Acritarchs are organic microfossils, known from approximately 1800 million years ago to the present. The classification is a catch all term used to refer to any organic microfossils that cannot be assigned to other groups. Their diversity reflects major ecological events such as the appearance of predation and the Cambrian explosion.
Acritarch from the Weng'an biota c. 570–609 mya
A microfossil is a fossil that is generally between 0.001 mm and 1 mm in size, the visual study of which requires the use of light or electron microscopy. A fossil which can be studied with the naked eye or low-powered magnification, such as a hand lens, is referred to as a macrofossil.
An enigmatic carbonaceous microfossil, Cochleatina canilovica, from the Late Ediacaran
Microfossils from a deep sea sediment core
A Late Silurian chitinozoan from the Burgsvik beds showing its flask shape
Acritarch from the Weng'an biota c. 570–609 mya