Large ornamented Ediacaran microfossils are microscopic acritarchs, usually over 100 μm in diameter, which are common in sediments of the Ediacaran period, .[1] They largely disappear from the Ediacaran period fossil record before, roughly coeval with the origin of the Ediacara biota. They differ from Palaeozoic microfossils in many respects; they are larger, often have internal contents, have a differently-constructed cell wall, and differ in shape.[1]
The affinity of large ornamented Ediacaran microfossils is a matter of current research.
Like the resting cysts of some animals, these microfossils have three layers in their cell walls.[1] If large ornamented Ediacaran microfossils represent animal resting stages, this would be consistent with frequent periods of oceanic anoxia in the Ediacaran period, which disappear in the Cambrian period.[1]
They are much larger than any known dinoflagellate, and dinoflagellate biomarkers are absent in the Ediacaran period.[1]
Green alga-related spores and cysts are generally differently or un-ornamented, and an order of magnitude smaller in diameter.[1]
In the Ediacaran period, predatory (cell-ingesting) organisms were just evolving.[2] It has been suggested that the spines evolved as a defence to predation,[3] although this argument loses weight if predation began earlier.[1] Further, many predators are unaffected by spines, with the cyst alone providing sufficient protection from digestion.[1]