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Oldest complex organic molecules found in fossils

Oct. 25, 2006
By Pam Frost Gorder/Ohio State University 
and World Science staff

Ge­ol­o­gists say they’ve found com­plex or­gan­ic mo­le­cules, char­ac­ter­is­tic com­po­nents of liv­ing things, in 350-mil­lion-year-old fos­sil sea crea­tures—the old­est such mo­le­cules yet found. These of­fer a new way to map ev­o­lu­tion, the re­search­ers said.

A modern crinoid, also known as a sea lily. (Courtesy NOAA)


The molecules, they added, are ones that to­day serve as or­ange and yel­low pig­ments in re­lat­ed an­i­mals, and thus might have done the same back then.

Chris­ti­na O’­Mal­ley, a doc­tor­al stu­dent in earth sci­en­ces at Ohio State Uni­ver­si­ty in Co­lum­bus, Ohio, re­por­t­ed find­ing the bunch­es of at­oms in fos­sils of sev­er­al spe­cies of sea crea­tures called cri­noids. 

She re­ported the re­search Wed­nes­day at the meet­ing of the Ge­o­log­i­cal So­ci­e­ty of Amer­i­ca in Phi­l­a­del­phia.

Crinoids, also known as sea li­lies, still ex­ist. They re­sem­ble plants, but are an­i­mals. They cling to the sea
­floor and eat plank­ton, mass­es of ti­ny plant and an­i­mal or­ga­n­isms that drift by. 

The cri­noids in this study had flower-like fronds cap­ping skin­ny stalks about six inches (15 cm) high—a look re­sem­b
­ling “star­fish on a stick,” said Wil­liam Au­sich, an earth sci­ences pro­fes­sor and O’­Mal­ley’s co-advisor at Ohio State.

Crinoids to­day dis­play var­ied col­ors, in­clud­ing shades of red, or­ange, and yel­low, so it would make sense that si­m­i­lar co­lors turned up in their fore­bears, Au­sich said.

It’s not the first time that ancient or­gan­ic mo­le­cules from fos­sils have been re­ported, O’Mal­ley said. But to her knowl­edge, she added, these are the old­est, and also the first that can be linked to in­di­v­i­du­al spe­cies.

Fos­sils of cri­noids from 350 mil­lion years ago. (Cour­te­sy OSU)


Be­cause the mo­le­cules seem to be slight­ly dif­fer­ent for each cri­noid spe­cies, sci­en­tists can use them as mar­k­ers to map re­la­tion­ships on the crea­tures’ fa­m­i­ly tree, the re­search­ers said. Un­til now, they could on­ly in­fer cri­noid li­n­e­age based on the size and shape of key ske­le­tal fea­tures.

“We can look for clues about these crea­tures’ lives in a way that has­n’t been at­temp­t­ed,” O’­Mal­ley said.

Sci­en­t­ists can nor­m­al­ly view fos­si­lized plants and an­i­mals on­ly in the grays and tans of se­d­i­men­t­a­ry rock, such as the lime­stone fos­sils in this stu­dy. Rock nor­mal­ly re­places or­ga­n­ic mo­l­e­cules dur­ing fos­si­l­i­z­a­tion. But “cri­noid ske­l­e­ton is very por­ous,” she said, so ap­pa­rent­ly some or­gan­ic mo­l­e­cules were trapped in it and sur­vived fos­si­l­i­za­tion.

O’­Mal­ley said she found pig­ments in every cri­noid spec­i­men sam­pled from three fos­sil sites, one in Switz­er­land and two in In­di­an­a.

The In­di­an­a sam­ples date back 350 mil­lion years, the sci­en­tists said, to the so-called Mis­sis­sip­pi­an pe­ri­od, when much of North Amer­i­ca was un­der a shal­low in­land sea. The Switz­er­land fos­sils were dat­ed to 60 mil­lion years ago, the Ju­ras­sic pe­ri­od. The sites pre­served the cri­noids ex­cep­tion­al­ly well, they added, prob­a­bly be­cause a sud­den storm bur­ied them in sed­i­ment.

