Media Releases

Human’s oldest ancestor found in Burgess Shale

March 5, 2012

Researchers from the Uni­ver­si­ty of Toron­to, the Roy­al Ontario Muse­um (ROM) and the Uni­ver­si­ty of Cam­bridge have con­firmed that a 505 mil­lion-year-old crea­ture, found only in the Burgess Shale fos­sil beds in Canada’s Yoho Nation­al Park, is the most prim­i­tive known ver­te­brate and there­fore the ances­tor of all descen­dant ver­te­brates, includ­ing humans.

The research team’s analy­sis proves the extinct Pika­ia gracilens is the most prim­i­tive mem­ber of the chor­date fam­i­ly, the group of ani­mals that today includes fish, amphib­ians, birds, rep­tiles and mam­mals. Their study is based on the analy­sis of 114 spec­i­mens and will be pub­lished in the British sci­en­tif­ic jour­nal Bio­log­i­cal Reviews on March 5.

Pika­ia was first described, on the basis of only a few spec­i­mens, by Amer­i­can palaeon­tol­o­gist Charles Doolit­tle Wal­cott in 1911 as a pos­si­ble annelid worm, a group that includes today’s leech­es and earth­worms. How­ev­er, sci­en­tists have long spec­u­lat­ed that Pika­ia was a chor­date because it appeared to have a very prim­i­tive noto­chord – a flex­i­ble rod found in the embryos of all chor­dates – which goes on to make up part of the back­bone in ver­te­brates.

“Our analy­sis pro­vides evi­dence that Pika­ia indeed had a noto­chord,” said co-author of the study Jean-Bernard Caron, an assis­tant pro­fes­sor of ecol­o­gy and evo­lu­tion­ary biol­o­gy at U of T and cura­tor of inver­te­brate palaeon­tol­ogy at the ROM. A nerve cord and vas­cu­lar sys­tem were also iden­ti­fied in their study.  “But the real excite­ment was find­ing exten­sive myomeres, the blocks of skele­tal mus­cle tis­sue that are char­ac­ter­is­tic of chor­dates.”

“The dis­cov­ery of myomeres is the smok­ing gun that we have long been seek­ing,” said the study’s lead author, Pro­fes­sor Simon Con­way Mor­ris of the Uni­ver­si­ty of Cam­bridge. “Now with  myomeres, a nerve chord, a noto­chord and a vas­cu­lar sys­tem all iden­ti­fied, this study clear­ly places Pika­ia as the planet’s most prim­i­tive chor­date. So, next time we put the fam­i­ly pho­to­graph on the man­tle-piece, there in the back­ground will be Pika­ia.”

Aver­ag­ing about five cen­time­tres in length, Pika­ia was a side­ways-flat­tened, some­what eel-like ani­mal. The flat­tened body is divid­ed into a series of seg­ment­ed mus­cle blocks seen as S‑shaped lines that lie on either side of the noto­chord which runs along most if not all of the body length. It like­ly swam above the sea by mov­ing its body in a series of side-to-side curves.

The Burgess Shale is famous for its weird and won­der­ful fos­sils of marine organ­isms. The site pro­vides vital infor­ma­tion about evo­lu­tion dur­ing the Cam­bri­an explo­sion, a peri­od over half a bil­lion years ago that was char­ac­ter­ized by the appear­ance of a vast diver­si­ty of ani­mals over a short peri­od of time.

The study exam­ined 114 Pika­ia fos­sils using a range of imagery tech­niques, includ­ing scan­ning elec­tron microscopy, to reveal fine details. The bulk of the spec­i­mens are held in trust for Parks Cana­da at the ROM while near­ly all the remain­der are housed in the Nation­al Muse­um of Nat­ur­al His­to­ry, part of the Smith­son­ian Insti­tu­tion in Wash­ing­ton, DC.

“It’s very hum­bling to know that swans, snakes, bears, zebras and, incred­i­bly, humans all share a deep his­to­ry with this tiny crea­ture no longer than my thumb,” said Caron.

“Fos­sils of prim­i­tive chor­dates are incred­i­bly rare. With no back­bones or oth­er min­er­al­ized ele­ments, Pika­ia would stand no chance of preser­va­tion in nor­mal con­di­tions out­side excep­tion­al sites like the Burgess Shale. We hope that, with con­tin­u­ing explo­rations and field work stud­ies there, oth­er species will be dis­cov­ered allow­ing us to refine our under­stand­ing of the ear­ly his­to­ry of our own group.”

The con­fir­ma­tion of Pika­ia as a chor­date is the lat­est in a recent string of Burgess Shale dis­cov­er­ies. In Novem­ber 2011, evi­dence of fos­silized tracks of a large preda­tor known as Tegopelte were pub­lished, and in Jan­u­ary 2012 a bizarre tulip-shaped crea­ture named Siphusauc­tum was described for the very first time.

Man­aged by Parks Cana­da in Yoho Nation­al Park, the Burgess Shale was rec­og­nized in 1981 as one of Canada’s first UNESCO World Her­itage Sites. It is now pro­tect­ed under the larg­er Rocky Moun­tain Parks UNESCO World Her­itage Site. To learn more about the Burgess Shale vis­it:



For more infor­ma­tion, please con­tact:

Jean-Bernard Caron
Ecol­o­gy & Evo­lu­tion­ary Biol­o­gy and Geol­o­gy
Uni­ver­si­ty of Toron­to and Cura­tor, Inver­te­brate Palaeon­tol­ogy
Roy­al Ontario Muse­um

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

Kim Luke
Com­mu­ni­ca­tions, Fac­ul­ty of Arts & Sci­ence
Uni­ver­si­ty of Toron­to