Frozen in time: roadworks yield fossil find

By Kristen Van Schie Time of article published Sep 3, 2013

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Johannesburg - About 360 million years ago, a scorpion fell into an estuary.

Parts of it were quickly covered in fine mud, cutting them off from oxygen – and decay.

They remained undisturbed for hundreds of millions of years.

But after years of roadworks and the patient detective work of a Wits University scientist, they are now the oldest land-living fossils found on what was once the Gondwana supercontinent.

The find was published last week in the journal African Invertebrates.

The scorpion, named Gondwanascorpio emzantsiensis, was discovered last year by Dr Robert Gess of Wits’s Evolutionary Studies Institute in pieces of shale from the Witpoort Formation in the Eastern Cape.

The shale was first uncovered in 1985 during construction of the N2 bypass outside Grahamstown. But the engineering was unstable: twice the formation had to be cut back to prevent avalanches – once in 1999 and again between 2007 and 2008.

Gess worked with Sanral to save blocks of shale.

The discovery took years.

“Palaeontology is not just a treasure hunt,” Gess said. “It’s a systematic study.”

And so, once or twice a week, he would chip through the layers of shale, methodically recording the rich record of fish and plant fossils.

And then, one day, he spotted scorpion pincers.

“I immediately realised it was something quite special,” he said.

Terrestrialisation began during the Silurian period – about 443 to 419 million years ago – when plants began moving from the waters onto land.

“Before that, all life as we know it was in the sea,” Gess said. The insects and millipedes followed, feeding on plants and debris.

And by the late Silurian period – about 360 million years ago – predatory invertebrates like the scorpion appeared. The first aquatic four-legged vertebrates had also arisen by then.

In time, they too would follow the invertebrates ashore and develop into all the bony land animals that are our ancestors.

But with their softer, leathery exoskeletons, scorpion fossils are rare finds.

All the specimens that had been found before were from Laurasia, the northern supercontinent that was made up of modern-day Europe, North America and Asia, or from China.

“From the late Devonian, only two other scorpion species have been found,” Gess said. “One was from China and the other from Canada.”

Nothing had been found from the southern continent of Gondwana, made up of Africa, South America, Australia and Antarctica.

Gess’s find now tells us what uncharted parts of the world looked like 360 million years ago.

At the time, what is now the Eastern Cape, where the fossil was found would have been just 15 degrees from the South Pole.

But, far from freezing, the conditions were likely more wooded, with plenty of insect life providing food for the scorpions.

“Before this, we only knew for certain that invertebrates were on land in Laurasia,” Gess said.

“Now we know for certain that not just scorpions, but whatever they were preying on, were also here,” he added. - The Star

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