April, 1921. 



The Canadian Field-Naturalist. 



65 



case floated al)Out before reachino' its 

 final restino-place. 



The third family of herbivorous dino- 

 saurs found in the deposits along (the 

 Red Deer river is the armored or plated 

 dinosaurs. They were low. heaw-boned. 

 quadrupedal, land animals with very 

 short massive limbs. The feet were short 

 and stubby and somewhat resembled the 

 feet of a ' rhinoceros. The ribs were so 

 constructed and articulated as to throw 

 them well out and give a broad back and 

 a large body cavity much the shape of a 

 huge barrel. The hips were as much as 

 five feet broad though tlie animal was not 

 more than six feet high. 



These dinosaurs were completely incased 

 in dermal armor or bony scutes in the skin. 

 In some genera the scutes were high-keeled, 

 thick and as much as a foot and a half in 

 length, Avliile in other genera they w^ere 

 more plate-like with only slightly elevated 

 keels. The larger scutes were arranged in 

 rows along the back and sides while on the 

 under parts were ossicles of irregular shape 

 which protected the animal much as the 

 cliain armor protected the warrior of the 

 middle ages. Between the large scutes 

 were smaller ones and in the smaller in- 

 tervening spaces were tiny ossicles similar 

 to those on the under parts. It is quite 

 evident that these creatures were so ef- 

 fe(itivel.y armored that they need have no 

 fear of their'enemies. The tail terminated 

 ill a bom* club, about the size of a water 

 pail, which was made uj) of a number of 

 modified dermal scutes thoroughly fused 

 together. The eyes were protected by a 

 l)oiiy lid, and in at least one genus (Pano- 

 plosaurus) even tlie mouth Avas protected 

 l)y a plate of b(tne in the cheek, which Mr. 

 Ijambe has called the dental plate. The 

 mem])ers of this family also possessed a 

 liorny beak. These animals were so well 

 protected that tliey did not need speed as 

 a means of escape and so l)ecame a heavy 

 sluggish animal in which the main develop- 

 ment was strength to carry the heavy load. 



The armored dinosaurs had an excep- 

 tionally small brain, the cavity being 

 smaller than a man's fist. The neural 

 canal was greatly expanded within the 

 sacrum, and Prof. Marsh thought that this 

 was the seat of that part of the brain whicli 

 controlled the action of the animal. 



There are at leat four genera of car- 

 nivorous dinosaurs represented in these 

 rocks, the largest of which is Gorgosaurus. 

 While Gorgosaurus attained a length of 

 thirty feet there was a contemporaneous 

 carnivore which was probably not more 

 than eight or ten feet long. Only frag- 

 ments of the latter have been found and 

 it has not been described. 



Gorgosaurus had a much lighter frame 

 than the herbivorous forms and the limb 

 bones were hollow. The bones show many 

 well-developed areas for the attachment of 

 muscles. No doubt Gorgosaurus was much 

 more active than the herbivorous forms, 

 but of course was too heavy to be agile. 

 The smaller forms were probably much 

 more active. 



The carnivorous forms walked on their 

 liind feet only, and used their huge tails 

 as balancing organs. The front limbs were 

 very small, specially in Gorgosaurus, and 

 could have been of little use. This limb 

 was becoming vestigial as shown by the 

 .study of earlier carnivorous dinosaurs. 

 The fore-limb possessed only two func- 

 tional digits and one metacarpal which 

 was vestigial, while the hind foot had 

 three Avell developed and powerful toes 

 and a smaller one at the back similar to 

 tlie back toe of a turkey. The fifth toe 

 was represented by the proximal part of 

 the metatarsal. The terminal phalanges 

 each bore a i)owerful claw. Gorgosaurus 

 luid four powerful jaws in w'hich were more 

 than sixty sharp, double-edged, recurved 

 teeth, some of which were four inches long. 

 It must have been a fierce looking lizard 

 as the name implies. 



Mr. L. M. Lambe suggested that Gorgo- 

 saurus may have been a scavenger, since 

 the teeth of the type specimen showed no 

 sign of wear. 



Another fairly well-known genus is Or- 

 nifliominus which was much smaller and of 

 more slender construction than Gorgosau- 

 rus. 



The carnivorous dinosaurs were not 

 fitted for life in the water. 



E.rtinction. It is impossible to saj' what 

 caused the etxermination of the dinosaurs, 

 ('hanging conditions with the cutting off 

 cf their food suoDly and their inability to 

 migrate great distances may have been one 

 cause. The rise of the mammals with their 



