Lydekker made an order Astrapotheria including the Astrapotheria and Homalodontotheria, but as the dentition of the two groups is so different, because of the enormous enlargement of the frontal region, and because of the reduction of the premolars, I am convinced that these two groups represent totally divergent lines of development; and I have therefore made each of the groups a separate suborder.
Ameghino has described several genera, which make a progressive series and show a constantly progressive variation as far as they are known.
| Genus | Formation | Formula | |
|---|---|---|---|
| Albertogaudryi | Casamayor | ? 1 ? 3 | Post, inner and post |
| ? 1 ? 3 | isolated. median. | ||
| cusps isolated. | |||
| Astraponotus | Astraponotus | ? 1 2 3 | Post. inner cusp, |
| ? 1 ? 3 | united with wall | ||
| making small lobe. | |||
| Parastrapotherium | Deseado and Colpodon | ? 1 2 3 | Post. lobe large, also |
| 3 1 2 3 | also a strong crista. | ||
| Astrapothericulus | Astrapothericulus | ? 1 2 3 | |
| 3 1 2 3 | |||
| Astrapotherium | Santa Cruz | 3 1 2 3 | |
| 3 1 1 3 |
In the Deseado beds, beside Parastropotherium, Ameghino has described Liarthrus, based on an upper second premolar and part of another tooth, but I can see no structural variation from Parastropotherium or indeed from P. holmbergi; so I consider this genus as a synonym. As to the genus Traspoatherium, I can not see in it any reason for making a genus separate from Parastrapotherium.
Parastrapotherium Ameghino
- Parastrapotherium Amegh., 1895, Bol. Inst. Geog. Argen., t. 15, p. 636.
- Parastrapotherium Amegh., 1897, Bol. Inst. Geog. Argen., t. 18, p. 449.
- Liarthrus Amegh., 1895, Bol. Inst. Geog. Argen., t. 15, p. 641.
- Liarthrus Amegh., 1897, Bol. Inst. Geog. Argen., t. 18, p. 451.
- Traspoatherium Amegh., 1895, Bol. Inst. Geog. Argen., t. 15, p. 641.
- Traspoatherium Amegh., 1897, Bol. Inst. Geog. Argen., t. 18, p. 450.
The genus, in general, is similar to Astrapotherium, so that Gaudry considered it the same, but Ameghino has distinguished it by the tushes being relatively of smaller size, the lower incisors larger, and by the presence of pm. 3 in the lower series. The Deseado forms are also of considerably larger size than the Santa Cruz.
Our material includes a pair of lower jaws, two scapulae, the humerus, and the lower end of the femur.
No skull has been found in the Deseado. Those from the Santa Cruz are enormously swollen over the orbits, the massive bone making a skull wholly unique. The lower jaws are similar to those of Astrapotherium, except that the rami are deeper. The front ends are fused and expanded making the anterior much enlarged, and causing the incisors to stand at intervals as in Coryphodon. The symphysis is massive and prolonged backward nearly to premolar 3. The rami are plump and unusually thick.
