Toothy grin com­pletes pre­his­toric worm

The China Post - - FEATURE - BY MA­RI­ETTE LE ROUX

For decades, sci­en­tists have been try­ing to piece to­gether the anatomy of a tiny pre­his­toric worm so weird-look­ing that they named it Hal­lu­ci­ge­nia.

The stiff spikes on the longex­tinct crit­ter’s back were long thought to be legs, while seven pairs of spindly limbs were mis­taken for ten­ta­cles.

On Wed­nes­day a re­search duo said the crea­ture had not only been re­con­structed up­side down, but also back to front — they found a pair of eyes and a toothy mouth in what was long thought to be its back­side.

“Prior to our study, a large bal­loon-like orb at one end of the spec­i­men had been in­ter­preted as an amor­phous head,” said Martin Smith of the Univer­sity of Cam­bridge, who co-au­thored a study pub­lished in the jour­nal Na­ture.

“We can now demon­strate that this ac­tu­ally wasn’t part of the body at all but a dark stain rep­re­sent­ing de­cay flu­ids or gut con­tents that oozed out of the anus as the an­i­mal was com­pressed dur­ing burial,” he told AFP by email.

Smith and col­league JeanBernard Caron of the Univer­sity of Toronto, used an elec­tron mi­cro­scope to an­a­lyze dozens of Hal­lu­ci­ge­nia fos­sils in mu­seum col­lec­tions, and un­cov­ered “as­tound­ing new de­tail” of the worm that lived on the sea floor some 505-515 mil­lion years ago.

Af­ter iden­ti­fy­ing the worm’s der­riere, they de­cided to take a closer look at the other end — re­mov­ing the sed­i­ment cov­er­ing sev­eral of the fos­silized heads.

“When we put the fos­sils in the elec­tron mi­cro­scope, we were ini­tially hop­ing that we might find eyes,” said Smith.

“We were as­ton­ished when we found not just a pair of eyes, but also a cheeky grin — a set of teeth smil­ing back at us!”

Evo­lu­tion­ary Clue

The team’s anal­y­sis showed that Hal­lu­ci­ge­nia’s mouth was sur­rounded by a ring of spiny teeth, prob­a­bly used to suck up food, while the throat was lined with a row of nee­dle-like teeth which pos­si­bly pre­vented its lunch slip­ping back out.

At a mere one to five cen­time­ters ( 0.4 to two inches) long, the ar­mored worm lived dur­ing a pe­riod of Earth’s history called the Cam­brian Ex­plo­sion, when most ma­jor an­i­mal groups emerged.

First iden­ti­fied in the 1970s, Hal­lu­ci­ge­nia’s clos­est liv­ing rel­a­tive is the tooth­less vel­vet worm, which in turn be­longs to a vast fam­ily known as ecdyso­zoa — an­i­mals like many in­sects and worms, lob­sters and spi­ders which shed their ex­oskele­ton.

Hal­lu­ci­ge­nia’s newly dis­cov­ered chop­pers have led Smith and Caron to con­clude that the an­ces­tor of ecdyso­zoa must also have had a toothy mouth and throat.

“If so, this is very ex­cit­ing as it helps us to con­strain the tim­ing of the ori­gin of the group,” said Smith.

It seemed to in­di­cate that all ecdyso­zoan sub-groups split off “within a ge­o­log­i­cally brief 20 mil­lion per pe­riod of rapid evo­lu­tion, pro­vid­ing ev­i­dence for a rapid ‘Cam­brian Ex­plo­sion,’” he said.

A re­con­struc­tion of Hal­lu­ci­ge­nia’s walk­ing gait can be seen here: https:// youtu. be/ Gny9SxByOw8

AFP

This hand­out pic­ture re­leased by Na­ture, Univer­sity of Cam­bridge on Wed­nes­day, June 24 shows the fos­sil of a pre­his­toric worm, the Hal­lu­ci­ge­nia sparsa, from the Burgess Shale, mea­sur­ing 15 mm in length.

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