Peter Van Roy, a Yale postdoctoral associate, and Derek Briggs, the Frederick William Beinecke Professor of Geology & Geophysics and director of the Yale Peabody Museum of Natural history, were among the several authors to publish on May 13 in the journal Nature their discovery of about 1,500 rare soft-bodied fossils.

Their paper, titled “Ordovician faunas of Burgess Shale type,” examines the implications of “Fezouata Biota” fossils from the early Ordovician period (approximately 490 million years ago) that they found in Morocco during a field expedition last year.

Van Roy said the study is remarkable in that it shakes up a number of long-held beliefs reinforced by a fossil record dominated by “shelly” animals. The findings, Van Roy said, are the first to demonstrate that ancient soft-bodied animals did not become extinct after the middle Cambrian period, as was previously thought, but lived much longer.

In addition, he said, the disproportionately “shelly” fossil record had, until now, led researchers to believe a widespread population decline occurred directly following the Cambrian period, after which organisms were largely replaced by Paleozoic organisms. But Van Roy and Briggs’ study shows that Cambrian organisms lived long after this supposed extinction and replacement, leading them to conclude that the turnover was much more gradual than they had originally thought, Van Roy said.