Should pig­ments be found in oth­er fos­sils, the tech­nique could prove a re­li­a­ble way to trace spe­cies’ ev­o­lu­tion, the re­search­ers con­tin­ued. So far, the cri­noid “biomark­ers” mesh well with cur­rent con­cepts of how those spe­cies are re­lat­ed, they said.

Or­gan­ic mo­le­cules might al­so sur­vive in fos­sils of oth­er types of an­i­mals, but it’s not clear wheth­er it would be as easy to ex­t­ract them, nor wheth­er the same meth­ods would be suit­a­ble, O’­Mal­ley said. “Very few stud­ies have looked for com­plex or­gan­ic mo­le­cules in fos­sil­s,” she wrote in an e­mail.

O’­Mal­ley iso­lat­ed molecules by grind­ing up and dis­solv­ing tiny bits of fos­sil, then in­ject­ing some of the re­sult­ing so­lu­tion in­to a ma­chine called a gas chro­ma­to­graph mass spec­trom­e­ter. This va­por­ized the so­lu­tion so that a mag­net could sep­a­rate mo­le­cules by elec­tric charge and mass. Com­put­er soft­ware then iden­ti­fied them.


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Geologists say they have found the oldest complex organic molecules, characteristic components of living things, in 350-million-year-old fossil sea creatures. The ancient molecules contain information that offers a totally new way map evolution, the researchers said. The molecules in this case, they added, are ones that today function as orange and yellow pigments in related animals, so they might have served the same purpose back then. Christina O’Malley, a doctoral student in earth sciences at Ohio State University in Columbus, Ohio, found the molecules in fossils of several species of sea creatures known as crinoids. She reported the research Wednesday at the meeting of the Geological Society of America in Philadelphia. Crinoids still exist. They resemble plants, but are animals. They cling to the seafloor and eat plankton, masses of tiny plant and animal organisms, drifting by. The crinoids in this study had flower-like fronds capping skinny stalks about six inches (15 cm) high—a look resembling “starfish on a stick,” said William Ausich, an earth sciences professor and O’Malley’s co-advisor at Ohio State. Crinoids today display varied colors, including shades of red, orange, and yellow, so it makes sense that similar turned up in their forebears, Ausich said. “People have suspected for a long time that organic molecules could be found inside fossils,” he added. “This is just the first time that scientists have succeeded in finding them.” Because the molecules seem to be slightly different for each crinoid species, scientists can now use the pigments as markers to map relationships on the creatures’ family tree, the researchers said. Until now, they could only infer crinoid lineage based on the size and shape of key features on the animals’ skeletons. “We can look for clues about these creature’s lives in a way that hasn’t been attempted,” O’Malley said. Scientists can normally view fossilized plants and animals only in the grays and tans of sedimentary rock, such as the limestone fossils in this study. Rock is inorganic, and replaces organic molecules during fossilization. What O’Malley and her colleagues found is that some organic molecules occasionally survive. “Crinoid skeleton is very porous,” she said. “We think that when inorganic molecules filled in the spaces of the skeleton during preservation, some of the organic molecules were trapped inside the fossil.” O’Malley said she found pigments in every crinoid specimen sampled from three fossil sites, one in Switzerland and two in Indiana. The Indiana samples date back to 350 million years ago, the scientists said, during the so-called Mississippian period, when much of North America was under a shallow inland sea. The Switzerland fossils were dated back 60 million years, to the Jurassic period. The sites preserved the crinoids exceptionally well, they added, probably because a sudden storm buried them in sediment. Should pigments be found in other fossils, the technique could prove a reliable way to trace species’ evolution, the researchers continued. So far, the crinoid “biomarkers” mesh well with scientists’ concepts of how those species are related, they said. O’Malley isolated pigments by grinding up bits of fossil, dissolving the organic molecules and injecting a sample of the resulting solution into a machine called a gas chromatograph mass spectrometer. This vaporized the solution so that a magnet could separate molecules by their electric charge and mass. Computer software then identified them.