Time run­ning out on solv­ing China’s fos­sil mys­tery

Are spec­i­mens threat­ened by min­ing the old­est an­i­mal rem­nants?

The Washington Post Sunday - - THE WORLD - BY BEN GUARINO ben.guarino@wash­post.com

The rocks of the Doushan­tuo For­ma­tion, in China’s Guizhou Prov­ince, are sprin­kled with tiny, an­cient fos­sils. They are no more than a mil­lime­ter in length. The 600-mil­lion-yearold or­gan­isms are pre­served with such de­tail that the fos­sils, when freed from the rock in a chem­i­cal bath and scanned with X-rays, re­veal not only in­di­vid­ual cells but pos­si­ble cell nu­clei. Some fos­sils are jagged and round, like wiz­ened Koosh balls. Other orbs, among the most in­trigu­ing spec­i­mens, are split by Y-shaped seams.

When viewed from the side, the cel­lu­lar clus­ters look a bit like pie sliced in thirds. When viewed by bi­ol­o­gists, the clus­ters also look a bit like an­i­mal em­bryos, frozen in time.

“If they are an­i­mals, they’d be the old­est an­i­mals in the fos­sil records,” said John Cun­ning­ham, a pa­le­o­bi­ol­o­gist at the Univer­sity of Bris­tol in Bri­tain.

Cun­ning­ham is not con­vinced that the or­gan­isms, known as the Weng’an biota, are in­deed an­cient an­i­mals.

In a re­port pub­lished Wed­nes­day in the Jour­nal of the Ge­o­log­i­cal So­ci­ety, Cun­ning­ham and his co-au­thors ex­am­ined the best ev­i­dence for and against the case that the fos­sils are from an­i­mals. Their an­swer is: They don’t know.

An­cient trilo­bites and other scat­tered spec­i­mens pro­vide con­vinc­ing ev­i­dence that an­i­mals lived 530 mil­lion years ago.

Given what sci­en­tists know about the rate at which or­gan­isms branch off from com­mon an­ces­tors, the first an­i­mals should ap­pear in the fos­sil record about 70 mil­lion years or so be­fore those crea­tures — right around the time of the Weng’an biota.

Tim­ing alone, though, isn’t suf­fi­cient ev­i­dence. Nor are the Y-shaped seams. Al­gae cells also grow Y junc­tions, noted the au­thors of the new re­port.

“It seems that none of the char­ac­ter­is­tics which have been used are unique to any kind of an­i­mals,” Cun­ning­ham said.

“This is a good study that sum­ma­rizes the cur­rent ‘state of the art’ on Weng’an fos­sils,” said David Bot­tjer, a pa­le­on­tol­o­gist at the Univer­sity of South­ern Cal­i­for­nia who has been study­ing the re­gion’s fos­sils since 1998.

When pa­le­on­tol­o­gists first de­scribed the fos­sils in the late 1990s, they sug­gested that the Weng’an biota were an­i­mals.

“It is fair to say that this has been dis­puted since then, as no ‘smok­ing gun’ for an­i­mal fos­sils has emerged,” said Bot­tjer, who was not in­volved with the new pa­per.

Shuhai Xiao, a pro­fes­sor of pa­le­o­bi­ol­ogy at Vir­ginia Tech who was among the first wave of re­searchers to study the Weng’an biota, ex­pressed doubt about the al­gae ex­pla­na­tion.

There’s no good ev­i­dence that th­ese fos­sils are pho­to­syn­thetic, Xiao said, in the way that al­gae are.

Though some species of al­gae grow in balls, th­ese clumps are hol­low; cells caught in the cen­ter wouldn't get enough sun­light to sur­vive.

The clus­ters of Weng’an biota are solid, full of cells.

Xiao main­tains that an an­i­mal ori­gin, though not def­i­nite, is more likely than the new pa­per sug­gests.

“But I think that’s okay,” Xiao said. “It’s hard to in­ter­pret things that are more than half a bil­lion years old.”

While sci­en­tists de­bate if the fos­sils are em­bryos, the spec­i­mens face a threat worse than un­cer­tain tax­on­omy: bull­doz­ers.

Twenty years ago, when Xiao was a grad­u­ate stu­dent, the land around the Doushan­tuo For­ma­tion was green and beau­ti­ful. Xiao re­turned two years ago to col­lect more sam­ples. “Now it’s very ugly,” he said, turned gray by trucks and quarry ma­chin­ery. The site is rich not just in fos­sils but also in phos­phate, used as raw ma­te­rial to pro­duce fer­til­izer.

Xiao said that the min­ing op­er­a­tion had al­ready de­stroyed the above­ground out­crop­pings.

To find a con­tin­u­ous sec­tion of rock from which to col­lect sam­ples, he re­lied in­stead on the walls of min­ing tunnels.

But be­cause the tun­nel net­work risks col­lapse, the min­ers plan to fill the holes with loose rock, he said, also seal­ing away the fos­sils.

“They’re be­ing quar­ried at a really mas­sive rate,” Cun­ning­ham said.

“If they’re all quar­ried out it would be very sad. The chance to find more fos­sils from this de­posit would be lost.”

Chi­nese pa­le­on­tol­o­gists and others around the world have pe­ti­tioned the Chi­nese govern­ment to curb the min­ing op­er­a­tion, though one re­searcher told Sci­ence mag­a­zine in April that a third of the fos­sil sites are al­ready gone.

By us­ing ad­vanced tech­niques like syn­chro­tron X-ray ma­chines — akin to med­i­cal CT scan­ner, but meant for much smaller tar­gets — sci­en­tists can wring more in­for­ma­tion from fos­sils al­ready col­lected.

But there re­mains one ques­tion best an­swered by a con­tin­ued hunt: If th­ese are in­deed an­i­mal em­bryos, might adults ex­ist in the de­posit?

The an­swer, again, is am­bigu­ous. Per­haps the eggs sank to the bot­tom of the ocean, where con­di­tions fa­vored their fos­siliza­tion over the preser­va­tion of squishy, free-swim­ming adults.

But sci­en­tists like Xiao are op­ti­mistic that there are new dis­cov­er­ies wait­ing in the rocks.

“De­spite its im­por­tance, there have been rel­a­tively few stud­ies of the Weng’an biota,” Bot­tjer said.

“So, there is ev­ery rea­son to think that fu­ture stud­ies will turn up ad­di­tional ev­i­dence for the ex­is­tence of an­i­mal life, in­clud­ing lar­vae and adult spec­i­mens.”

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