96 THE MAIN CURRENTS OF ZOOLOGY 



that for the duration of many additional seons, the 

 only living vertebrates were Fishes. From the fishes 

 were gradually evolved the amphibians, the reptiles, 

 the birds and, finally, the mammals. All these 

 changes requiring immense stretches of time took 

 place before the advent of man. 



From tune to time the fossil series exhibits interest- 

 ing connecting links such as the curious tailed and 

 toothed bird, the archaeopteryx, showing structural 

 relations between reptiles and birds. 



The science of fossil remains is not only an off- 

 shoot of zoology but as before stated it was founded 

 by zoologists; Cuvier being the recognized founder 

 of vertebrate and Lamarck of invertebrate paleontol- 

 ogy. This science was extensively developed by 

 Zittel, the paleontologist of Munich, and by Cope 

 (Fig. 20), Leidy (Fig. 21), and Marsh in the United 

 States as well as by more recent workers. 



Extensive progress has been made within the past 

 twenty-five years in observations of the fossil animals 

 and among other advances the genealogy of several 

 living families of mammals has been traced. Notable 

 studies have been made on the ancestry of Camels, 

 Elephants, etc. The most thoroughly known an- 

 cestral history is that of the horse. The zoological 



