PHYLOGENY 



Figure 60. Photo- 

 graph OF THE ORIG- 

 INAL Archaeop- 

 TERYX Specimen. 

 Found in a quarry 

 of lithographic 

 stone at Solenhofen, 

 Germany in 1861 

 and purchased by 

 the British Museum 

 in 1862. (From De- 

 Beer, Archaeop- 

 terijx lithographica, 

 British Museum of 

 Natural History, 

 1954. ) 



Although birds appeared in the fossil record in the Jurassic, they re- 

 mained rare and insignificant until the Cenozoic era, when they began 

 a great expansion. A few orders, all located on the southern continents, 

 have lost the power of flight and developed powerful running legs, or 

 other adaptations to a purely terrestrial existence. Several orders have be- 

 come adapted to various aquatic niches. Still others have become adapted 

 to a wide variety of land habitats. Altogether, there are twenty-eight 

 orders of extant birds, but it is worth bearing in mind that the birds are 

 taxonomically the best known class of animals, and hence there is a tend- 

 ency to subdivide them more finely than other classes. 



Class Mammalia. Reptiles which diverged in a mammal-like direction 

 occurred in the Permian or even the Pennsylvanian, comprising the order 

 Pelycosauria. These gave rise in the late Permian to a more advanced 

 order, the Therapsida, which in many skeletal characteristics (the only 

 ones which are preserved) approach quite closely to primitive mammals. 



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