Timeline Of Animal Evolution Might Need To Be Rewritten, New Study Suggests

Trilobites were one of the animals that evolved during the Cambrian Explosion. Abrilla/Shutterstock

The most important event in the history of life on Earth is often considered to be the Cambrian Explosion. From about 541 to 516 million years ago, life began to diversify and by the end of this era, all major animal body plans had developed. This event changed the biosphere forever.

Now, an international team of researchers has published findings that suggest that the Cambrian Explosion was one of a series of events that led to the diversity of fauna we observe in the world today. These events stretch to at least 571 million years ago, during the Ediacaran period, a time that spans from about 635 to 541 million years.

The researchers studied fossils from the late Ediacaran and noticed an increase in diversity corresponding to specific changes in the environment. Around the planet, fluctuations in the amounts of oxygen and minerals available to lifeforms suggest that complex organisms might have developed at different times.

As reported in the journal Nature Ecology & Evolution, the team suggests that explosions of animal diversity started earlier, occurred over a longer period, and were more frequent than previously considered.

"Integrating data from the fossil record with that of environmental changes that affected the whole planet is revealing the patterns and drivers of the rise of complex life on Earth," study leader Professor Rachel Wood, of the University of Edinburgh's School of GeoSciences, said in a statement. "We used to think early animals emerged rapidly following a single evolutionary event, but our findings suggest it actually happened in stages." 

The team sees the Cambrian Explosion as a particularly crucial diversification event but not a unique one. They say it is part of a series, with some events happening before and others taking place after. The Cambrian Explosion certainly saw the rise of bilaterians, animals that possessed bilateral symmetry (our ancestors).

The causes of the Cambrian Explosion are not clear. Oxygen levels and the presence of minerals might be very important, but other researchers suggest that the formation of the ozone layer might be the dominant factor. Other suggestions include the development of eyes. The prey-predator relationship might also have been important, as it could have generated an arms race between species.

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