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Chapter 26 The Tree of Life: - page 16 / 18





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However, macroscopic life in the form of plants, fungi, and animals did not colonize land until about 500 million years ago, during the early Paleozoic era.

The gradual evolution from aquatic to terrestrial habitats was associated with adaptations that allowed organisms to prevent dehydration and to reproduce on land.

For example, plants evolved a waterproof coating of wax on their photosynthetic surfaces to slow the loss of water.

Plants colonized land in association with fungi.

In the modern world, the roots of most plants are associated with fungi that aid in the absorption of water and nutrients from the soil.

The fungi obtain organic nutrients from the plant.

This ancient symbiotic association is evident in some of the oldest fossilized roots.

Plants created new opportunities for all life, including herbivorous (plant-eating) animals and their predators.

The most widespread and diverse terrestrial animals are arthropods (including insects and spiders) and vertebrates (including amphibians, reptiles, birds, and mammals).

Terrestrial vertebrates, which include humans, are called tetrapods because of their four limbs.

Earth’s continents drift across the planet’s surface on great plates of crust.

Earth’s continents drift across the planet’s surface on great plates of crust that float on the hot, underlying mantle.

Plates may slide along the boundary of other plates, pulling apart or pushing against each other.

Continental plates move slowly, but their cumulative effects are dramatic.

Mountains and islands are built at plate boundaries or at weak points on the plates.

Plate movements have had a major influence on life.

About 250 million years ago, near the end of the Paleozoic era, all the continental landmasses came together into a supercontinent called Pangaea.

Ocean basins deepened, sea level lowered, and shallow coastal seas drained.

Many marine species living in shallow waters were driven extinct by the loss of habitat.

The interior of the supercontinent was severe, cold, and dry, leading to much terrestrial extinction.

During the Mesozoic era, 180 million years ago, Pangaea began to break up.

Lecture Outline for Campbell/Reece Biology, 7th Edition, © Pearson Education, Inc. 26-16

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