11 



Eeptiles and Birds form the next great division of ver- 

 tebrates, the Sauropsida, and of these the Reptiles are the older 

 type, and may be first considered. While it may be stated 

 with certainty that there is at present no evidence of the exist- 

 ence of this group in American rocks older than the Car- 

 boniferous, there is some doubt in regard to their appearance 

 even in this period. Various foot-prints which strongly resem- 

 ble those made by Lizards ; a few well preserved remains similar 

 to the corresponding bones in that group ; and a few charac- 

 teristic specimens, nearly identical with those from another 

 order of this class, are known from American Coal Measures. 

 These facts, and some others which point in the same direction, 

 render it probable that we may soon have conclusive evidence of 

 the presence of true Eeptiles in this formation, and in our over- 

 lying Permian, which is essentially a part of the same series. 

 In the Permian rocks of Europe, true Reptiles have been 

 found. 



The Mesozoic Period has been called the Age of Reptiles, 

 and during its continuance some of the strangest forms of rep- 

 tilian life made their appearance, and became extinct. Near 

 its commencement, while the Triassic shales and sandstones 

 were being deposited, true reptiles were abundant. Among 

 the most characteristic remains discovered are those of the 

 genus Belodon, which is well known also in the Trias of 

 Europe. It belongs to the Thecodont division of Reptiles, 

 which have teeth in distinct sockets, and its nearest affinities 

 are with the Crocodilia, of which order it may be considered 

 the oldest known representative. In the same strata in which 

 the Belodonts occur, remains of Dinosaurs are found, and it is 

 a most interesting fact that these highest of reptiles should make 

 their appearance, even in a generalized form, at this stage of 

 the earth's history. The Dinosaurs, although true reptiles in 

 all their more important characters, show certain well marked 

 points of resemblance to existing birds of the order Ratilce, a 

 group which includes the Ostriches; and it is not improbable 

 that they were the parent stock from which birds originated. 



