What are Acritarchs? Acritarchs are spherical microfossils that look very much like the resting stage cysts of dinoflagellates and other algae. Some have spines; some are completely bare; but all lack some of the characteristic features of dinoflagellate cysts. These enigmatic fossils may belong to many different groups. Acritarchs first appeared in the fossil record in the Precambrian about 1.8 billion years ago, and they are still around today.
First known fossil occurrence: Precambrian.
Last known fossil occurrence: Quaternary. This group has living relatives.