A strange sea creature was anatomically unlike anything that had ever been seen; reversing it led to an epiphany

An extinct ribbon-like sea creature the size of a human hand was one of the first animals to develop a precursor to a backbone. Scientists recently identified the animal's nerve cord by using a reverse twist. They turned the fossils upside down.

Paleontologist Charles Doolittle Wolcott first encountered fossils of Pikaia in the Burgess Shale deposits of British Columbia, dating to 508 million years ago, and described them in a 1911 paper. The animal was about 16 centimeters long and ...