64 



The Canadian Field-Naturalist. 



A' 



XXXV 



to the bill of a duck, ihenee the name 

 '' duck-billed". 



These dijiosaurs were purely herbivor- 

 oxm as shown by their teeth. The teeth 

 were arranged in a magazine in vertical 

 as well as horizontal row^s. There were 

 more than twelve hundred teeth in the 

 four jaws but only about one in five of 

 these was in use at a time, as there w^ere 

 five or more teet,h in each vertical row. 

 As the teeth became worn they were 

 pushed out and replaced by new ones 

 which w^ere ever forming at the base of 

 the magazine. In this respect they differ 

 from the mammals which have only two 

 sets of teet^L The cutting surface of the 

 teeth was on the inside in the calse of 

 the upper jaw and on the outside in 

 the lower jaw. The lower jaws passed 

 within the upper jaws and the teeth 

 worked like a pair of shears in cutting 

 the soft vegetation after it had been 

 nipped off witjh the expanded beak. The 

 duck-billed dinosaurs ranged over much 

 of North America during late Cretaceous 

 times. 



The horned dinosaurs were quadru- 

 pedal land animals with short massive 

 limbs. There were five toes on each 

 front foot and four functional and one 

 vestigial toe on eadhi hind foot. In gen- 

 eral build of the lim.bs a ad feet they 

 somewhat resembled the rjvinoceros. 



These animals had the largest heads of 

 any land animal kiiovah In the case 

 of one {Chasmosaums 'belli Lambe) the 

 slmll covered half the lengtlh from the 

 snout to the drop of t^ie tail, measuring 

 five and one half feet. Triceratops skulls, 

 (from a more recent formation) have 

 been recorded up to nine feet in length. 

 These huge skulls were solidly constructed 

 and were surmounted by three horns one 

 over each eye and one over the nose. 



In some cases the nasal horn was greatly 

 developed at the expense of the supra- 

 orbital horns, while in other genera the 

 reverse was true. The back of the skull 

 was developed into a large crest or shield 

 which extended over tihe neck and shoul- 

 ders. T^his crest helped to give the skull 

 its huge proportions and with the horns 

 must have been a formidable meaas of 

 defence. The snout w^as developed into 

 a sharp cutting beak incaisied in a horny 



sheath, similar to that of a parrot but. 

 many times as large. This beak was 

 probably u'sed for cutiting off the vege- 

 tation on whic^i the animal fed._ The 

 horned dinosaurs had the distinction of 

 being the only reptiles which had double 

 rooted teettlh. The teeth were arranged 

 in magazines somewhat similar to the 

 teeth of the duck-billed dinosaurs, bul 

 few'er in number. They show liliat the 

 animal was herbivorous in habit. The 

 tail was shorter and more nearly roun<l 

 than in the before-mentioned family and 

 .sihows no adaptations for life in the 

 water. The skin of t^ie horned dinosaurs 

 was made up of non-imbrieatdng- poly- 

 gonal scales wdiieh were larger and some- 

 what thicker than those of the duck-billed 

 family. Some of the largest scales were 

 two inches in diameter. The first homed 

 dinosaur skin impression brougM to light 

 was t^iat described by the late Mr. L. M. 

 Lambe in the Ottawa Naturalist for Jan- 

 uary, 1914. 



It is probable that these aaiimals were 

 gregarious in habit, ajsi the writer has 

 obsei*ved a number of deposits of bones 

 in which only horned dinosaurs were re- 

 presented and seemingly only one genus 

 in each case. This would seem to indi- 

 cate that tlhey assembled in certain swam- 

 py or low-lying areasi from whic]i other 

 animals were excluded. 



Skulls of this family are much more 

 common than skeletons. This may be ex- 

 plained by the fact that tliey lived and 

 died out of the water, and as the skull. 

 w^hiclh, was solidly constructed, was more 

 durable than the resti of t^e skeleton, it 

 may have lain on the banks for months 

 before it was picked up by some flood 

 which carried it for miles. Thus the 

 skull would remain intact while the rest 

 of the skeleton woul be widely scattered. 

 The reverse of this situation is true 

 in t^ie case of the water-inhabitating 

 duck-billed creatures whose skulls were 

 more fragile and seem to have been eaisily 

 cletiached from the body and destroyed. 

 In the Belly River formation it is com- 

 mon to find skeletons of the duck-billed 

 dinosaurs without the head. This seems 

 to prove that the neck was weak and 

 allowed the head to drop off as tjie car- 



