Media Releases

Burgess shale worm provides crucial missing link

March 13, 2013

Discovery pushes fossil record back 200 million years

TORONTO, ON — Canada’s 505 mil­lion year-old Burgess Shale fos­sil beds, locat­ed in Yoho Nation­al Park, have yield­ed yet anoth­er major sci­en­tif­ic dis­cov­ery – this time with the unearthing of a strange phal­lus-shaped crea­ture.

A study to be pub­lished online in the jour­nal Nature on March 13 con­firms Spar­to­branchus tenuis is a mem­ber of the acorn worms group which are sel­dom-seen ani­mals that thrive today in the fine sands and mud of shal­low and deep­er waters.  Acorn worms are them­selves part of the hemi­chor­dates, a group of marine ani­mals close­ly relat­ed to today’s sea stars and sea urchins.

“Unlike ani­mals with teeth and bones, these spaghet­ti-shaped crea­tures were soft-bod­ied, so the fos­sil record for them is extreme­ly scarce,” said lead author Dr. Jean-Bernard Caron, asso­ciate pro­fes­sor of earth sci­ences and ecol­o­gy & evo­lu­tion­ary biol­o­gy at the Uni­ver­si­ty of Toron­to and cura­tor of inver­te­brate palaeon­tol­ogy at the Roy­al Ontario Muse­um. “Our analy­sis of Spar­to­branchus tenuis, a crea­ture pre­vi­ous­ly unknown to sci­ence, push­es the fos­sil record of the enterop­neusts back by 200 mil­lion years and fun­da­men­tal­ly changes our under­stand­ing of evo­lu­tion from this peri­od.”

Since their dis­cov­ery in the 19th-cen­tu­ry, some of the biggest ques­tions in hemi­chor­date evo­lu­tion have focused on the group’s ori­gins and the rela­tion­ship between its two main branch­es: the enterop­neusts and pter­o­branchs. Enterop­neusts and pter­o­branchs look very dif­fer­ent, yet share many genet­ic and devel­op­men­tal char­ac­ter­is­tics that reveal an oth­er­wise unex­pect­ed close rela­tion­ship.

Spar­to­branchus tenuis rep­re­sents a cru­cial miss­ing link that serves not only to con­nect the two main hemi­chor­date groups but helps to explain how an impor­tant evo­lu­tion­ary trans­for­ma­tion was achieved,” added Caron. “Our study sug­gests that prim­i­tive enterop­neusts devel­oped a tubu­lar struc­ture – the smok­ing gun – which has been retained over time in mod­ern pter­o­branchs.”

Hemi­chor­dates also share many of the same char­ac­ter­is­tics as chor­dates – a group of ani­mals that includes humans – with the name hemi­chor­date rough­ly trans­lat­ing to ‘half a chor­date.’

Spar­to­branchus tenuis prob­a­bly fed on small par­ti­cles of mat­ter at the bot­tom of the oceans. “There are lit­er­al­ly thou­sands of spec­i­mens at the Wal­cott Quar­ry in Yoho Nation­al Park, so it’s pos­si­ble Spar­to­branchus tenuis may have played an impor­tant role in recy­cling organ­ic mat­ter in the ear­ly Burgess Shale envi­ron­ment, sim­i­lar to the eco­log­i­cal ser­vice pro­vid­ed by earth worms today on land,” said Caron.

Detailed analy­sis sug­gests Spar­to­branchus tenuis had a flex­i­ble body con­sist­ing of a short pro­boscis, col­lar and nar­row elon­gate trunk ter­mi­nat­ing in a bul­bous struc­ture, which may have served as an anchor. The largest com­plete spec­i­mens exam­ined were 10 cen­time­tres long with the pro­boscis account­ing for about half a cen­time­tre. A large pro­por­tion of these worms was pre­served in tubes, of which some were branched, sug­gest­ing the tubes were used as a dwelling struc­ture.

Oth­er mem­bers of the Spar­to­branchus tenuis research team are Simon Con­way Mor­ris of the Uni­ver­si­ty of Cam­bridge and Christo­pher B. Cameron of the Uni­ver­sité de Mon­tréal. Last year Con­way Mor­ris and Caron pub­lished a well-pub­li­cized study on Pika­ia, believed to be one of the planet’s first human rel­a­tives.

The Burgess Shale is found in Yoho Nation­al Park, part of the Cana­di­an Rocky Moun­tain Parks World Her­itage Site, and is one of the most impor­tant fos­sil deposits for under­stand­ing the ori­gin and ear­ly evo­lu­tion of ani­mals that took place dur­ing the Cam­bri­an Explo­sion start­ing about 542 mil­lion years ago. To learn more about the Burgess Shale vis­it:

The study, enti­tled Tubi­colous enterop­neusts from the Cam­bri­an peri­od, is avail­able at as of March 13 at 2 pm.

***NOTE: Visu­als are at***



Jean-Bernard Caron
Uni­ver­si­ty of Toron­to
416 586 5593 ext. #1

Christo­pher Cameron
Uni­ver­sité de Mon­tréal
514 343 2198
416 946 5499

Omar McDa­di
Parks Cana­da
403 522 1277
403 760 1090 (cell)

Simon Con­way Mor­ris
Uni­ver­si­ty of Cam­bridge
44 (0) 1223 333414/333400

David McK­ay
Roy­al Ontario Muse­um
416 586 5559

Chris­tine Elias
Com­mu­ni­ca­tions, Fac­ul­ty of Arts & Sci­ence
Uni­ver­si­ty of Toron­to
416 946 5499