The Cambrian

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In the beginning, there was Gondwanaland...

A hostile environment of tectonic activity causing earthquakes and volcanoes to erupt ensued. The continents of Gondwanaland were just waiting to break apart and come crashing back together. Huge mountains speared from the earth and the world experienced great climatic change. These extreme conditions helped pave the road to the Cambrian Explosion not only by mixing oxygen into the ocean, but forcing creatures to adapt quickly to the harsh surroundings.

History

The word ‘Cambrian’ came from the Roman name for Wales where the first geological studies were conducted on the period’s strata or layers of soil where its fossils are found. It began 543 million years ago and ended 43 million years later. The Cambrian Period is also known as Biology’s Big Bang and the Cambrian Explosion because of its great diversity of life. Here was the first appearance of limbs and segmented bodies. The first organisms to be predators, and to develop shells, jaws, claws, and teeth appeared here as well. We see varied multicellular and complex life that spent most of the time on the muddy sea floor. No creatures traveled by land, all were aquatic. It was during this time that ancestors of all animals which fly, swim, and crawl evolved and appeared in less than 10 million years; few new structural models emerged from Cambrian bodies. But scientists estimate that evolution requires 75 million years to show change. ‘Explosion’ seems a fitting word to describe the speed at which life evolved during the Cambrian.

Fauna

From fossil studies (mainly from the Burgess Shale), the Cambrians were scavengers, mud eaters, and micropredators. Herbivores represented most of Cambrian life, but some predators existed. These predators are believed to be responsible for the sudden appearance of complex life (but that will be discussed in the Theoretical section). Arthropods thrived and were a diverse group who are the distant relatives of crabs, lobsters, spiders, and flies. Worms were abundant and numerous sponges and brachiopods, the most common shellfish, covered the sea-bed. Also present were the earliest echinoderm sea lilies and primitive mollusks which gave way to clams, snails, and mussels. Simply too many animals!

Alien Life

The sudden burst of life was new and strange. We see our first ancestor, the Pikaia also called Yunnanozoon, which was an early chordate, the group containing vertebrates. As mentioned before, worms were abundant such as the Canadia, a polychaete worm, and Ottoia, a burrowing worm, belonging to the priapulid or predatory worm group. Other worm-like creatures were the Hallucigenia (not be confused with hallucinogen) and the Aysheia; they resemble today’s caterpillars. The Anomalocaris was the fiercest predator. You can call him king of the sea. The Opabinia was a five-eyed monster that roamed the ocean floor with a protruding nozzle. And we can’t forget the

Trilobites, one of the first arthropods, that progressed for the next 320 million years! Another arthropod was the Marella, well known for its many jointed legs. Other life forms included the Wiwaxia, a spike-covered and sluglike animal, and Conodonts, creatures believed to be early chordates bearing tiny toothlike shapes.

Cambrian Mysteries

The Cambrian Period was strange and exciting, but it was also a time of confusion. A confusion that has lasted for 150 years with scientists baffled over the Cambrian’s sudden explosion. No widely accepted theory explaining the burst of life exists and thus, it is fitting that we end with these questions. Can you find an answer to the problems? What caused biology’s Big Bang to occur so rapidly? Why haven’t there been any repeats of successful evolution and diversity? Why are there no new phyla after Cambrian?