322 



THE RISE OF ANIMAL LIFE 



Fig. 13-42. Dinosaurs often left footprints in soft mud that later became buried with fine sand, leaving almost per- 

 fect impressions of the feet of these ancient animals. The sedimentary rock in which this one was found sepa- 

 rated, so that both the mold (right) and the cast can be seen. 



discovery is a missing link, bearing resem- 

 blances to both amphibians and reptiles. It, 

 or forms like it, probably gave rise to the 

 great variety of reptiles known to have 

 lived during the Mesozoic Era and indeed, 

 to birds and mammals as well ( Fig. 13-41 ) . 

 The Age of Reptiles lasted over 100 million 

 years. By comparison it is estimated that 

 man is no older tlian a million years at 

 most. 



The dinosaurs 



The saga of the dinosaurs presents one of 



the most amazing stories ever told, a story 

 which has unfolded through a careful study 

 of fossil remains over a long period of time. 

 Dinosaurs had their meager beginnings in 

 the Triassic Period when they were small 

 unimportant animals. Evolving in both size 

 and numbers during the Jurassic and Cre- 

 taceous periods they reached the pinnacle 

 of walking land vertebrates near the close 

 of the Mesozoic Era, finally disappearing 

 from the earth never to appear again. They 

 ranged in size from the barnyard fowl to 

 the largest of all land animals. 



