Ocean dwellers of Avalon

Natural History, July-August, 2003 by Stephan Reebs

Paleontologists once thought the shells and bones left by the organisms that emerged from the Cambrian explosion, some 545 million years ago, were remnants of Earth's earliest complex life-forms. But then fossils of earlier, soft-bodied creatures, now called Ediacarans, began to come to light. Recently the oldest such fossils in the world were discovered, on the Avalon peninsula at the southeastern tip of Newfoundland. Among them was a new species, Charnia wardi.

C. wardi grew to as much as six feet long but less than three inches wide, with slender, plantlike fronds branching off a midline. The organism was discovered, along with a less slender, equally ancient, and better-known cousin, C. masoni, in a rock formation 575 million years old. Guy M. Narbonne and James G. Gehling, both geologists at Queen's University in Kingston, Ontario, note that the creatures' fossil fronds lie parallel to one another, suggesting the Charnia were attached to the seafloor, and were reclining in a strong current before being covered by volcanic ash.

The fossils' age places them right on the heels--geologically speaking--of the last planetwide glaciation, 580 or so million years ago. Perhaps the aftermath of the freeze created the conditions for the rapid evolution of multicellular life [see "The Longest Winter," by Gabrielle Walker, April 2003]. Another possibility is that the Ediacarans evolved just before the glaciation and managed to live through it. ("Life after snowball: The oldest complex Ediacaran fossils," Geology 31:27-30, January 2003)

Stephan Reebs is a professor of biology at the University of Moncton in New Brunswick, Canada, and the author of Fish Behavior in the Aquarium and in the Wild (Cornell University Press).