Enigmatic Ediacara Fossils:
Ancestors or Aliens?
David J. Bottjer
THE EDIACARA FOSSILS, OF LATE PRECAMBRIAN (VENDIAN) through Cambrian age, are among the most remarkable fossil biotas known from the stratigraphic record. This stems from the fact that this biota is thought to include fossils of some of the earliest larger organisms, whose nature has been much debated: Are they ancient representatives of still extant metazoan phyla, do they represent phyla or a kingdom now extinct on Earth, or could they even be colonial procaryotes or fossil lichens? Furthermore, when compared with younger deposits, this biota is in general a taphonomic anomaly. The Ediacara fossils represent remains of completely soft-bodied organisms, and yet they are commonly preserved in coarser-grained siliciclastics deposited in relatively well oxygenated marine environments, a seemingly improbable phenomenon not known elsewhere from the marine fossil record. Because Ediacara fossil preservation is commonly associated with some sort of event bed, varying from tidal sandstones to storm beds, to turbidites and subaqueous ash falls, their taphonomic context is best thought of as obrution deposits.
Fossils we now recognize as Ediacara were discovered as early as the nineteenth century in England at the Charnwood Forest locality (Hill and Bonney 1877) and in the early twentieth century in Namibia (Gürich 1930). However, their importance was not internationally recognized until the 1940s when R. C. Sprigg, an assistant government geologist of South Australia, discovered fossils of late Precambrian softbodied organisms in the Ediacara Hills of the Flinders Range, 600 km north of Adelaide. Sprigg's (1947, 1949) discoveries led to the extensive work of Glaessner (1961, 1969, 1983, 1984; Glaessner and Wade 1966) and