MESOZOIC ERA: THE AGE OF REPTILES 551 



"Now, as long as food is abundant, the larger individuals of a race have the better 

 chances, both to repulse or escape enemies, and to drive off rivals of their own kind. 

 Therefore, the tendency is for a race to increase steadily in size so long as food is abun- 

 dant, up to a maximum above indicated. But if a scarcity of food ensues, the larger 

 animals may all be suddenly swept out of existence, and if the smaller ones have been 

 eliminated through the gradual evolution of the race during the period of plenty, the 

 whole race may become extinct, or be driven to other regions, where if it is unable to 

 adapt itself successfully to its new environment, it will finally disappear. 



"For these reasons, it seems probable that we should regard all large animals as, 

 so to speak, on the verge of extinction. They may not cross the verge for a long time, 

 but they are always easily pushed across by some unfavorable climatic or environ- 

 mental changes." (Manuscript of W. D. Matthew.) 



REFERENCES FOR DINOSAURS 



General 



Deferet, Chas., — Transformations of the Animal World. 



Hutchinson, H. N., — Extinct Monsters and Creatures of Other Days, pp. 124-186. 



Jaekel, 0., — Die Wirbeltiere. 



Lankester, E. R., — Extinct Animals, pp. 199-202. 



Lucas, F. A., — Animals of the Past, pp. 90-110. 



Lucas, F. A., — Animals before Man in North America, pp. 143-172. 



Lull, R. S., — Dinosaurian Distribution : Am. Jour. Sci., Vol. 29, 1910, pp. 1—39. 



Lull, R. S., — Nature's Hieroglyphics : Pop. Sci. Monthly, Vol. 66, 1904, pp. 139-149. 



Marsh, O. C, — Dinosaurs of North America: Sixteenth Ann. Rept., U. S. Geol. 



Surv., 1896, pp. I43-244- 

 Von Reichenbach, E. F. S., — Lehrbuch der Palaozoologie, Vol. 2. 

 Woodward, A. S., — Vertebrate Paleontology. 

 Zittel-Eastman, — Textbook of Paleontology. 



Carnivorous Dinosaurs (Theropoda) 



Matthew, W. D., — Allosaurus, a Carnivorous Dinosaur, and its Prey: Am. Museum 



Jour., Vol. 8, 1908, pp. 3-5. 

 The Tyrannosaurus : Am. Museum Jour., Vol. 10, 1910, pp. 1-8. 



Unarmored Quadruped Dinosaurs (Sauropoda) 



African Dinosaurs, a Review: Geog. Jour., Vol. 42, 1913, p. 389. 



Matthew, W. D., — The Mounted Skeleton of Brontosaurus: Am. Museum Jour., 



Vol. 5, 1905, pp. 63-70. 

 Wieland, G. R., — Dinosaurian Gastroliths: Science, Vol. 23, 1906, pp. 819-821. 



Bipedal Herbivorous Dinosaurs (Unarmored Predentata) 



Brown, B., — The Trachodon Group: Am. Museum Jour., Vol. 8, 1908, pp. 51-56. 

 Hutchinson, H. N., — Extinct Monsters and Creatures of Other Days, pp. 158-171. 

 Osborn, H. F., — A Dinosaur Mummy: Am. Museum Jour., Vol. 11, 191 1, pp. 7-1 1. 



