Understanding Evolution

The Cambrian explosion

From about 570 to 530 million years ago, an evolutionary burst of life forms occurred, often referred to as the "Cambrian Explosion." This marks an important point in the history of life on earth, as most of the major lineages of animals got their starts during the Cambrian Period and have been evolving ever since. If we wound the clock back a little more than half a billion years to the Cambrian, we would find that life then was different from life today:
  • All life was aquatic.
  • Most life was relatively small.
  • Many animals had unusual body layouts.
Many Cambrian animals seem bizarre at first glance, but are actually members of groups that are still around today — such as the arthropods.
A glimpse at life along the Cambrian sea floor
In this investigation, youíll study the fossils and reconstructions of five Cambrian animals and determine which were arthropods and which were not. As you've learned, arthropods inherited a particular set of characters from their common ancestor. These characteristics are often preserved in fossils.

Letís begin our investigation with Sanctacaris.


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Understanding Evolution © 2018 by The University of California Museum of Paleontology, Berkeley, and the Regents of the University of California