From the foregoing chart and the comparative figures of the upper and lower dentitions, the variety and at the same time the homogeneity of the _Typotheria_ is evident. The gnawing front teeth resemble those of rodents, especially in the genera where the enamel is lacking on all but the front face, but this is entirely a parallelism and there is no evident phylogenetic relationship. As to affinities with the _Hyracoidea_, Sinclair[12] has carefully balanced them and finds so little in common between the two groups that he makes them a separate suborder. I find certain features in common, like the lophiodont dentition with the tendency toward hypsodont incisors, the inflation of the tympanic and the extension of this up into the periotic region, and the general arrangement of the basicranial foramena. On the other hand, there are also numerous features in common with the Toxodonts, and several peculiar to the group, so that I would feel that all the Notungulates are descended from the _Hyracoidea_, and this group has developed its peculiarities in South America, retaining however a little more of the hyracoid aspect. [Footnote 12: Princeton Expeditions Reports, Vol. VI, p. 7, 1909.] [Illustration: Fig. 24. Comparative series of upper dentitions of Deseado and Santa Cruz Typotheria; _a_, Archaeohyrax patagonicus; _b_, Hegetotherium mirabile; _c_, Prosotherium garzoni; _d_, Pachrukhos moyani; _e_, Archaeophylus patrius; _f_, Interatherium extensum; _g_, Protypotherium australe; _h_, Argyrohyrax proavus; _i_, Eutrachytherus spegazzinianus—all natural size.] [Illustration: Fig. 25. Comparative series of lower dentitions of Deseado and Santa Cruz Typotheria; _a_, Archaeohyrax patagonicus; _b_, egetotherium mirabile; _c_, Prosotherium garzoni; _d_, Pachyrukhos moyani; _e_, Interatherium sp.; _f_, Protypotherium australe; _g_, Plagiarthrus clivus; _h_, Eutrachytherus spegazzinianus; _i_, Isoproedrium solitatium—all natural size.] The _Archaeohyracidae_ are the most primitive of the Deseado forms, but as all the families are already separated before this time the Deseado genera can not be considered as the ancestral ones, though they seem to have retained more of the primitive features.