AMPHIBIA AND REPTILIA OF COLORADO 45 



check. Some species may become harmful under artificial conditions, 

 when the balance of nature has been disturbed by the destruction of 

 their enemies, 1 but even under artificial conditions the checks upon 

 increase are usually sufficient to make them useful, rather than harm- 

 ful. Frogs are harmless and are used for food. Toads help to keep 

 insects in check about the house and garden. Lizards serve a similar 

 purpose in other places. Snakes subsist largely upon insects, mice 

 and other pests. Even the rattlesnake does much good in that way, 

 and, before the settlement of Colorado, served to keep the prairie- 

 dogs in check, congregating about the colonies of the latter during the 

 breeding season and subsisting on the young "dogs." On the other 

 hand, snakes do destroy some eggs and young birds of useful species, 

 though the harm they thus do is greatly outweighed by the good. 

 Except perhaps around poultry yards it would be better to destroy 

 only the rattlesnake. 



Extinct Reptilian Faunas. — The great amphibians of Carbonifer- 

 ous age do not seem to be represented in the rocks of Colorado, but 

 the gigantic lizard-like reptiles of Jurassic and Cretaceous times are 

 well represented, their fossil remains showing that some of them were 

 to be numbered among the largest, if not the largest, animals which 

 ever lived on the earth. These great lizards are often all referred 

 to as dinosaurs, although they include several distinct groups. Their 

 scattered bones occur in many parts of the state, but the most impor- 

 tant remains have been found near Canon City and Morrison. They 

 survived but a short while the retreat of the sea at the close of Creta- 

 ceous time, and are now wholly extinct everywhere. 2 During Ter- 

 tiary time large land tortoises lived in northeastern Colorado, and 

 their remains are found in the rocks of that age, especially in the 

 neighborhood of Pawnee Buttes. 3 



* Fisher, A. K., "The Economic Value of Predaceous Birds and Mammals," Yearbook of U.S. Dept. 

 Agric. for 1908, pp. 191-192, 1909. 



3 See Marsh, Othntel C., "Vertebrate Fossils," Geology of the Denver Basin in Colorado, U.S. Geol. 

 Sun., Monog., Vol. XXVII, pp. 473-527, 1886; "The Dinosaurs of North America," 16th Ann. Kept. U.S. 

 Geol. Sure., Part I, pp. 133-414, 1896; Hatcher, John B., "The Ceratopsia," U.S. Geol. Surv., Monog., Vol. 

 XLK, 1907; Case, E. C, "A Revision of the Cotylosauria of North America," Carnegie Inst. Wash., Pub. 

 No. 14s, 1911. 



J See Hay, Oliver P., "The Fossil Turtles of North America," Carnegie Inst. Wash., Pub. No. 75, 1908. 



