138 The History of the Earth: Supplemental Guide 7A | Fossils
Show image 7A-6: Cooksonia fossil
At about this same time, the fossil record estimates that the fi rst
plants appeared on land. Back then, there was no soil on the land,
because soil contains dead, decayed plants. Since these were the
fi rst plants on land, no plants had yet died in order to create soil.
The fi rst plants did not have the same characteristics as plants
today. These plants were less than half an inch tall and they had no
roots, leaves, fl owers, or seeds, but they were plants nevertheless.^9
Show image 7A-7: Fish fossils
Soon came the Age of Fish. Many different types of fi sh ruled
the waters.
Show image 7A-8: Tetrapod recreation
Also during this time, plant and animal life on land began
to spread rapidly. The fi rst soils developed on land, allowing
new types of plants with leaves, stems, and roots to grow. With
new plants came new land creatures ready to eat those plants.
Tetrapods, the fi rst amphibians, made their way onto the beaches.
An amphibian is an animal that lives part of its life in water and
part on land, like a frog.
Paleontologists have found many tetrapod fossils. An artist drew
this picture using a tetrapod fossil, which shows what a real tetrapod
might have looked like. Do you think any of this tetrapod’s body parts
look like they belong to a fi sh?^10
Show image 7A-9: Fern fossil
Then, lush forests full of trees and plants, such as ferns, began
to grow.
Show image 7A-10: First reptiles
As forests increased, so too did the variety and sizes of
animals. The fi rst giant reptiles appeared. Of course, the one in
this picture—called a dimetrodon—is just a model that someone
made, but they based this model on fossilized dimetrodon bones
found in the earth. Paleontologists call the body part sticking up
on its back a sail because it looks like the sail on a boat.9 [Show the height of less than half
an inch with a ruler.]
10 [Pause for students to answer.]