Cope.] 80 [Feb. 17, 
On the Mechanical Origin of the Dentition of the Amblypoda. 
By E. D. Cope. 
(Read before the American Philosophical Society, February 17th, 1888.) 
As the Amblypoda form the only order of ungulate Mammalia with tri- 
tubercular superior and tuberculo-sectorial inferior molars, the ques- 
tion has arisen in my mind why they did not develop a sectorial den- 
tition in the same way, and for the same mechanical reasons, that the un- 
guiculate series has done sv. Having recently assigned* certain mechani- 
cal reasons for the evolution of the sectorial teeth of the Carnivora, it is 
necessary to explain why the Amblypoda, which had apparently the same 
mechanical conditions at the start, did not eventually produce the same 
result. 
In the first place I observe in the families Coryphodontide and Uinta- 
theriide of the Amblypoda, that the shearing the inferior molar crests 
against the superior molar crests, is from before backwards. In the Cre- 
odonta and Carnivora it is from behind forwards. I supposed the latter 
movement to be due in these animals to the wedging of the inferior canine 
in front of the superior canine, a movement undoubtedly sufficient to 
account for such a shearing, other things being equal. But in the Coryph- 
odontide the canines are greatly developed, yet the shearing of the molar 
crests is in the opposite direction. It is also evident that the development 
of the canines cannot have been the cause of the maintenance of any kind of 
a shear between alternating parts of molar teeth, otherwise the quadrituber- 
cular type of molar would not have come into existence in such families 
as have large canine teeth, such as the Suoid Artiodactyla. I do not for 
these reasons abandon the opinion that the development of the canines has 
not had a great deal to do with the development of the sectorial dentition. 
LT only deny that it has been the cause of its origin, that is, of the anterior 
shearing of the lower molars on the upper, at its beginning. 
The divergence of mammalian dentition into the two types, the tritu- 
bercular and quadritubercular, has been, as it appears to me, due to the 
adoption of different food-habits. The tritubercular is the primitive, and 
is adapted for softer food, as flesh, so that primitive placental Mammalia 
were carnivorous or nearly so, The mastication of hard food was impos- 
sible until the molars of the two series opposed each other, and this was 
not accomplished until the quadritubercular superior molar was produced. 
This was accomplished, as I have pointed out, by the addition of a poste- 
rior internal tubercle, and I suspect that the mechanical cause of its origin 
was the attempt of the animal in mastication to crush substances harder 
than flesh against this posterior edge of the superior molar, by applying 
to it the anterior edge of the lower molar. In the devouring of flesh this 
movement is not necessary or only necessary so far as to produce a shear- 
*The Mechanical Origin of the Sectorial Teeth of the Carnivora. Proceeds. Amer, 
Assoc. Ady. Sci, 1887, p. 254. 
