316 
KIRTLEY F. MATHER 
and lakes. They are among the first of many creatures who 
forsook the land, modified their legs into swimming apparatus 
of one form or another, mimicked the fishes in the shape of their 
bodies, and returned to the water which their remote ancestors 
had long before deserted to invade the new terrestrial domain. 
Interestingly enough, these fresh-water reptiles are known to 
have lived during the closing epochs of the Paleozoic Era only 
in South America and South Africa; how they travelled from 
the one continent to the other, they could not exist in the salt 
water of the sea, is one of the unsolved problems of the paleon- 
tologist. They, tl)o, had their day and ceased to be, and their 
whole life history was closed before the Age of Reptiles began. 
But several of the reptilian strains were more successful or 
more fortunate; they persisted, to become not only the progeni- 
tors of the varied saurian masters of the Mesozoic Era but of the 
higher class of birds and still higher mammals as well. Clumsy,, 
crawling creatures they were, with much bone and little brain 
in front of their squat shoulders. Heavy in body, short in leg^ 
many of them could little more than drag their trunks over 
the sand or through the mud. For some of them the vast 
arid tracts seemed purposely designed, and there they multiplied 
in number, deployed into several different evolutionary strains 
and slowly, conservatively perfected that complete adaptation 
to the dry land which was necessary to the further progress of 
life. Truly reptilian in habits, the cold blood which coursed 
sluggishly through their veins was not shocked by the icy drafts 
of the glacial climates. The disastrous episodes which closed 
the Paleozoic Era left them unscathed; the rush of the stream of 
life swept them forward to the high destiny which they realized 
in the Age of Reptiles. 
But their success was not achieved as a result of the revolu- 
tionary events which mark the transition between those two 
eras. They had already won for themselves their leading parts 
in the drama of life. Long ages of quiet unassuming preparation 
had preceded those spectacular moments. The slow and steady 
progress which they were making seems simply to have 
been accelerated by the very adversities of -that comparatively 
