An article published in the journal “Palaeogeography, palaeoclimatology, Palaeoecology” describes a study that offers new evidence supporting the theory that the first animals caused the first major mass extinction that took place on Earth. According to a group of researchers led by Simon Darroch of Vanderbilt University, the animals species that emerged in the so-called Cambrian explosion altered their environment in such a way that they caused that extinction.
About 540 million years ago, the so-called Ediacaran fauna (photo of Dickinsonia costata ©Verisimilus) existing at the time became extinct. Those creatures were very different from the ones existing earlier than 600 million years ago and those that existed after their extinction. For this reason, their classification keeps on being a source of controversy even though today many fossils belonging to the Ediacaran fauna are available.
According to Simon Darroch and his colleagues, the discovery of one of the best examples of communities where Ediacaran fauna and animals were mixed provides the best evidence of the ecological association of these two groups. In southern Namibia, fossils were found of what were defined mixed communities of various species some of which appear to be of Ediacarans and others of animals.
The fossils found are the best of this type. So far, the evidence of the existence of animals and Ediacarans that lived in the same ecosystem were limited. The fossils found in Namibia are well preserved and show creatures of both kinds. Trace fossils include those of burrows of the type that is generally interpreted as formed by sea anemones. These animals are passive predators and Ediacarans may have been their prey.
There’s no evidence that animals caused the extinction of Ediacarans eating them all. Animal of that time such as Waptia fieldensis may have preyed on the Ediacarans or at least might have become their competitors in the search for food. From this point of view, the evolution of animals may have been too quick for Ediacarans.
The period in which Ediacarans became extinct coincides with what is called the Cambrian explosion, a period of about 25 million years when most groups of animals existing today emerged. These animals adapted to quickly changing conditions, better than Ediacarans, and they ended up influencing their environment.
For quite some time Simon Darroch has been looking for evidence that animals caused the extinction of Ediacarans. In September 2015 he and his collaborators published a paper on this subject in the journal “Proceedings of the Royal Society B”, again mainly based on fossils found in Namibia.
This time his research focused on the fossils that show a mixed community of animals and Ediacarans. It may have been a transitional phase between a world where Ediacarans were widespread to one in which animals ousted them. According to Simon Darroch that extinction showed that the evolution of new behaviors can fundamentally change the entire planet. Something similar is happening today in a world in which human beings have the greatest influence on the environment.
