108 EXTINCT MONSTERS 
Some of the arguments used by Owen in his Memoir, above 
referred to, may be briefly condensed as follows: The creatures 
to which these skulls belonged were not mammals (although to 
an evolutionist they are a foreshadowing of that class), both on 
account of the double nasal apertures, one of which is seen in 
Fig. 26; and also because no mammal has a brain-cavity so 
relatively small. They were not crocodiles, as indicated by 
certain other features of the skull. They were not turtles or 
Fic. 26.—Anomodont skulls. A, skull of Dicynodon; B, skull of Owdenodon, 
from Karoo strata, South Africa. (After Owen.) 
tortoises, for all such reptiles have a single nasal opening placed 
in the middle of the fore part of the skull. They could not be 
fishes, for fishes breathe in quite a different way. Neither could 
they be batrachians (frogs, etc.), nor yet snakes, as is also proved 
by the structure of their skulls. Certain other features of the 
skull show a relationship with the Lacertilians, or true lizards. 
The skulls are mostly of small size; but that of Dicynodon 
tigriceps is as much as twenty inches in length. That of 
