Large ornamented Ediacaran microfossils (LOEMs) are microscopic acritarchs, usually over 100 μm in diameter, which are common in sediments of the Ediacaran period, 635 to 541 million years ago. They largely disappear from the Ediacaran fossil record before 560 million years ago, 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.
Contents
Affinity
The affinity of LOEMs is a matter of current research.
Like the resting cysts of some animals, LOEMs have three layers in their cell walls. If the LOEMs do represent animal resting stages, this would be consistent with frequent periods of oceanic anoxia in the Ediacaran, which disappear in the Cambrian.
They are much larger than any known dinoflagellate, and dinoflagellate biomarkers are absent in the Ediacaran.
Green alga-related spores and cycts are generally differently or un-ornamented, and an order of magnitude smaller in diameter.
Role of spines
In the Ediacaran, predatory (cell-ingesting) organisms were just evolving. It has been suggested that the spines evolved as a defence to predation, although this argument loses weight if predation began earlier. Further, many predators are unaffected by spines, with the cyst alone providing sufficient protection from digestion.