Most types of ciliates have no hard parts, and their fossils are extremely rare; a very few have been found preserved in amber (fossiized tree resin) or by extremely fast phosphatization under unusual conditions in marine environments.
One group of cilliates, however, has a fairly extensive fossil record; this is the marine taxon Tintinnida. Tintinnid ciliates form stiff, vase-shaped or barrel-shaped coverings, called loricae, around themselves. These loricae may be mineralized or may incorporate tiny pieces of rock, and can be found as identifiable microfossils. Tintinnids first became common in the Jurassic, but their fossil history goes back at least to the Ordovician.
A second group of vase-shaped microfossils, the chitinozoans, resemble tintinnids and might represent fossil ciliates; chitinozoans go back into the late Precambrian.