34 



1USSII. TURTI.KS OK NORTH AMERICA. 



inhabited by these land tortoises, presents only two very restricted areas. Tho at 

 that time it abounded in representatives of the family, some of them of gigantic size, 

 it is now poor in species, there being only 3. Almost the whole of South America 

 is occupied by the family, but there are only 3 known species. Europe claims 

 2 species; while Asia possesses 7. Africa is the headquarters of the family, at 

 least 20 species occurring on that continent. 1 hese belong to 3 recognized genera. 

 The most remarkable feature of the distribution of the Testudinidae is the occurrence 

 of species, some of great size, on islands far away from any large body of land, as the 

 Galapagos Islands and islands in the Indian Ocean. For further discussion of this 

 subject the reader is referred to the treatment of the family on a succeeding page. 

 The geographical distribution of the Pleurodira is represented by fig. 15. It 

 will be seen that the species are almost wholly residents of the torrid and the south 

 temperate zones. A single species has an outlying colony on the Tropic of Cancer, 

 at the head of the Red Sea. The wide distribution of these turtles is not surprising, 

 seeing that they are a very ancient group. The earliest species that are known to 

 belong to the superfamily are described in the present work and come from the 

 Upper Cretaceous of New jersey and New Mexico. Doubtless the group existed 



1 K.. 15. Map showing the distribution of the Pleurodira. 



during the Lower Cretaceous and probably during the Jurassic. In those early 

 days the land masses had connections very different from those now obtaining; 

 and these turtles were able to become diffused to regions now widely separated by 

 deep seas from the original home of the creatures. It would appear more reasonable 

 to suppose that South America had received its original pleurodiran population 

 from North America, by the wav of some Mesozoic land connection; but it is 

 possible that these immigrants reacht that continent from Africa. A considerable 

 number of authors, viewing the subject from different positions, have concluded that 

 there was, during the Mesozoic era, a land connection between South America and 

 Africa, which connection was interrupted about the beginning of the Tertiary. 

 The existence of such a bridge would enable us to account for the occurrence of 

 some closely related species in Madagascar and South America. These species are 

 usually referred to the genus Podocnemis; but Baur regarded the Madagascar 

 species as belonging to the closely related genus Erymnochelys. Two species of 

 Podocnemis are reported from the Middle Eocene beds of the Fayum, Egypt. 



Inasmuch as Pleurodires once occupied a large part of the north temperate zone, 

 it is remarkable that they have not been able to maintain themselves there. The 

 lust and the last that are known to have lived in North America flourisht during 



