cienc. Cordoba, t. 16, p. 371.
This species is similar to P. garzoni except for size, the forms running about 12% larger, and being heavier built. In this same line the upper and lower molars are relatively wider and heavier. The top of the skull also is wider. I have drawn carefully the skull and dentition so that the detail can be seen from the figures. Beside triangulidens, Ameghino described P. robustum, which, as far as I can see, differs only in being about 5% larger, which is well within individual variation, so I have considered it as a synonym. The same is the case with P. quartum, which Ameghino distinguishes as being about the size of P. robustum, and having lower pm. 1 present. The latter character we found also characteristic of P. garzoni, so only size remains and I do not consider less than 10% enough by itself to make a species.
| Measurements | |
|---|---|
| Skull, length | 110 mm. |
| Upper dentition, length inc. 1 to m. 3 | 57 mm. |
| Upper dentition, length pm. 1 to m. 3 | 35 mm. |
| Upper dentition, incisor 1, width | 8 mm. |
| Upper dentition, molar 1, width | 4½ mm. |
| Six specimens from Chico del Chubut | |
Propachyrucos Ameghino
Propachyrucos Amegh., 1897, Bol. Inst. Geog. Argen., t. 18, p. 425.
The genus is based on lower jaws, in which the characters of the premolars, the molars and the first two incisors, resemble those of Pachyrukhos; but in this genus the third incisor, the canine, and the first premolar are retained and but little reduced. Ameghino has described two species, P. smithwoodwardi, and P. aequilatus.