CHAPTER II 



PEDIGREES AND RELATIONSHIPS 



Reptiles and their relationship to warm-blooded Vertebrates : the origin of 

 reptiles. The Theromorpha and their relation to the Mammalia : the Ornitho- 

 morpha and their relation to birds. The tuatera : crocodiles and their ancestry : 

 tortoises and turtles: flying reptiles: dinosaurs: snakes and lizards : geological 

 history: plesiosaurs and ichthyosaurs : numerical strength. 



IN the preceding chapter it has been mentioned that reptiles 

 appear to have given rise on the one hand to mammals and 

 on the other to birds ; they are thus the parental stock of 

 all warm-blooded vertebrates. Modern authorities are generally 

 agreed that reptiles themselves are derived from the primeval 

 salamanders, or stegocephalian amphibians, and that the evolu- 

 tion of the class took place during or about the Lower Permian 

 period, that is to say towards the close of the Pakeozoic era. 

 There is, however, some difference of opinion as to whether 

 the origin of reptiles from amphibians was single or dual (mono- 

 phyletic or diphyletic), and also as to the exact limitations of 

 the two classes. Dr. H. Gadow, for instance, in the Cambridge 

 Natural History includes in the Reptilia certain Permian forms, 

 such as Eryops and Cricotus, which are usually regarded as stego- 

 cephalian amphibians, to form a group termed the Proreptilia, 

 which is regarded as the starting-point from which all true 

 reptiles have sprung. He also classes as reptiles the so-called 

 Microsauria, which are likewise generally considered to be 

 stegocephalians, brigading them with the Rhynchocephalia 

 {Protorosaurus, Sphenodon, etc.) to form a group — Prosauria — 

 connecting the Proreptilia with other reptiles. He thus pos- 

 tulates a monophyletic origin for the Reptilia in general. 



On the other hand, another authority, Mr. G. A. Boulenger, 

 in an article published in the P Proceedings of the Zoological 

 Society of London for the year 1904 refused to admit Dr. 

 Gadow's Proreptilia and the Microsauria into the class of 



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