Biology  5/e   Raven/Johnson
	Student   Online Learning Center

Major features of evolutionary history: The earth is about 4.6 billion years old. The oldest fossils of living things are about 3.5 billion years old. All life evolved in the sea until about 410 million years ago, when invasion of the land began. Throughout the history of living things, continental drift has had a profound influence. Continental movements have caused extinction through loss of habitat, and have caused accelerated evolution by increasing competition through formation of land bridges and isolation through loss of land bridges. Throughout all continental migrations, adaptation to climatic change by the living "passengers" was often the key to survival.

Classification: Three domains are recognized: Archebacteria, Eubacteria, and Eukarya. There are six recognized kingdoms: Archebacteria, Eubacteria, Protista, Fungi, Plantae, and Animalia. Kingdoms are divided into phyla (sometimes called divisions in plants,) which are subdivided into classes. Classes are divided into orders, and in turn, families, genera, and species.

Body plans of bilaterally symmetrical animals: Bilaterally symmetrical animals have one of three body plans.

1. Acoelomate, having no body cavity surrounding the viscera.
2. Pseudocoelomate, having a body cavity with one layer of mesoderm between the endoderm of the viscera and the ectoderm.
3. Coelomate, having, in addition to the structure of the pseudocoelomate, a second layer of mesoderm surrounded by the body cavity.

Copyright ©1998 The McGraw-Hill Companies. All rights reserved. Any use is subject to the Terms of Use and Privacy Policy.
McGraw-Hill Higher Education is one of the many fine businesses of The McGraw-Hill Companies.
For further information about this site contact mhhe_webmaster@mcgraw-hill.com.