2Q6 CALIFORNIA ACADEMY OF SCIENCES [Peoc. 4th Ser. 



INTRODUCTION. 



The gigantic land tortoises do not differ essentially, in any- 

 other respect than in size, from the numerous small species 

 of the genus Testudo which exist in Europe, Asia, Africa, and 

 the Western Hemisphere. They are typical chelonians, modi- 

 fied, as are the other members of the genus, for a purely ter- 

 restrial life, but differing from the ordinary type in their 

 gigantic proportions. Even in size, however, there is no very 

 sharp line of division between the smallest adults of some 

 "gigantic" races and the largest individuals of certain species 

 that are not so designated. 



The geological history of the gigantic tortoises is still but 

 fragmentary. We know that in the Tertiary period they were 

 far more widely distributed than during historic times. Their 

 remains appear as early as the Eocene, but become more num- 

 erous in Miocene and Pliocene formations. They have been 

 found in Nebraska and Wyoming, in France, Germany, Malta, 

 on the Lebanon, in the Sivalik Hills in India, and perhaps 

 also in Brazil. It thus appears that these huge tortoises were 

 formerly widely distributed over the earth ; but it yet remains 

 to be shown whether these giant races are closely related one 

 to another, or have been independently developed from smaller 

 species in situations where climate and food and the absence 

 of enemies were most favorable to their growth. 



In recent and historic times gigantic land tortoises have 

 existed only in certain isolated groups of islands in the Indian 

 and Pacific oceans, where the early explorers found them in 

 almost incredible numbers. The rapidity with which they 

 have disappeared from these islands upon the advent of man, 

 and even upon the advent of the smaller predatory mammals, 

 sufficiently explains their earlier extinction upon all the con- 

 tinents where they formerly occurred. 



Although this paper will be immediately concerned only 

 with the tortoises native to the Galapagos Archipelago, in the 

 eastern Pacific, it will be well to review the history and distri- 

 bution of the tortoises of the islands of the Indian Ocean. I 

 therefore quote a few paragraphs from Dr. Giinther's excel- 

 lent presidential address to the Linnean Society (1898). 



