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The small shelly fauna is the name given to an obscure collection of small hard-shelled fossils found worldwide in beds a bit older than the earliest trilobites and archeocyathids in Nemakit-daldiyan stage (Lower Cambrian). The start of the Cambrian period had classically been set at the first appearance of small shelly fossils. Workers in a remote part of Siberia found very small hard-shelled fossils in slightly older beds in the 1980s. Similar fossils were subsequently found in corresponding beds in many other parts of the world.
The forms included diminutive specimens of known animals such as archeocyathids and brachiopods plus many small shell-like forms a millimeter or two in size. It was later recognized that the latter were fragments of body armor of a few types of animals, not complete shells of a multitude of unknown creatures. Common practice is to include the small shelly fauna in the earliest Lower Cambrian. The fauna and its relationship to more conventional later faunas is still poorly understood.
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