Key findings about Cambrian animals
- Animals of the Cambrian period experienced one of the greatest evolutionary surges in history, known as the Cambrian Explosion.
- Animals of the Cambrian period probably originated as worms or worm-like organisms. However, by the end of the period, these animals had developed legs, jaws, teeth, a primitive spine, and compound eyes.
- The largest animal of the Cambrian period belonged to the Anomalocaris group. They were ferocious predators and could reach three feet in length. Although remains of Cambrian animals exist today, none of the species that existed then are alive today.
The Cambrian, the first period of the Paleozoic era, lasted about 50 million years. For creatures like us, who live on average about 80 years, that seems like a long time. But in geological time this is just a blip. The US National Park Service website puts it this way: If you think of Earth's geological history as a calendar year, the Cambrian period takes only four and a half days.
In this relatively short period, life on Earth underwent the greatest evolutionary surge it has ever known, earning the event the nickname “Cambrian Explosion,” according to the Natural History Museum. Over the three billion years that life has existed on Earth, life has consisted primarily of single-celled organisms.
Just before the Cambrian explosion, early animals similar to sponges or jellyfish probably existed. They eventually evolved into tiny worms, explains Eric Sperling, a scientist at Stanford University who studies biogeochemistry.
“All the different animals found in the fossil record evolved from relatively simple worms,” he says.
Read more: 518 million years ago, the largest and most dangerous predators were… worms?
Animals that lived during the Cambrian period
By the end of the Cambrian, fossil record animals are depicted with legs, jaws, teeth, a primitive spine and compound eyes. However, these animals did not simply develop new anatomical structures. They developed new ways of being in the world.
“They made shells and skeletons from a variety of biomaterials. They adopted a variety of lifestyles, living in sediments, rising up and swimming in the water column. It was not only an explosion of diversity, but also an ecological explosion,” says Sperling.
The most common (and best known) animals to emerge from the Cambrian explosion were trilobites. Trilobites They were arthropods, a type of invertebrate that includes insects, spiders and crustaceans such as shrimp and crabs, according to the Natural History Museum. The upper part of the trilobite's body was armored and well petrified.
Even amateur fossil hunters can find plenty of them. Fossils of their soft underbelly are not so common. However, scientists know that they had jointed legs and compound eyes.
Read more: The Spinetooth Worm and Other Creatures Lived in the Grand Canyon 500 Million Years Ago
The largest animal of the Cambrian period
For the most part, Cambrian animals were fairly small creatures, but a group called AnomalocarisAccording to the Natural History Museum, the arthropod phylum was about 60 centimeters (about 23 inches) long, and may have been around 3 feet (1 meter). “These were the giants of the Cambrian world,” says Sperling.
Terrible predator Anomalocaris had good eyesight, which made him a good hunter. It probably grabbed soft-bodied prey with its spiny hands.
Pikaia, a slender fish-like creature with a primitive backbone, originated in the Cambrian and may be the distant ancestor of all vertebrates, including us, according to a study published in Cell biology.
Although all animals alive today are descended from creatures that appeared in the Cambrian period, not a single species from that period still exists.
What is the Cambrian period known for?
Although scientists have learned a lot about the Cambrian period from the fossil record, they are less certain about what caused this burst of evolution.
“There are as many hypotheses about the causes of the Cambrian Explosion as there are areas of research,” laughs Sperling. “It's one of those events where everyone seems to see the answer as their own area of research, like if you had a hammer, everything would look like a nail.”
One of the most common hypotheses is that a sudden increase in oxygen levels triggered all this new life to arise. However, there is little evidence of a significant increase in oxygen content. But perhaps it didn't require much magnification.
In an article published in the magazine NatureSperling and his colleagues showed that most animals at that time lived in shallow waters, where wind and waves could oxygenate the water, although oxygen levels did not change at greater depths. Sperling says a small increase in oxygenation could be enough to cause large ecological changes.
Whatever caused it, the Cambrian period was a time of fascinating evolution, and it can tell us a lot about the history of life on Earth—and potentially, Sperling says, about the possibility of life on other planets.
He says the most interesting questions posed by the Cambrian explosion are: “Was it supposed to happen? Were animals inevitable on Earth?” Answers to these questions could help us search for life on other planets whose environments could support large, complex, multicellular life.
Read more: Scientists have found fossilized arthropod brains 500 million years old
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