Ever since their discovery in 1909, the spectacular Burgess Shale outcrops in the Canadian Rockies have presented scientists with a cornucopia of evidence for the “explosion” of complex, multicellular life beginning some 550 million years ago.
But the fossil record then goes dark: the Cambrian-period innovations in life appeared to have few clear descendants. Many scientists thought that the likely explanation for this mysterious disappearance was that a major extinction had wiped out much of the distinctive Cambrian life. It seemed that the complex organisms emerging in the Cambrian had come to an abrupt demise, disappearing with few traces in the later fossil record.
Not everyone was convinced, however, and now a trove of 480-million-year-old fossils in Morocco appears to strike a blow to the idea of a major extinction. The international team of scientists who discovered the 1,500 fossils said their find shows that the dark stretch in the fossil record more probably reflects an absence of preservation of fossils over the previous 25 million years.