This order of South American ungulates is less abundantly represented in the Deseado formation than in the Santa Cruz, but most of the genera of this latter formation have representatives in the Deseado so that they seem to have diverged still earlier.
By Scott the order is divided into two families, the Proterotheriidae and the Macrauchenidae, the less known Adiantidae being placed under the latter family until better known. I feel that I should prefer to retain the Adiantidae for the present, until they can be shown to be subordinate to another family, so that in this paper the three families are retained. The striking features of the two larger families may be best brought out by a comparison of their chief features as follows.
| Proterotheriidae | Macrauchenidae | |
|---|---|---|
| Formula | 1 0 4 3 | 3 1 4 3 |
| 2 0 4 3 | 3 1 4 3 | |
| Upper inc. 2 and lower inc. | Incisors, canine, and premolar | |
| 3 enlarged and tush-like, | 1 simple, compressed, subequal | |
| growing from persistent pulps. | in size, and rooted. | |
| Nasals normal. | Nasals shortened indicating | |
| a proboscis. | ||
| Neck short. | Neck long. | |
| Feet with median digit enlarged, | Feet with all three digits | |
| lateral digits reduced. | subequal in size. | |
Proterotheriidae Ameghino
In the Deseado, this family is scantily represented as compared with the rich fauna, both as to species and numbers of individuals in the Santa Cruz, but of the four chief genera of the Santa Cruz, three have been found, though the remains are very fragmentary. They are the genera Eoprototherium, belonging to the Prototherium series, Deuterotherium belonging to the Thaotheriumseries, and Notodiaphorus representing the Diadiaphorus series.
The following table will give what is known in comparing the two series.
| Period | Upper Molars | Nasals | Pes | |
|---|---|---|---|---|
| Proterotherium | Santa Cruz | metaconule present protoconule and protocone separate | normal | tridactyl |
| Eoproterotherium | Deseado | metaconule present protoconule and protocone separate | ||
| Licaphrium | Santa Cruz | metaconule present | normal | tridactyl |
| Diadiaphorus | Santa Cruz | metaconule present protoconule and protocone fused | short | tridactyl |
| Notodiaphorus | Deseado | tridactyl | ||
| Thaotherium | Santa Cruz | metaconule lacking protoconule and protocone separate | normal | monodactyl |
| Deuterotherium | Deseado | metaconule lacking otoconule and protocone separate |
Eoproterotherium Ameghino
Eoproterotherium Amegh., 1904, Anal. Mus. Nac. B. A., ser. 3, t. 3, p. 441.
The genus is founded on single teeth of the upper molar series, which, except for size, are very like those of Proterotherium. Limbs, etc., are unknown, so that this genus is simply a carrying back of the Proterotherium line into the Deseado. We found no teeth of this form, but one species has been described, E. inaequifacies, of which I reproduce [Ameghino’s figure] compared with Proterotherium, which shows this species to have the metaconule better developed.