The Cambrian explosion was a short period of rapid diversification among early multicellular life, resulting in the evolution of all 35 basic body designs. Scientists have proposed three categories of explanation for why it happened, including extrinsic events, intrinsic mechanisms, and natural ecologies. The Burgess Shale in the Canadian Rockies contains well-preserved fossils from this period, including Aysheaia pedunculata, Hallucigenia, trilobites, and Anomalocaris. The Pre-Cambrian Era was thought to be devoid of large multicellular organisms, but the discovery of the Ediacaran fauna proved otherwise.
The Cambrian explosion was a period of massive diversification and adaptation among early multicellular life, beginning about 542 million years ago and continuing for about a dozen million years, a blink of an eye in evolutionary time. The period was made famous by fossils found in the Burgess Shale in the Canadian Rockies, whose layers were able to preserve specimens very well, even those with soft body parts.
During the Cambrian explosion, all 35 basic body designs underpinning modern life evolved. As such, it was said of Darwin that “nothing distressed him more than the explosion of the Cambrian, the coincidental appearance of nearly all complex organic designs.” If life was meant to evolve incrementally, why did so many new phyla appear at once?
In trying to explain why the Cambrian explosion happened when it did, scientists have focused on three categories of explanation: extrinsic events such as global biochemical upheaval, intrinsic mechanisms such as the dawn of complex genomes, and intrinsic mechanisms such as the aftermath natural ecologies at the time. The Cambrian explosion began about 50 million years after the last of the great global glaciations, a time frame that may have been needed for the complexity to emerge.
Today, the Cambrian explosion doesn’t seem as shocking as when it was first discovered, though it’s still arguably the most important evolutionary period in the history of life. The Pre-Cambrian Era was originally thought to be devoid of almost any type of large multicellular organisms, but the discovery of a class of life called the Ediacaran fauna proved otherwise. Most of the Ediacaran fauna was relatively simplistic and sponge-like, with soft bodies, but more research and fossil hunting is needed before we can get a better look at the fossil record and compare it to that of the Cambrian.
Among the memorable organisms that flourished during the Cambrian explosion were Aysheaia pedunculata, a soft-bodied, caterpillar-like species, Hallucigenia, a creature that looked like a twig with spines, many trilobites, and Anomalocaris, possibly the earliest predator in the world. pinnacle on Earth. The difficulty of classifying many of these organisms adds to the excitement surrounding the period.
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