How Do Living Things of the Past Compare with Those of Today? Thousands of fossils have been found at Thomas Farm in central Florida. More are still being discovered! Lesson 3

Lesson 3 Vocabulary 1. Fossil —evidence of a plant or an animal that lived long ago. 2. Extinction —all members of a certain kind of living thing have died.

Lesson 1 (Page 114) A fossil is evidence of a plant or animal that lived long ago. Footprints that formed when an animal stepped in mud are one kind of fossil. Over a long time, the mud hardened into rock. Footprints tell us about an animal’s size. Many fossils are bones that became buried before they could decay. Minerals replaced the bones, but the shapes remain. Scientists compare these fossils with the footprints and bones of animals that are alive today. Using the comparisons, they can infer how animals have changed.

Although they are completely unrelated, fossils show that the triceratops and today’s rhinoceros share the same body shape and a horned nose. Dinosaurs were reptiles, while rhinos are mammals.

Lesson 3 (page 115) A few animals, such as turtles, are much like ones from long ago. Others are very different from now. By a careful study of their fossils, scientists can link animals of long ago with those of today. However, many ancient animals are now gone. By the early part of the 20 th century, the coelacanth fish shown in this fossil was thought to exist no longer, but a live coelacanth was caught near South Africa in 1938.

Video about Fossils

Lesson 3 (Page 116) You might have found a plant fossil on a flat rock in a park or in your own backyard. Some of these fossils were formed when plant leaves fell on muddy ground millions of years ago. The leaves made an impression in the mud. When the mud dried, the imprint of the leaf was still there. This imprint shows the size, shape, and details of the leaf.

Lesson 3 (Page 116) Like some animals of long ago, many plants of long ago have disappeared. Scientists know about them only because of fossils. Many other plants have survived, but they have changed over time.

Lesson 3 (Page 117)

Bristlecone pine trees were growing 100 million years ago. The oldest tree living today is almost 5,000 years old! Fossils show that trees have changed very little.

Lesson 3 (Page 118) Extinction means that all the members of a certain kind of living thing have died. Extinction can happen when a habitat changes. For example, a habitat may become drier. Then the habitat may no longer meet the needs of some living things. Plants in these places die. Animals must find new places to live or they will die, too.

Extinction Video

Lesson 3 (Page 118) Extinction can also happen for other reasons. One reason is an increase in predators. Another is a decrease in the food supply. About 65 million years ago, 70% of all living things became extinct. It is possible that an asteroid hit Earth, changing the environment and reducing the food supply.

Lesson 3 (Page 118) Extinction is still happening. People may cause extinction when they cut forests or fill in wetlands. This change in the environment can cause living things to lose their habitats.

Lesson 3 Review! 1. Fossil —evidence of a plant or an animal that lived long ago. 2. Extinction —all members of a certain kind of living thing have died.