33 
The dermal armour is of particular interest in comparing 
Anodontosaurus with certain genera which are founded primarily on 
dermal armour or portions of the skeleton other than the skull. In this 
class, among the American forms would fall Nodosaurus 1 Stegopelta?, 
H eirosaurus 3 , Hoplitosaurus 4 , etc. In all of these the dermal armour 
is so distinctly different from Anodontosaurus that they may be dismissed 
from further consideration. 
The distinguishing feature of the dermal scutes in Anodontosaurus is 
their extreme and uniform thinness ( See Plate XX). The scutes are of 
approximately the same thickness throughout, regardless of their size 
or shape, and even the long, high-keeled scutes are thin walled. These 
somewhat resemble a very steep-pitch roof with the upper part of the 
roof developed into a high, narrow ridge. The apex of these scutes 
is behind the midlength. They are asymmetrical, the narrow apex over- 
hanging, presumably, the external edge. The plates grade from these 
long, high, narrow ones (c), through moderately narrow, high-keeled (d), 
and oval, low-keeled (a and e ), to oval, flat plates (/). The exception 
to the rule of a uniformly thin wall is to be found in some small, circular 
plates with high, median points ( b ). In these the thickness through the 
apex is much greater than through other parts of the plate, but even 
here there is a decided concavity on the inferior surface. Plate XX shows 
cross-sections of the different types of plates preserved with the specimen. 
The sections are transverse through the apex of the plates and are natural 
size. 
The plates are made up of thin, dense bone. The external surface 
is covered with fine, vascular grooves and small pits. The inferior surface 
is somewhat rougher and lacks the vascular markings, and in most cases 
also the pitting. The largest plate preserved with the type is 235 mm. long, 
137 mm. high, and has an average wall thickness of 7 mm. (Plate XIX, c). 
There are three of these larger, steep-sided plates preserved. 
It is probable that with the loss of teeth Anodontosaurus changed its 
feeding habits and environment and did not need such heavy dermal 
armour. It might be possible that Anodontosaurus had developed a liking 
for invertebrate animals which were numerous in the Edmonton swamps 
and the decreased weight of the dermal armour would be less cumbersome 
in wading through the swamps. The extremely broad body, short, massive 
limbs, and splayed feet would enable the plated dinosaurs to progress 
through rather soft ground in spite of the heavy armour. 
1 Nodosaurus textilis Marsh, See Lull, Am. Jour. Sci., vol. I (Feb. 1921). 
* Stegopelta landerensis Williston, See Moodie, Kan. Univ. Sei. Bull., vol. 5, p. 257 (1911). 
* Heirosaurus sternbergi Wieland, Am. Jour. Sci., vol. XXVII, p. 250 (1909). 
* Hoplitosaurus marshi (Lucas), See Gilmore, Bull. U. S. N. M., p. 114 (1914), 
