726 GEOLOGY 



types are examples of analogous and parallel evolution, not of re- 

 lationship. 



The oldest known bird, Archceopteryx macrura (Fig. 497), shows 

 an advanced state of evolution, and at the same time clear traces 

 of reptilian ancestry. From this ancestry it retained a long, verte- 

 brated tail, reptile-like claws, fore limbs, teeth set in sockets, bicon- 

 cave vertebrae, and separate pelvic bones. On the other hand, 

 its head and brain were bird-like, its anterior limbs adapted to flying 

 in bird- (not pterosaurian) fashion, its posterior limbs modified for 

 bird-like walking, and most distinctive of all, it was clothed with 

 feathers. The development of the feathers, while yet the body 

 retained so many reptilian features, is most notable. But for their 

 fortunate preservation, it is uncertain whether the creature would 

 have been classed as a bird or reptile. The known specimen was 

 somewhat below the size of a crow. 



The marvelous deployment of aquatic and terrestrial reptiles 

 and of birds makes the scanty record of the mammals all the more 

 singular. Only a few jaw bones of the size of those of mice and r:it s 

 have been found. These low types are referred, without complete 

 certainty, to marsupials. They appear to have been insectivorous. 



The insects of the Jurassic appear to have included members of 

 nearly all the fossilizable groups that were not dependent on angio- 

 spermous plants. 



Map work. Folios published by the U. S. Geological Survey, good for the 

 study of the Jurassic and Triassic systems, are the following: California, 

 Downieville, Jackson, Pyramid Peak, Redding, San Luis; Colorado, Anthra- 

 cite-Crested Butte, Rico, Telluride, Tenmile, Walsenburg; Massachusetts- 

 Connecticut, Holyoke; Montana, Fort Benton; New Jersey, Passaic; New York- 

 New Jersey, New York City; Oregon, Roseburg; South Dakota-\<l>nix.(<t, 

 Oelrichs; Virginia-West Virginia- Maryland, Harpers Ferry; Wi/oniimj, \\- 

 ladin, Cloud Peak-Fort McKinney, Devils Tower. 



These folios may well be grouped geographically for study. Thus those 

 which deal with the Newark series of the east form one unit, those of tin- 

 Rocky Mountains another, those of the Pacific coast another. 



In the folios, the Jurassic and Triassic are commonly grouped together 

 under the name Jura-Trias, but the text of the folios often separates tin- 

 Jurassic from the Triassic, even where the map does not. 



