Based on an imperfect mandibular symphysis, in which incisor 3 is very large.
CHAPTER VIII
Nesodontidae
This family is characterized by the teeth being hypsodont, the second upper incisor and the third lower incisor being enlarged into caniniform teeth, the upper molars complicated by the development of cristae, limbs short, feet tridactyl and semidigitigrade.
Fig. 79. A, upper and a lower molars 2 of Proadinotherium;
B, upper and b lower molars 2 of Coresodon;
C upper and c lower molars 2 of Neudon—
½ natural size.
In the Santa Cruz, the family is represented by the two genera Nesodon and Adinotherium. In the Deseado we find Proadinotherium evidently ancestral to Adinotherium and very little differentiated from it. Ameghino has described a genus, Pronesodon, which is evidently ancestral to Nesodon. I have referred Coresodon to this family because the molars of the upper and lower jaws are very close to those of Adinotherium. Ameghino has also described two genera, Nesohippus and Interhippus, based on upper molars which are very similar in pattern to Adinotherium and which I believe belong to this family, if they prove to be valid genera, of which I have some doubt, feeling that they will prove to be the deciduous upper premolars of Proadinotherium or some similar form. The genus Senodon, which Ameghino also places in this family, I feel will prove to be worn teeth of Leontinia.
Proadinotherium Ameghino
Proadinotherium Amegh., 1895, Bol. Inst. Geog. Argen., t. 15, p. 625.