THE EVOLUTION OF THE MAMMALIA 
W. B. SCOTT, Princeton University. 
( Concluded from July number. ) 
A second series of perissodactyls, which is still represented at 
the present day, is that of the rhinoceroses. The origin of this 
group is still veiled in obscurity, for the earliest unquestionable 
representatives of the main or direct series appear in the lower 
Oligocene of Europe and North America. There are, however, 
several more ancient and very imperfectly known genera, which, 
when more complete specimens of them have been recovered, 
may very well prove to be the ancestors for which we are still 
seeking. At the present time, the rhinoceroses are verging 
toward extinction, and are found only in the warmer parts of 
Africa and southern Asia; but in former periods they ranged freely 
all over the northern hemisphere, and were not only very abun- 
dant individually, but were also exceedingly varied ; the trunk 
supporting many flourishing and vigorous branches. 
Three principal divisions or series of the rhinoceros group 
may be readily distinguished, though it is an extremely difficult 
task to marshal all the many genera and species in orderly array, 
and to make out their relationships to one another. What may 
be called the main series, is that leading to the modern and still 
existing forms, but it is a highly ramified series, giving off branches 
and twigs at almost every stage of its history. The principal 
development of this series took place in the Old World ; the other 
two series, now entirely extinct, being North American, either 
Copyright, 1901, by Frederick A. Richardson. 
