N 
FOSSIL TURTLES OF NORTH AMERICA. 
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more than a few common species. Along the western coast of Central and South America, 1n 
situations where they are liable to be earacd down by rivers to the Pacific Ocean, there live 
about 50 genera of lizards. How can it be explained that such a fragment of these has reacht 
the Galapagos Islands? 
An instructive chart, publisht by Dr. Alexander Agassiz (Bull. Mus. Comp. Zool., Xx111, 
pp- 50-74, plate 11) exhibits the floor of the ocean in that region, and demonstrates the presence 
of a tongue of uplift which extends from the Galapagos islands to the Central American coast 
just oak of the Gulf of Panama. It seems therefore probable that at some time in the past, 
evidently after the Oligocene, more probably during the Miocene, there existed a mass of land 
which included the Galapagos Islands and joined narrowly the Central American coast. This 
land mass might be compared to the island of Madagascar, with the long axis at right angles 
with the neighboring continent, instead of parallel with it. Over the narrow bridge tea 
past the ancestors of the present turtles of those islands and a few genera of lizards, together 
with some other animals and sundry plants. The descendants of these invaders have differen- 
tiated and formed a part of the present fauna and flora of the islands. It is not unlikely that 
some genera which invaded that land perisht afterwards. 
When we try to account for the presence of the gigantic tortoises found at one time, but now 
nearly extinct, on the islands of the Indian Oecait we are met with the same difhculties that 
we have been considering. If the conformation of the land and sea was the same as now when 
the ancestors of these tortoises reacht their island homes, they must have been transported over 
the seas for distances varying from 250 to 750 miles. 
The solution of the various problems connected with the distribution of animals and plants 
in southern Africa and southern Asia and the islands of the Indian Ocean have driven many 
geologists, zoologists, and botanists to the conclusion that at one time there was a land connect- 
tion between India and South Africa, across the Indian Ocean. For a masterly discussion 
of this question the reader is referred to the presidential address of Mr. W. T. Blanford before 
the Geological Society of London in 1896 (Quart. Jour. Geol. Soc. Proc., p. 98), and also to 
Giinther’s address already cited. Blanford concludes that there was such a land connection 
as has been mentioned above, that this continued thruout the Upper Cretaceous, and was 
broken up into islands at an early Tertiary date. Dr. Giinther adopts this conclusion and adds 
that ‘‘the slow evolution of this chelonian tvpe (Testudo) which has scarcely changed since 
the Eocene, and its wide distribution over the Northern Hemisphere, justify the supposition 
that it was in existence already before the Tertiary, before the bridge was broken through 
which allowed of its passage southwards or northwards. ’ 
That primitive Testudinide were in existence toward the close of the Upper Cretaceous is 
very probable, but that the genus Testudo had at that time made its appearance there is no 
proof, no probability. We do not know of its existence with certainty before the Upper Eocene 
in Africa and the lowest Oligocene in America. The less advanct forms of eis family, as 
FHadrianus and related genera, may have reacht India or South Africa by the end of the 
Cretaceous, but we have no evidence of this. Hence, unless we are willing to betake ourselves 
to what ought to be our last refuge and hold that Testudo had a polyphyletic origin (using this 
term in its original sense), that the Testudos of America and those of the eastern continents 
sprang independently from Hadrzanus or from the latter genus and another, we must place at 
a later date than the early Eocene the arrival of the ancestors of the gigantic tortoises on Mada- ° 
gascar and the islands of the western portion of the Indian Ocean. 
The conclusion reacht by Mr. Richard Lydekker regarding the time of separation of Mad- 
agascar from the mainland was that this occ urred during the Miocene (Geog. Hist. Mammals, 
p. 223). Mr. Blanford had previously concluded that che depression of 1,000 fathoms or more 
Ww hich led to the formation of the Mozambique Channel had taken place during Phocene or 
Postpliocene times. However, the recent discovery of species that can hardly ‘be separated 
from T estudo, in the Fayum in Egypt, makes it necessary to recognize the fact that members of 
the genus had reacht that continent as early at least as the Upper Eocene. 
Testudinide at their various stages of development are known at earlier dates in North 
America than elsewhere. It seems thereFore! probable that North America was their center of 
distribution. From western North America they may be supposed to have reacht Central 
America and to have migrated thence to the present Galapagos Islands, From western North 
