SINCLAIR : TYPOTHERIA OF THE SANTA CRUZ BEDS. 
7 
RELATIONSHIPS OF THE SANTA CRUZ TYPOTHERIA. 
I. With the Toxodonta. 
The Santa Cruz Typotheria represent a stage in the evolution of certain 
structures which is less advanced than that displayed by the contemporary 
Nesodons. This is especially true of the feet and teeth. 
The feet of Nesodon (text figs. 3, B ; 4, B) are tridactyl, with the axis 
passing through the third digit. The manus has been derived from a 
Fig. 3. 
A, Protypotherium australc, left fore foot, x | (No. 9149 American Museum) ; B, Nesodon 
imbricatus , left fore foot, about x \ (No. 15,460). 
tetradactyl foot like that of Protypotherium (text fig. 3, A ; PI. V, fig. 3) 
or Pachyrukhos (PI. X, fig. 14) by the loss of the fifth digit, a vestigial 
metacarpal V still remaining. The mutual relationships of the carpal and 
metacarpal elements are similar in both. 
The three-toed pes of Nesodon (text fig. 4, B) is the outcome of a stage 
of digital reduction already well advanced in Hegetotherhim (text fig. 4, A ; 
PI. II, fig. 19), attained by the complete loss of digit V and the fusion of 
the ento- and mesocuneiforms. The naviculo-calcaneal contact, overlap of 
metatarsal II on the ectocuneiform and the strongly interlocking proximal 
articulations between the third and fourth metatarsals (see Pis. II, fig. 18; 
V, fig. 2) are present in Nesodon as in Hegetotherium. In Nesodon the 
shortening of the neck of the astragalus and the increase in size of the 
fibular facet on the calcaneum are, perhaps, adaptations to the support of 
weight. 
