Biology 2010 Student Edition

Published by Prentice Hall
ISBN 10: 9780133669510
ISBN 13: 978-0-13366-951-0

Chapter 26, Animal Evolution and Diversity - Standardized Test Prep - Page 779: 8



Work Step by Step

The first true mammals appeared at the end of the Triassic Period about 220 million years ago. These first mammals were small and shrew-like. They mostly were nocturnal. Following the mass extinction of the dinosaurs, mammal groups began to expand.
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