For most of the nearly 3.5 billion years of documented life on Earth, creatures were simple, dominated by organisms such as bacteria, algae and fungi (SN: 10/13/18, p. 10).
Then, beginning about 541 million years ago, life quickly diversified into an array of new, complex forms. This flourishing, called the Cambrian explosion, took place within about 25 million years. Fossils from the period have been preserved in rocks at more than 50 known sites worldwide, the most famous of which is Canada’s Burgess Shale, discovered in 1909.
At five standout Cambrian sites, hundreds to thousands of different species were buried in the soft mud of long-ago seafloors. Rapid burial led to the exceptional preservation of soft-bodied animals as well as of soft tissues, such as brains, guts, eyes and skin, that typically don’t fossilize well. A newly reported site, Qingjiang in China, holds a wealth of exquisitely preserved soft-bodied animals such as jellyfish and comb jellies.
Here are some examples of the remarkable diversity of weird and wonderful Cambrian life found at these five sites:
Canada’s Burgess Shale (1909)
508 million years old
Marrella fossils were some of the first found at the Burgess Shale and are the most common. At first labeled trilobites, the small, spiny sea creatures were later revealed to be a distinct type of arthropod.
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China’s Chengjiang (1984)
518 million years old
Fuxianhuia fossils offer what may be the best-known view of a Cambrian brain, tucked beneath a head shield. The organ could have evolved to help the marine arthropods process detailed visual information.
China’s Qingjiang (2007; reported 2019)
518 million years old
The detailed preservation of this ctenophore, or comb jelly, shows rows of combs, which are plates of fused hairlike structures called cilia. Modern comb jellies use the combs to propel themselves through the water.
Australia’s Emu Bay Shale (1979)
514 million years old
Anomalocaris’ compound eyes (one shown) sported a stunning 16,000 lenses, at least. Few other arthropods, living or extinct, have had as many lenses (details shown in inset) as this marine predator.
Greenland’s Sirius Passet (1984)
515 million years old
Meet Halkieria, a scaly, sluglike creature with bivalve shells on the front and rear of its body. The animal continues to defy classification; it has been linked to early mollusks and brachiopods, also known as lamp shells.