Cainozoic (from the Gr. καινός, recent, ζωή, life), also written Cenozoic (American), Kainozoisch, Cänozoisch (German), Cénozoaire (Renevier), in geology, the name given to the youngest of the three great eras of geological time, the other two being the Mesozoic and Palaeozoic eras. Some authors have employed the term "Neozoic" (Neozoisch) with the same significance, others have restricted its application to the Tertiary epoch (Néozoique, De Lapparent). The "Neogene" of Hörnes (1853) included the Miocene and Pliocene periods; Renevier subsequently modified its form to Néogénique. The remaining Tertiary periods were classed as Paléogaen by Naumaun in 1866. The word "Neocene" has been used in place of Neozoic, but its employment is open to objection.
Some confusion has been introduced by the use of the term Cainozoic to include, on the one hand, the Tertiary period alone, and on the other hand, to make it include both the Tertiary and the post-Tertiary or Quaternary epochs; and in order that it may bear a relationship to the concepts of time and faunal development similar to those indicated by the terms Mesozoic and Palaeozoic it is advisable to restrict its use to the latter alternative. Thus the Cainozoic era would embrace all the geological periods from Eocene to Recent. (See Tertiary and Pleistocene.)
(J. A. H.)