Monday, 7 September 2015

An Ecological Cause For The Ediacaran Extinction

The soft bodied, fractal world of the Ediacarans was
rendered extinct at the end of the Ediacaran period
The Ediacara biota represented the animal kingdom's first experiment in body building; a trial run for multicellularity. Some species possessed similar body plans to extant animals. Others were highly unusual, utilising fractal systems to construct tissues and organs.

The descendants of the Ediacarans who utilised symmetrical body plans exist today. The fractal system, however, was extinguished in a mass extinction event.

Mass extinctions had occurred before, such as during the oxygenation of the atmosphere or the glaciations which wracked the Precambrian Earth, but the Ediacaran extinction is the earliest known mass animal extinction.

Various causes have been put forward, including a decline in oxygen levels and the ecological changes associated with the Cambrian Explosion. Evidence to support the different causes was shaky, but a recent study shows that ecological changes were definitely a strong driving force behind the Ediacaran extinction.

'People have been slow to recognize that biological organisms can also drive mass extinction,' said Simon Darroch from Vanderbilt University. 'But our comparative study of several communities of Ediacarans, the world's first multicellular organisms, strongly supports the hypothesis that it was the appearance of complex animals capable of altering their environments, which we define as 'ecosystem engineers,' that resulted in the Ediacarans' disappearance.

An Ediacaran from the Farm Swartpunt site in Namibia
Darroch and his team conducted extensive palaeoecological and geochemical analyses on Ediacaran-bearing sites of different ages. The youngest, Farm Swartpunt in Namibia, is 545 million years old, giving insight into the last couple of million years of the Ediacaran period when Ediacaran faunas were in decline.

The other three, Mistaken Point in Newfoundland, Nilpena in South Australia and the White Sea in Russia, are 579 to 565 million, 555 to 550 million and 555 to 550 million years old respectively; these provide insight into a time when the Ediacaran faunas were flourishing.

'We found that the diversity of species at this site [Swartpunt] was much lower, and there was evidence of greater ecological stress, than at comparable sites that are 10 million to 15 million years older,' reported Darroch.

The Swartpunt site also preserved an increasing diversity of burrows and tracks made by the earliest complex animals, presenting a plausible link between the evolution and extinction of the Ediacarans. 'There is a powerful analogy between the Earth's first mass extinction and what is happening today,' concluded Darroch. 'The end-Ediacaran extinction shows that the evolution of new behaviours can fundamentally change the entire planet, and we are the most powerful 'ecosystem engineers' ever known.'