CHAPTER VI 
‘TOXODONTIA 
THE toxodonts of the Deseado are much more varied 
than those of the Santa Cruz, and less so than those of 
the Casamayor; the teeth less hypsodont than in the Santa 
Cruz, and more hypsodont than in the Casamayor; are 
smaller than those of the Santa Cruz, and larger than those 
from the Casamayor. It isa group of heavy, short-limbed, 
nonadaptive animals, which, as time and competition pro- 
gressed, gradually diminished in numbers and variety. 
The ancestral type must be sought in some such a form 
as Henricosbornia, where the upper molars are brachydont, 
have the four primary cusps distinct, and the connecting 
crests of small size, and a cingulum moderately developed 
on the front and rear sides. Progress is in the line of en- 
larging the crests, so that, in the later forms, the two exter- 
nal cusps are united to make a wall; and the anterior 
external and the anterior internal cusps are united into the 
large anterior lobe; while the posterior external and the 
posterior internal cusps unite to make the posterior lobe. 
These may remain relatively simple as in Rhynchippidae* ; 
or with this simple arrangement of the cusps, the cingulum 
may be developed into a platform around the anterior, 
inner, and posterior sides of the molars, as in the [sotem- 
nidae; or, with relatively simple molars, the incisors may 
be specialized into caniniform-like teeth as in the Leon- 
tiniidae; or secondary processes (or cristae) may develop 
from the wall, making the complicated teeth characteristic 
of Nesodontidae. 
+ | have abandoned the family term Nolohippidae, as the genus used as a 
basis is very little known, and the forms Ameghino assigns to the family, to 
my mind, mostly belong with the Nesodontidae. 
