The "Cambrian Explosion"
The Cambrian Period (542-488 million years ago) began with one of the most important evolutionary events in the history of the Earth: the "Cambrian Explosion" of life in the oceans. Over about 20 million years, the variety of animals in the oceans increased dramatically. By the end of the Cambrian, all of the major groups of animals, including the vertebrates, had evolved. A major evolutionary breakthrough was the origin of hard shells that gave animals protection from predators.
At most places, the Cambrian fossils that we find are those that had hard shells when they were alive.Trilobites (extinct arthropods) are particularly common. We know from rare cases of unusual fossilization that there were many other kinds of animals living in the Cambrian seas. The Burgess Shale of western Canada preserved animals with delicate shells, or which lacked a shell all together. These animals would decay quickly after death and are not normally preserved. The Burgess Shale gives us a window on the Cambrian world. It shows us that trilobites lived with an even wider variety of unusual arthropods.Cambrian communities reconstructed from information from the Burgess Shale and other examples of unusual fossilization include a variety of animals (above). In Oklahoma, we find only the fossils of hard-shelled animals like trilobites, brachiopods and crinoids. What we know of communities of the Cambrian seas of our state is therefore limited. There were probably many soft-bodied animals in these communities that are unrecorded as fossils. As a result our community reconstructions (below) look relatively empty.
Can I find Cambrian fossils in Oklahoma?
You can find Cambrian fossils in limestones of the Arbuckle Mountains and in the hills to the north of the Wichita Mountains.