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Mystery fossils seem to represent tiny balls of cells

Sept. 25, 2014
Courtesy of Nature
and World Science staff

New­found fos­sils of strange, ti­ny ball-like crea­tures from around 600 mil­lion years ago are re­ported in the re­search jour­nal Na­ture this week. 

Un­der­stand­ing crea­tures from this early time has been dif­fi­cult as they are very dif­fer­ent from an­y­thing alive to­day. The new­found fos­sils are no ex­cep­tion. They seem to rep­re­sent a line­age that be­came an ev­o­lu­tion­ary dead end—they are not an­ces­tors of liv­ing an­i­mals, ac­cord­ing to the au­thors of the new stu­dy.

A Megaclonophycus fossil. The dark oval-shaped struc­ture is a sort of intern­al growth of un­clear function, called a Ma­tri­yosh­ka or rus­sian doll. (Cour­tesy Na­ture)


The fos­sils, from an area in south­ern Chi­na called the Edi­a­ca­ran Dou­shan­tuo Forma­t­ion, date back to just be­fore a burst of an­i­mal di­vers­ity known as the Cam­bri­an ex­plo­sion, ac­cord­ing to the re­search­ers. Life had not yet emerged from the oceans. Yet this “pre-Cam­bri­an era,” with hard-to-find fos­sils, rep­re­sents al­most 90 per­cent of the his­to­ry of life on Earth.

The new spec­i­mens, slightly under a mil­li­me­ter wide, are thought to offer a win­dow on­to the early ev­o­lu­tion of com­plex mul­ti­ple-celled or­gan­isms. 

Many fos­sils from the re­gion in Chi­na seem de­fy at­tempts to cat­e­go­rize them. For ex­am­ple, Mega­sphaera—an­other ball-like mi­cro­fos­sil made up of one or more cells in a thick en­velope—has been thought to rep­re­sent var­i­ous groups, in­clud­ing bac­te­ria, al­gae or early an­i­mal em­bryos.

The new “microfos­sils” from the Dou­shan­tuo Forma­t­ion show clear signs of traits char­ac­ter­is­tic of an­i­mals, said the au­thors, Shu­hai Xiao of Vir­gin­ia Tech uni­vers­ity and col­leagues. These char­ac­ter­is­tics in­clude cell dif­fer­entia­t­ion; separa­t­ion of re­pro­duc­tive cells; and “pro­grammed” cell death, a sys­tem used to clear out no-longer-useful cells. 

The ev­i­dence in­di­cates the fos­sils, dubbed Mega­clo­no­phy­cus, probably aren’t bac­te­ria, the au­thors said, call­ing for fur­ther in­ves­ti­ga­t­ion in­to where the mi­nus­cule crea­tures sit on the “family tree” of life.

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