Small carbonaceous fossil

Small carbonaceous fossils (SCFs) are sub-millimetric organic remains of organisms preserved in sedimentary strata. This category of fossils has traditionally included robust or thick-walled entities such as plant spores, acritarchs and chitinozoa, but the term 'SCFs' is usually applied to more fragile remnants of animals that can only be extracted through a delicate maceration technique. SCFs are relatively widespread and abundant, and can potentially preserve both mineralized and non-mineralized parts of organisms. Since SCFs can preserve the remains of non-biomineralized organisms, they have been viewed as a relatively untapped record of animal evolution, which has the potential to circumvent some of the biases of the shelly fossil record. SCFs are typically preserved in fine-grained siliciclastic rocks, and are too small to be fruitfully examined on bedding planes. Instead, they are extracted by dissolving the rock in acid. Traditional palynological preparations involve high-energy steps such as centrifuging that destroy large and fragile fossils. In the more delicate technique pioneered by Butterfield, individual microfossils are picked from sieved acid residues by hand. The sieving stage removes crystalline residue, making it easier to extract fossils, but introduces a filter: the smallest fossils (