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What if you had a theory you were positive was right, but there was always a fragment of missing evidence? Darwin had that problem.
Even the father of evolution was confounded by one thing. How could the Cambrian Explosion, which spawned most all of the animal groups whose descendants still exist today, have happened when there was barely any evidence of abundant life from before? So little was known about anything that lived before the Cambrian period because of the lack of soft tissues, which usually break down before they can be fossilized. Darwin’s Dilemma dragged on. Now an unusual pre-Cambrian creature with preserved soft tissue may have the answer.
“Exceptional preservation of fossils from the Ediacaran-Cambrian, ca. 570 to 500 million years ago, provides great insight into the first radiation of metazoans,” said Amy Shore, who led a study recently published in Science Advances.
Metazoans are animals, or, if you want to get really scientific, multicellular organisms which are also eukaryotic. Eukaryotic genes take the form of DNA found in the nuclei of their cells. Some of the weirdest metazoans to ever creep or crawl or float around on this planet came out of the Ediacaran.
547 million years ago, the bodies of some dead Namacalathus—which looked something like tiny pincushions on stalks—was buried in sediment. They lived and died during the Ediacaran period. Thought to be a transitional era for life on Earth, the Ediacaran was swarming with microorganisms before the Cambrian would bring on a drastic change. It was during this last preCambrian period that oxygen levels in the oceans rose high enough to support the more complex organisms which would eventually appear. Though the reasons for the oxygen boost have remained unclear, one of them might have been buried in carbon or pyrite.
Darwin swore that there Earth had to have a plethora of life-forms before the Cambrian Explosion, or there would have been no Cambrian Explosion. He was right.
When University of Edinburgh paleontologists on a dig in Namibia found Namacalathus fossils and examined them with X-ray imaging, it revealed that some of their soft tissues were impeccably preserved because they had been fossilized in pyrite (much like the Australian dinosaur bones found opalized in opal mines). The only fossils of Namacalathus that had been unearthed before were skeletal. What made relating Ediacaran life to Cambrian life even more difficult before the find was the assumption that organisms from each era were unrelated. These pyritized fossils were an unprecedented find that allowed the research team to find out which Cambrian metazoans they were related to, and even some extant fauna.
“Pyrite [must have] formed very early and replaced both soft tissue and the inferred organic-rich parts of the skeleton,” Shore said. “The occurrence of pyritized bacteria, here found alongside Namacalathus, is highly unusual in the fossil record and confirms that pyritization was rapid enough to replicate soft tissue.”
Cambrian life didn’t just materialize out of nowhere. It was during the Ediacaran, a period of dramatic environmental shifts, that the predecessors of those creatures emerged as some of the first more complex organisms on the planet. They had 40 million years to grow larger and began to diversify. When they vanished from the fossil record, it was right on the edge of what would become the most biologically diverse period the planet would see up until then.
Pyrite may be called fool’s gold, but something else that came out of this Ediacaran goldmine was proof that the life which had been thought to have shown up in the Cambrian period actually started to develop further back in time than previously thought. It was the elusive evidence that Darwin had been searching for.
Just imagine waiting over a century and a half for your theory to finally be proven right. Even as a ghost, you would be exhausted.