58 ORIGIN OF TOOTH PATTERNS CHAP. 
“talon”; and this ledge became produced into two additional 
cusps, the hypoconule or hypoconulid, and the ectocone or ecto- 
conid. Thus the typical sextuberculate tooth of the primitive 
Uneulate, and indeed of many primitive Eutherians, is arrived at. 
protoconid. 
\ metaconid 
me y 
Ptraconid ~ 
Fic. 39.—Epitome of the evolution of a cusped tooth. 1, Reptile ; 2, Dromatherium ; 
3, Microconodon ; 4, Spalacotherium : ime, metaconid ; pa, paraconid ; pr, proto- 
conid ; 5, Amphitherium. (After Osborn. ) 
From this the still further complicated teeth of modern Ungulates 
can be derived by further additions or fusions, etc.’ On the other 
hand, the development of the Primate molar stops short at the 
stage of four cusps. 
That such a series can be traced is an undoubted fact. Every 
stage exists, or has existed. But whether the stages can be con- 
nected or not is quite another question. It is by three main 
lines of argument that the view here sketched out in brief is 
supported. In the first place, the tracing of the pedigrees of 
many groups of mammals has met with very considerable success ; 
and it is clear that as we pass from the living Horse and 
Rhinoceros, with their complicated molars, to their forerunners, 
we find that both can be referred to a primitive Ungulate molar 
with but six cusps. Going still further back to the lowest 
Kocene and ancestral type as it appears, Huprotogonia, we still 
find in the molar tooth the sextubercular plan of structure. We 
can hardly get further back in the evolution of the Perissodactyles 
with any probability of security. On the other hand, many facts 
point toa fundamental relationship between the primitive Ungu- 
lates and the early Creodonts. The latter frequently show plainly 
tritubercular molars. Such Ungulates as Luprotogonia and Proto- 
ygonodon, though sex- or quinque-tubercular as to their molars, 
have a distinctly prevailing trituberculism, when the size and 
importance of three of the cusps is taken into account. But this 
' e.g. the ‘‘ protoloph,” ‘‘metaloph,” etc. (see Fig. 36, p. 51), of the modern 
Ungulate form of tooth. 
a 
