Cambrian period 543-490 million years
Introduction
The Cambrian Period marks the beginning of the Paleozoic Era. This period gets its name from a place in Wales where the first examples of this type of ancient life was found. The period lasted for nearly 53 million years, from about 543 million years ago until 490 million years ago. The Cambrian Period marks an important point in the history of life on earth; it is the time when most of the major groups of animals first appear in the fossil record. This event is sometimes called the "Cambrian Explosion", because of the relatively short time over which this diversity of forms appears. It was once thought that the Cambrian rocks contained the …show more content…

Trace fossils made by animals also show increased diversity in Cambrian rocks, showing that the animals of the Cambrian were developing new ecological niches and strategies -- such as active hunting, burrowing deeply into sediment, and making complex branching burrows. Finally, the Cambrian saw the appearance and/or diversification of mineralized algae of various types, such as the coralline red algae. This does not mean that life in the Cambrian seas would have been perfectly familiar to a modern-day scuba diver! Although almost all of the living marine phyla were present, most were represented by classes that have since gone extinct or faded in importance. Cambrian echinoderms were predominantly unfamiliar and strange-looking types such as early edrioasteroids, eocrinoids, and helicoplacoids. The more familiar starfish, brittle stars, and sea urchins had not yet evolved, and there is some controversy over whether crinoids (sea lilies) were present or not. Even if present, crinoids were rare in the Cambrian, although they became numerous and diverse through the later Paleozoic. And while jawless vertebrates were present in the Cambrian, it was not until the Ordovician that armored fish became common enough to leave a rich fossil record. Other dominant Cambrian invertebrates with hard parts were trilobites (like the one on the upper left, Nevadella from the