Cambrian Explosion: not from Ediacarans (Introduction)

by David Turell @, Wednesday, April 29, 2015, 15:17 (1803 days ago) @ David Turell

Tis article tries to explore the junction between Ediacarans and the Cambrian animals. A vast difference in development from sluggish to active. Still no intermediate forms that Darwin hoped for:

"Strange and largely immobile organisms made of tubes were the first complex life on Earth. Appearing 579 million years ago, they thrived on the seafloor for some 37 million years, then vanished - becoming a curiosity we know only from faint impressions in the sandstone fossil record.

"What made them die out? New fossil evidence from Namibia suggests that the Ediacarans, as these creatures are known, had their world turned upside by an explosion of life forms at the beginning of the Cambrian period 541 million years ago. Some of these may have evolved to eat their enigmatic predecessors and to bioengineer the environment in ways that left little hope for the passive Ediacarans.

"If so, the very first mass extinction of complex life forms had a biological cause, unlike the big five mass extinctions which are thought to be environmentally driven - kicked off by widespread volcanic eruptions that poisoned the oceans or a massive meteorite strike, for example.

"The disappearance of the Ediacarans from the fossil record has long troubled biologists. Leading theories are a catastrophic mass extinction, that Ediacarans got eaten or had their habitat destroyed by newly evolved animals, or no longer left fossils because of a change in ocean conditions.

"But a careful search by Marc Laflamme of the University of Toronto in Mississauga and colleagues threw up no geochemical signatures of low-oxygen conditions or other turmoil to support the idea of an environmentally driven mass extinction. And given that soft-bodied Cambrian animals are fossilised within rocks like the famed Burgess Shale, it seems unlikely that the conditions simply didn't allow any surviving Edicaranas to leave a fossil trace in the Cambrian period.

"That suggests that by the time the Cambrian explosion of species reached full force, the Ediacarans were gone,"

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