Amphibian footprints were quite abundant during Carboniferous period
but less so in the Permian, owing to the takeover by the reptiles and the
amphibians’ preference for life in the water. The increase in the number of
reptilian footprints in the Carboniferous and Permian plainly shows the rise
of the reptiles at the expense of the amphibians. Possibly one of the major fac-
tors leading to the superiority of the reptiles was their more efficient mode of
locomotion. The reptiles were also much more suited for living full-time on
dry land, whereas the amphibians had to return to the water periodically.
Populations of amphibians continued to fall during the Mesozoic, with
all large, flat-headed species going extinct. The group thereafter was repre-
sented by the more familiar salamanders, toads, and frogs.The fossil remains of
these amphibians are largely fragmentary because vertebrate skeletons are con-
structed with a large number of bones that are easily scattered by surface ero-
sion. Although the amphibians did not achieve complete dominion over the
land, their cousins the reptiles were destined to become the greatest success
story the world has ever known.THE GREAT COAL FORESTS
During the second half of the Paleozoic, the continents rose and sea levels
dropped. This caused the departure of the inland seas, which were replaced
with immense swamps.About 315 million years ago, extensive forests grew in
the great swamps. These regions formed a vast tropical belt that ran through
the supercontinent Pangaea, which straddled the equator.
By the middle Paleozoic, the terrestrial flora was plentiful and varied.
The most significant evolutionary step was the development of a vascular stem
to conduct water to a plant’s extremities. The early club mosses, ferns, and
horsetails were the first plants to utilize this water vascular system. The early
complex land plants diverged into two major groups.One gave rise to the
lycopods. The other spawned the gymnosperms, which were ancestral to
many modern land plants. The gymnosperms, including cycads, ginkgos, and
conifers,originated in the Permian and bore seeds that lacked fruit coverings.
Eventually, as evolution steadily progressed, great coal forests spread across
the continents.The woodlands included thick stands of seed ferns and true trees,
which were gymnosperms with seeds and woody trunks. By about 370 million
years ago, forests transformed the planet with green, lush vegetation. The
lycopods ruled the ancient swamps. They towered as high as 130 feet and
became the first trees to develop true roots and leaves, which were generally
small.Branches were arranged in a spiral.Spores were attached to modified
leaves that became primitive cones.Their trunks were largely composed of bark
and, for the most part, lacked branches along the length of the tree, lookingHistorical Geology