64 



The Canadlan Field-Naturalist, 



Vol. XXXV. 



t(» the bill of a duck, hence the name 

 'Miick-billecV. 



The.'^e dinosaurs were purely herbivor- 

 ous as sliowu by their teeth. The teeth 

 were arrang-ed in a magazine in vertical 

 as well as horizontal rows. 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 were 

 five or more teet/i in each vertical row. 

 As the teeth became worn they were 

 pushed out and replaced by new ones 

 which were ever forming at the base of 

 tJhe magazine. In this respect they differ 

 from the mammals which have only two 

 sets of teet;i. The cutting surface of the 

 teeth was on the inside in the case of 

 the upper jaw and on the outside in 

 the lower jaw. The lower jaws passed 

 witihin the upper jaws and the teeth 

 worked like a pair of shears in cutting 

 the soft vegetation after it had |>een 

 nipped off wit^i 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 eadh hind foot. In gen- 

 eral build of the limbs a ad feet they 

 somewhat resembled the rjiinov'eros. 



These animals had the largest heads of 

 any land animal known. In the case 

 of one {Chasmosaurus helli Lambe) the 

 skull covered half the lengtlh from the 

 snout to the drop of t/ie tail, measuring 

 five and one half feet. Triceratiops skulls, 

 (from a more recent formation) have 

 been recorded up to nine feet in length. 

 These huge skulls were solidly consti-ucted 

 and were sunnounted ])y three bonis one 

 over each eye and one over the nose. 



In some eases the nasal horn was greatly 

 developed at the expense of the supra- 

 orbital horns, while in otiher genera the 

 revenue was true. The back of the skull 

 was developed into a large crest or shield 

 which extended over the neck and shoul- 

 ders. T/iis crest Jielped to give the skull 

 its huge proportions and with the horns 

 must have been a formidable means of 

 df'fence. The snout was developed into 

 a wharp cutting beak incased in a horny 



sheath, similar to that of a ])arrot but 

 many times as large. This beak was 

 probably used for cutlting off tlie vege- 

 tation on whic^i the animal fed. The 

 horned dinosaui's 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, but 

 fewer in number. They show tihat the 

 animal was herbivorous in habit. The 

 tail w^as shorter and more uearly round 

 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-imbricating poly- 

 gonal scales which 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 brougftit to light 

 was tjtiat described by the late Mr. L. M. 

 Lambe in the Ottawa Naturalist for Jan- 

 uary, 1914. 



It is probable that these animals were 

 gregarious in habit, ais 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 tihey assembled in certain swam- 

 py or low-lying areas 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 they lived and 

 died out of the Avater, and as the skull, 

 whidh was solidly constructed, was more 

 durable than the resti of the skeleton, it 

 may have lain on the banks for months 

 before it wais ]iicked 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 tjie case of the water-inhabitating 

 duck-billed creatures whovse skulls were 

 more fragile and seem to have l>een eaisily 

 ddached from the body and d<'sti\)yed. 

 In tlif Belly River fonnation it is com- 

 mon to find skeletons of the duck-billed 

 dinf)saurs without the head. This seems 

 to prove that the neck was weak and 

 allowed the head to drop off as t/ie ear- 



