Discuss the evolutionary history of the animal kingdom

Figure 1. An artist’s rendition depicts some organisms from the Cambrian period.

Many questions regarding the origins and evolutionary history of the animal kingdom continue to be researched and debated, as new fossil and molecular evidence change prevailing theories. Some of these questions include the following: How long have animals existed on Earth? What were the earliest members of the animal kingdom, and what organism was their common ancestor? While animal diversity increased during the Cambrian period of the Paleozoic era, 530 million years ago, modern fossil evidence suggests that primitive animal species existed much earlier.

What You’ll Learn to Do

• Describe the features that characterized the earliest animals and when they appeared on earth
• Explain the significance of the Cambrian period for animal evolution and the changes in animal diversity that took place during that time
• Discuss the implications of mass animal extinctions that have occurred in evolutionary history

Learning Activities

The learning activities for this section include the following:

• Pre-Cambrian Animal Life
• The Cambrian Explosion
• Post-Cambrian Evolution
• Self Check: The Evolutionary History of the Animal Kingdom