THE PALEONTOLOGIC RECORD 149 
malian skeleton has brought about many morphological modifications 
from those shown in the Batrachia and Reptilia. We find the skull 
loses the prefrontal and postfrontal bones, the mandible is simplified, 
the limb bones show a development of terminal epiphyses with ossifica- 
tion to the center of the vertebrae and the bones of the pelvic arch are 
ossified. From the beginning of the Tertiary time a marvelous variety 
of morphological characters appears, and without the fossil types we 
should have but an inadequate conception of this great phylum. 
The contributions of paleobotany to morphology are in some re- 
spects quite as striking as those of paleozoology. 
The fossil Thallophytes have not furnished any very striking varia- 
tions from their present morphological features, while the bryophytes 
are scarcely represented as fossils except in very recent deposits. 
The remaining phyla, the Pteridospermatophytes, the Pteridophytes 
and the Spermatophytes have their oldest known beginnings as far 
back as the Devonian and their study has enormously widened the 
bounds of plant morphology. 
The Pteridospermatophytes, which are confined to the Paleozoic, 
are in habit and vegetative morphology ferns—in methods of repro- 
duction and in the morphology of their reproductive organs typical seed 
plants. They alter our whole conception of ferns and seed plants and 
in their significance are comparable to archetypal vertebrata, the acqui- 
sition of the seed habit in plants and the vertebral column in animals 
probably marking the culmination of the transfer of vital activity from 
aquatic to terrestrial conditions. 
In the Pteridophytes the extinct Paleozoic class, the Sphenophyllales, 
is significant, since the morphology of the distinct lycopod and Hqut- 
setum lines seems to merge in this group. The lycopod type, itself 
represented in the existing flora by six or seven genera of herbaceous 
plants, monotonously uniform in their morphology, is found in the 
Paleozoic to constitute one of the chief units in the arborescent flora 
with numerous species of complex organization, whose stem, foliar and 
reproductive morphology was quite unknown to botanists (Lepido- 
dendron, Sigillaria, etc.). The Hquisetum type furnishes a like 
case. With few existing species of minor importance and uniform 
morphology we find in the Paleozoic a host of forms, many of them 
arborescent and of varied and complex structure (Calamites, Archao- 
calamites, etc.). Similar examples could be drawn from the fossil 
representatives of the true ferns. 
In the Spermatophytes another wholly extinct class, the Cordaitales, 
embraces a curiously organized group of conifers extending back to the 
oldest horizons from which land plants are found, and continuing to 
the close of the Paleozoic as one of the most abundant as well as the 
highest type of pre-Mesozoic plant. In the older Mesozoic we find two 
