Ediacaran Affinities: Mostly Unknown
Spriggina is an Ediacaran fossil that illustrates how difficult it has
been to classify these creatures in general.
The fossil, typically preserved in sands, on the left, has been interpreted as a segmented worm and as a frond fixed in of the substrate.
Most of the Ediacaran creatures are structurally unlike the metazoans that followed them in time. Since they were described in 1947, there has been debate about their possible relationships. Some workers have classified them as a separate kingdom; others have described the frond creatures as ancestors to sea pens, disks as primitive sea anemones, and Spriggina as an arthropod ancestor.
Illustration by Jack Unruh,
from Peter Grimes article in Discover, March, 1997.