No Single Factor Behind Cambrian Explosion Of Animal Life
September 20, 2013

No Single Factor Behind Cambrian Explosion Of Animal Life

April Flowers for - Your Universe Online

A new study from the UK reveals that the explosion of animal life on Earth that occurred around 520 million years ago was the result of a combination of interlinked factors, rather than a single underlying cause.

Over the past few decades, dozens of individual theories have been put forth for the rapid diversification of animal species in the early Cambrian period. The new study, published in Science, suggests a more holistic approach is required to discover the reasons behind what has become known as the Cambrian Explosion (CE).

Scientific theories for the CE fall into three main categories: geological, geochemical and biological. Most of these theories call for standalone processes as the main cause of the CE.

Regardless of the cause, the CE was a major evolutionary event that led to a wide range of biological innovation. This innovation included the origin of modern ecosystems, a rapid increase in animal diversity, the origin of skeletons and the first appearance of specialist modes of life such as burrowing and swimming.

There were many weird and wonderful creatures that emerged during the early Cambrian, including Anomalocaris -- the free-swimming, three foot-long top predator of the time with a mouth composed of 32 overlapping plates that could constrict and crush prey. The Anomalocaris is distantly related to modern arthropods, including crabs and lobsters.

Vertebrate animals also made their debut in the Cambrian Explosion. These are the distant ancestors of modern fish, reptiles, birds and mammals.

Professor Paul Smith of Oxford University along with Professor David Harper of Durham University and a team of scientists spent four years working on data collected in northernmost Greenland, at a site facing the Arctic Ocean.

Just 500 miles from the North Pole in a remote part of northern Greenland, Siriuspasset is located at 83°N and is logistically very difficult to reach. The team was attracted to the site because of the high quality of its fossil material and the insights it provides.

Professor Smith, Director of the Oxford University Museum of Natural History, said, "This is a period of time that has attracted a lot of attention because it is when animals appear very abruptly in the fossil record, and in great diversity. Out of this event came nearly all of the major groups of animals that we recognize today. Because it is such a major biological event, it has attracted much opinion and speculation about its cause."

The research team describes the CE as a "cascade of events." The interacting causes behind the explosion in animal life are likely to have begun with an early Cambrian sea-level rise, according to the team. This sea-level rise generated a large increase in the area of habitable seafloor, which in turn drove an increase in animal diversity. The cascading early events translated into the complex interaction of biological, geochemical and geological processes described in individual hypotheses.

Professor Harper, Professor of Palaeontology in the Department of Earth Sciences at Durham University, said, "The Cambrian Explosion is one of the most important events in the history of life on our planet, establishing animals as the most visible part of the planet's marine ecosystems."

"It would be naive to think that any one cause ignited this phenomenal explosion of animal life. Rather, a chain reaction involving a number of biological and geological drivers kicked into gear, escalating the planet's diversity during a relatively short interval of deep time," he added.

"The Cambrian Explosion set the scene for much of the subsequent marine life that built on cascading and nested feedback loops, linking the organisms and their environment, that first developed some 520 million years ago," said Harper.

Professor Smith added, "Work at the Siriuspasset site in north Greenland has cemented our thinking that it wasn't a matter of saying one hypothesis is right and one is wrong. Rather than focusing on one single cause, we should be looking at the interaction of a number of different mechanisms."

"Most of the hypotheses have at least a kernel of truth, but each is insufficient to have been the single cause of the Cambrian explosion. What we need to do now is focus on the sequence of interconnected events and the way they related to each other – the initial geological triggers that led to the geochemical effects, followed by a range of biological processes," he concluded.