THE ANIMAL CLIMAX-THE CHORDATES 



323 



Many of the dinosaurs developed the 

 bipedal method of locomotion, that is, they 

 rose on their hind legs when in haste and 

 propelled themselves entirely by these two 

 appendages. This idea proved successful in 

 some of the largest flesh-eaters, which had 

 powerful hind legs but only short anterior 

 appendages (Fig. 13-41). Bipedal locomo- 

 tion in four-footed animals is, then, very 

 ancient. 



Footprints left in various parts of the 

 world by these ancient animals have given 

 paleontologists some interesting evidence 

 as to the nature of the reptiles that made 

 them (Fig. 13-42). For example, in the 

 old mud flats of the Connecticut Valley 

 there are those that resemble bird foot- 

 prints of today, and hence were first 

 thought to be those of giant birds. One in- 

 teresting small dinosaur was the "ostrich 

 dinosaur," which was toothless and pos- 

 sessed a hornlike bill resembling that of a 

 bird. It had long hind legs, indicating its 

 great ability to run. Scientists have debated 

 its possible habits; one suggestion made is 

 that the animal probably fed upon the eggs 

 of other dinosaurs. With such a diet, it 

 would be understandable why the animal 

 had no teeth. Long legs would be its means 

 of escape once it was detected by the owner 

 of the eggs. One report, according to 

 Romer, states that a crushed skull of the 

 ostrich dinosaur was found near the nest- 

 ing grounds of the horned dinosaurs; if the 

 complete story were known, it might be a 

 case where the owners caught the thief 

 practicing his trade. 



The flesh-eaters grew to enormous size 

 and the largest one unearthed, Tyranno- 

 saiirus ( tyrant reptfle ) , reached a height of 

 19 feet (Fig. 13-41). It must have been 

 an awesome creature in those prehistoric 

 times, perhaps feared by all living crea- 

 tures. Its skull was over 4 feet in length and 

 the jaws were armed with a formidable set 

 of teeth, which must have functioned well 

 in rending and tearing other animals to bits. 

 It possessed massive hind legs and small 



front ones. It is thought that its chief source 

 of food was the giant amphibian forms 

 which existed at the same time. 



The great amphibious dinosaurs were 

 vegetarians and grew to great lengths and 

 heights but did not become as massive as 

 the flesh-eaters. Brontosanrus and Diplo- 

 dociis grew to the largest size and are the 

 ones most commonly displayed in museums. 

 They reached a length of 85 feet and a 

 weight of 40 tons or more. They walked 

 on all four feet and could look over a three- 

 story building. Their powerful legs were 

 placed in such a position as to carry their 

 body evenly balanced. The neck and tafl 

 were very long, in fact, they seem to bal- 

 ance one another on opposite ends of the 

 trunk. The head was much too small for 

 the size of the animal, and it is difficult to 

 see how it could house a brain sufficiently 

 large to govern such a massive hulk. 

 Furthermore, the jaws were so small and 

 weak that the animal must have been 

 forced to eat continuously to maintain itself. 

 The dorsally-placed nostrils have led sci- 

 entists to conclude that the animal was 

 amphibious and probably remained sub- 

 merged most of the time with only the 

 nostrils protruding above the surface of 

 the water for breathing air. The tremendous 

 burden would thus be partially buoyed up, 

 relieving the legs from bearing the entire 

 weight. 



In the hip region, the spinal column 

 supported an enlargement several times the 

 size of the brain. Apparently impulses re- 

 ceived by the brain from the sense organs 

 were sent down to the large posterior 

 ganglion which operated the posterior legs 

 and perhaps the rear portion of the body. 

 The strange anatomy of this great beast 

 inspired the late Bert L. Taylor of the 

 Chicago Tribune to write the following 

 poem : 



Behold the mighty dinosaur. 

 Famous in prehistoric lore. 

 Not only for his power and strength 

 But for his intellectual length. 



