Turbidites of ash roiling downslope into deep water killed and preserved a suite of Ediacaran organisms as surely as air-borne ash killed and preserved unfortunate humans at Pompeii

Field photograph of spindle-shaped fossils from Mistaken Point (David Rudkin, Royal Ontario Museum)

Of all the places to collect fossils in Canada, the rain-slicked cliffs above the Atlantic Ocean at Cape Race in Newfoundland certainly ranks among the most challenging. Mistaken Point forms a small headland on the Avalon Peninsula, just southwest of Cape Race. Here, the steeply dipping sandstone and shale beds are perennially wet and the cliffs are often shrouded in cold fog rolling in from the sea ice off-shore. But if you are lucky to be there on a rare sunny day in summer, you might see hundreds of peculiar spindle-shaped and feather-like impressions on the upper surfaces of many of the shale beds highlighted by the late afternoon rays. These imprints are the oldest Ediacaran fossils known in the world and the only ones that lived in deep water.

Ediacaran fossils were first discovered in the Flinders Range, South Australia in coarse sandstones lying beneath rocks with the first shelly fossils of Early Cambrian age. These are large, flat and carpet-like fossils. The initial work indicated that they were metazoans; that is, true animals -- medusoids, sea pens and annelid worms, possibly even arthropods and echinoderms -- and that they were soft-bodied precursors to animal groups found in Cambrian rocks. This traditional view was challenged by Dolf Seilacher, an iconoclastic German academic paleontologist, who declared that the Ediacaran fossils were not animals because none shows any evidence of having organs, muscles, mouth, anus, gut or legs. Instead he interpreted the Ediacarans as unique quilted and immobile organisms constructed as a series of fluid- or jelly-filled cells -- like air-mattresses -- that must have absorbed sunlight and nutrients directly from seawater through their skin. Seilacher suggested that these fossils represent a new kingdom of organisms called Vendobionta that became extinct before the beginning of the Cambrian.

The emblematic Mistaken Point fossil is a unique and still unnamed spindle-shaped form consisting of leaf-like compartments growing out off-set from a conspicuous mid-line. As this organism grew, the number of compartments remained constant, but each expanded and folded in a fractal pattern according to the terminology of the mathematician Benoit Mandelbrot. In this way these organisms were able to grow from a length of 5 cm to 30 cm and as wide as 9 cm. These fossils are occasionally found broadly flexed, but because they are never creased or kinked, the living organism must have been rather tough and stiff.

Dolf Seilacher called up rather compelling Biblical imagery when he referred to a peaceful Garden of Ediacara where organisms lived side by side without conflict and without predators. The life in this Garden was annihilated by the emergence of mobile animals with shells, exoskeletons and eventually claws and teeth. The naked immobile Ediacarans were defenceless and they perished worldwide.

Further reading: