324 



THE RISE OF ANIMAL LIFE 



You will observe by these remains 

 The creature had two sets of brains — 

 One in his head (the usual place), 

 The other at his spinal base. 

 Thus he could reason a priori 

 As well as o posteriori. 

 No problem bothered him a bit 

 He made both head and tail of it. 

 So wise was he, so wise and solemn. 

 Each thought filled just a spinal column. 

 If one brain found the pressure strong 

 It passed a few ideas along. 

 . If something slipped his forward mind 

 'Twas rescued by the one behind. 

 And if in error he was caught 

 He had a saving afterthought. 

 As he thought twice before he spoke 

 He had no judgment to revoke. 

 Thus he could think without congestion 

 Upon both sides of every question. 

 Oh, gaze upon this model beast. 

 Defunct ten million years at least. 



Horned dinosaurs such as Triceratops 

 were the last of the large dinosaurs (Fig. 

 13-41). The body was relatively bare but 

 the head was heavily armed with bony or- 

 gans of defense. Two great horns protruded 

 anteriorly over the eyes and another over 

 the ridge of the nose. An enormous flare 

 of bone extended out from the back of the 

 neck which probably functioned admir- 

 ably in preventing an injurious blow to this 

 vulnerable region. 



It has been a question why these great 

 animals became extinct by the end of the 

 Cretaceous Period. There are many an- 

 swers, but possibly a combination of many 

 factors was responsible for their extinc- 

 tion. Since the flesh-eaters depended on the 

 plant feeders for food, a gradual extinction 

 of the latter meant annihilation of the 

 former as well. Geological changes going 

 on at that time indicate that the land was 

 gradually rising, culminating in tlie forma- 

 tion of the Rocky Mountains in this country. 

 This meant not only less water and conse- 

 quently fewer swamps where these animals 

 lived, but also cooler climates and perhaps 

 much less vegetation. With the declining 

 food supply the great herbivores starved to 

 death, taking the carnivores with them. 



Thus ended the reign of the greatest group 

 of animals that have ever lived on the earth 

 thus far. The future may brings others but 

 it seems highly unlikely that they will reach 

 such size as these mighty beasts. 



Modern reptiles 



From tlie time of Seymoiiria certain rep- 

 tiles have continued down to the present 

 time. In some regions they are rather nu- 

 merous, but in comparison to their glorious 

 past they are mere remnants. At least six- 

 teen orders of reptiles have lived on the 

 earth; today only four remain (Fig. 13-41). 

 Of these, one is nearly extinct but it does 

 include a species, Sphenodon, more com- 

 monly known as Tuatara (Fig. 13-43), 

 which is of considerable interest because it 

 carries in its body many anatomical fea- 

 tures definitely identifying it with the 

 earliest of reptiles. Tuatara has appropri- 

 ately been called a "living fossil." Many of 

 its characteristics show a definite relation- 

 ship to the stem reptiles as well as to mod- 

 ern reptiles. It is always interesting to 

 speculate why such isolated members of a 

 once flourishing group were able to survive 

 down to the present day when all its rela- 

 tives are long since extinct. In the case of 

 Tuatara, its location is probably responsi- 

 ble; the reptile lives in New Zealand where 

 it has had few, if any, natural enemies. 

 Tuatara living in other parts of the world 

 were set upon and apparently destroyed by 

 the aggressive, more agile mammals. Thus 

 it can be said that isolation has saved one 

 species of animal. Since its environment has 

 remained unchanged, Tuatara, itself, has 

 changed but little through the past 200 

 million years. 



The surviving members of the great rul- 

 ing reptiles, the dinosaurs, are the croco- 

 diles, the caimans of the Amazon, the 

 gavials of the Ganges and the alligators of 

 today (Fig. 13-44). Although feeble in size 

 and small in numbers compared to the 

 dinosaurs, some do reach a length of 30 

 feet. They inhabit the large rivers of the 



