Earliest human ancestor discovered

Posted by Emma Woollacott

British and canadian researchers have confirmed that a 505 million-year-old creature is the most primitive known vertebrate - and therefore the ancestor of us all.

Found only in the Burgess Shale fossil beds in Canada’s Yoho National Park, Pikaia gracilens has been confirmed as the most primitive member of the chordate family - the group of animals that today includes fish, amphibians, birds, reptiles and mammals.

Averaging about five centimetres in length, it was a sideways-flattened creature something like an eel, that likely swam above the sea floor by moving its body in a series of side-to-side curves.

And through an analysis of 114 Pikaia fossils using techniques including scanning electron microscopy, fine details have been revealed that settle the question of whether it was a chordate or not.

Back when it was discovered, in 1911, it was classified as a possible annelid worm, a group that includes today’s leeches and earthworms. But there's long been speculation that it was in fact a chordate.

It appeared to have a very primitive notochord – the flexible rod found in the embryos of all chordates, and which goes on to make up part of the backbone in vertebrates. 

Key was the discovery of myomeres, a type of skeletal muscle tissue found only in chordates.

"The discovery of myomeres is the smoking gun that we have long been seeking," says 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 mantlepiece, there in the background will be Pikaia."