542 million years ago, nearly all modern animal phyla burst on the scene in an explosive radiation that has come to be known as the Cambrian explosion. However, this rapid evolution of new organisms appears to have come at the expense of some of Earth’s earliest life forms, and scientists have now discovered a reason why.
The first complex life on Earth came in the form of a number of species of largely immobile, tube-like organisms known as the Ediacarans. After a comfortable 37 million years of existence, these creatures suddenly disappear from the fossil record at the onset of the Cambrian period.
Evidence for this being the result of an environmentally-driven mass extinction is sparse – studies by Dr Mark Laflamme of the University of Toronto yielded no geochemical signatures of low-oxygen conditions or environmental turmoil. Equally, the fact that soft-bodied Cambrian animals fossilised well suggests their disappearance is not a result of a patchy fossil record.
Instead, Simon Darroch of the Smithsonian Institute believes his team have found evidence for a significant role of biological factors in the Ediacaran extinction.
“Modern animals are ecosystem engineers. They alter the environment, burrow into sediments and prey on each other,” he says as he explains the rationale behind his theory.
If Cambrian animals drove the extinction of the Ediacarans, the fossil record should provide evidence that their communities were struggling. Indeed, evidence, such as low species richness, does suggest that the communities “look very stressed”. Sea-anemone-like traces in the most recent Ediacaran fossils hint at the presence of a similar predator that may have fed on these organisms.
“There were probably predators in the late Ediacran,” says Darroch. Coupled with the stressed communities of these animals, he believes this adds up to pretty robust evidence that new species either ate the old ones, or destroyed their habitat.