226 
nature of the food this powerful dental 
armature was intended to crush, and 
it is therefore idle to conjecture 
whether the creature was carnivorous 
or herbivorous, although, from the 
fact of its having been terrestrial, or 
partially aquatic, it is perhaps more 
probable that it was a vegetarian. 
The type ot dentition presented 
by the tuateras naturally leads on 
to that shown by another group of 
approximately contemporaneous crea- 
tures, which may be called bean- 
toothed reptiles, although it by no 
means follows that the two groups 
are In any way nearly related, despite 
the fact that they are both character- 
ised by the short, broad, and triangular 
skull. The bean-toothed reptiles take 
Animal Life 
Fig. 13. Side View of Dentition of a Carnivorous Mammatllike Reptile. 
their name from the presence of a small number of large flattened teeth covering 
nearly the whole of the palate, but replaced in the fore part of the jaws by teeth 
if] 
curious 
Vig. 14. Palatal View of Upper 
Dentition of Vritylodon. 
of a more ordinary type. 
are squared; but in a second (Cyamodus), as shown im Fig. 12, 
they are more rounded, and present a striking resemblance to 
those large flat, brown Australian beans so frequently used as 
pocket match-boxes. 
this type were used for crushing either the shells of molluses or 
>, the hard external coats of crabs and such-like creatures. 
The bean-toothed reptiles are near relatives of certain other 
extinct groups which claim special attention on account of the 
resemblance 
parts of the skeleton) to that of mammals. 
In one kind (Placodus) the palatal teeth 
There can be little doubt that teeth of 
dentition (as well as 
In this case the 
presented by their 
resemblance is not an instance of parallelism in development, but 
appears to indicate an intimate family relationship between the 
two groups, the mammal-like reptiles, as they are called, having almost certainly been 
the actual ancestors of mammals. 
will be observed that the teeth 
upper tusk biting 
hinder molars, or cheek-teeth, 
any of these carnivorous 
this may have been the case. 
In the species 
of which the dentition is figured (Fig. 13), it 
are few in 
number, and differentiated into incisors, tusks, and 
molars after the mammalian fashion, with the 
behind the lower 
have, 
their crowns of a more éomplex type than those 
of the front teeth, and it is far from improbable 
that in some instances these teeth may have 
been inserted by two or more roots. 
one. 
mammal-like reptiles 
had a single definite replacement of baby teeth 
by those of the adult series is not yet definitely 
ascertained, although it is quite possible that 
The 
moreover, 
Whether 
Fig. 15. Dentition of Dicynodon. 
