1881 E. Renevier in Proc. Geologists' Assoc. 1879–81 6 426 Cryptozoic.—Compact, Siliceous, Dolomitic, and Crystalline Limestones.

1911 Encycl. Brit. XXII. 266/2 The name pre-Cambrian is the equivalent of the ‘Algonkian’..and of the ‘Proterozoic’..; the term eozoic, archaeozoic, agnotozoic, cryptozoic, eparchaic and others have also been applied to the same period.

1930 G. H. Chadwick in Bull. Geol. Soc. Amer. 41 48 The following classificatory scheme is offered for criticism... Phanerozoic or Phanerobiotic... Cryptozoic or Cryptobiotic (Precambrian).

1958 R. C. Moore Introd. Hist. Geol. (ed. 2) iv. 59 The first major division of earth history determinable from rocks exposed at the surface is the Cryptozoic Eon.

1988 P. Cloud Oasis in Space xi. 286/2 Stromatolites have been prime targets in a successful search for new Cryptozoic biotas.

2005 Micropaleontology 51 345/1 These biotypes and their associated microbes are geologically ancient (Cryptozoic).

1922 F. W. Flattely & C. L. Walton Biol. Sea-Shore i. 7 We thus have two great sub-realms: the phanerozoic and the cryptozoic.

1949 Rep. Comm. Measurem. Geol. Time 1947–8 (National Res. Council (U.S.) Div. Geol. & Geogr.) 53 Suggests calling preCambrian the Cryptozoic, with a 3-fold division into Eo-, Meso-, and Neo-cryptozoic eons.

1968 Courier-Mail (Brisbane) 19 Nov. 26/8 The Cryptozoic (‘hidden life’) extends a further 3,000 million years—and yet its rocks show almost no traces of life!

1992 C. Emiliani Planet Earth xx. 406/1 The Cryptozoic covers the time from the formation of the solar system..to the beginning of the Cambrian.

2002 A. Sawyer in G. Westfahl et al. Worlds Enough & Time v. 56 Humanity has become too closely aware of its impending death and dissolution into the mindless mock-life among the rocks of the Cryptozoic.

1889 A. Dendy in Victorian Naturalist 5 131 To these light-abhorring animals, which live concealed under logs and stones and beneath the dead bark of trees, and venture forth from their hiding places, if at all, only at night or under exceptional circumstances, it will be convenient to give a distinct name indicative of their peculiar habitat, and..I can find no more suitable name than 'Cryptozoic', or living hidden.

1899 J. A. Thomson in H. R. Mill Internat. Geogr. i. viii. 93 There is the ‘cryptozoic’ fauna of caves and grottoes, some members of which appear to be ancient relicts.

1926 Glasgow Herald 26 June 4/2 It lives a cryptozoic life, shy and nocturnal, hiding under bark and leaves.

1953 R. F. Lawrence Biol. Cryptic Fauna of Forests ii. 32 Certain examples of cryptozoic forms may take advantage of the shelter provided by human habitations.

2003 Herpetologica 59 124/2 This agrees with diurnal, terrestrial, and cryptozoic habits recorded for T. melanocephala in the Amazon region.