Geology Reference
In-Depth Information
ure. I provide more information about reptiles and the evolution of early mammals in
Chapter 20.
Reptiles may have been the first animals to dominate the land, but they were not the
first living creatures on land. Long before amphibians ventured out of the water, plants
had established themselves on land and were living alongside swarms of insects. Keep
reading to find out more about what the fossil records tells scientists about life on land
in the Paleozoic.
Planting Roots: Early Plant Evolution
The first land plants must have started as
aquatic
(water-living) plants. In or-
der to survive on land, plants need a supportive structure and a way to move wa-
ter through their system. A material called
cellulose
in plant cell walls provides
that structure, and specialized cells function to transport water throughout a
plant. Plants with this special tissue are called
vascularplants.
Nonvascular plants
still survive today, such as mosses and fungi, but they live in moist areas and do
not grow very large because they lack vascular tissue.
During the Paleozoic, land plants experienced many important changes. By the middle
Paleozoic, woody tissue (made of a material called
lignin
and much stronger than cellu-
lose) in some plants allowed them to grow very tall. Fossils indicate that some of them
were as large as modern trees, although they didn't reproduce using pollen and flowers.
(These features evolved after the end of the Paleozoic, in the Mesozoic.) These early
plants reproduced through
spores,
similar to modern fern species.
During the Carboniferous period (359 to 299 million years ago), ancient tree-like plants
such as
Lepidodendron, Sigullaria,
and
Calamites
grew abundantly in low-lying swampy
environments. These dense areas of vegetation, called
coal swamps,
were later pre-
served and transformed into the sedimentary rocks that provide modern fossil fuel re-
sources such as coal and oil. Figure 19-7 illustrates some of the common plants of the
Carboniferous coal swamps.
By the end of the Paleozoic, modern plant types including ferns and gymnosperms had
begun to appear. Gymnosperms are plants that reproduce using pollen and seeds, but
without flowers. Gymnosperms include modern plants such as
conifers,
or cone-bearing
trees and cycads. Table 19-1 summarizes when these and other major steps in plant
evolution occurred.
