MAMMALIA OF THE SANTA CRUZ BEDS 
PART II. T0X0D0NTA. 
BY 
WILLIAM B. SCOTT, 
Princeton University. 
T HE known representatives of this suborder range from rather small 
to very large and massive animals, always much exceeding in 
bulk and stature the contemporary Typotheria, but, in Santa Cruz 
times, equalled or even surpassed by the Entelonychia, not to mention 
the Astrapotheria, some species of which are the largest mammals known 
from the Santa Cruz beds. 
In this group the dental formula is very generally unreduced : If Cf, 
Pf, Mf, though there is some individual variability in the number of small 
and functionally unimportant teeth between the incisor tusks (i- and 3) and 
the cheek-teeth. Only in Phobereotherium is there a significant difference 
from the usual formula in the absence of the upper median incisors. A 
highly characteristic feature of the suborder is the arrangement of the 
incisors and the remarkable changes in appearance and relative size which 
these teeth undergo during the lifetime of the individual animal. The 
second upper and third lower incisors (i- and ?) are much enlarged and 
grow throughout life, or, at least, to very advanced age, and form moder- 
ately large tusks, such as are found in no other subdivision of the order. 
Indeed, this arrangement occurs in no other known group of Santa Cruz 
ungulates except in the family Proterotheriidae of the Litopterna (see Vol. 
VII, p. 8) in which, however, these tusks are relatively small. The very 
large tusks, of the Astrapotheria are canines. The teeth, especially the 
tusks and the true molars, display a strong tendency to hypsodontism, 
the former growing from persistent pulps and the latter forming their 
roots at an advanced stage of wear. The crowns are incompletely covered 
