Quaternary period

Definition

The current geological period of the Cenozoic Era, spanning approximately 2.6 million years ago to the present, encompassing the Pleistocene and Holocene epochs. In entomology and natural history, this period documents the diversification of modern insect and arachnid faunas, the extinction of Pleistocene megafauna with cascading effects on associated arthropod communities, post-glacial range shifts, and the evolution of synanthropic species alongside human expansion. The Quaternary's climatic oscillations—glacial and interglacial cycles—have left pronounced signatures in arthropod phylogeography, refugial distributions, and island biogeography patterns still visible today.

Etymology

From Latin 'quaternarius' meaning 'consisting of four,' originally the fourth division of the Tertiary; the term persisted as the period name when the Tertiary was formally subdivided.

Example

Molecular clock studies of European carabid beetles reveal Quaternary-period lineage divergences corresponding to Pleistocene glacial refugia in the Iberian, Italian, and Balkan peninsulas, with post-glacial recolonization patterns still traceable in their current distributions.

Related Terms

• Pleistocene
• Holocene
• Cenozoic
• glacial refugium
• phylogeography
• Synanthropic
• post-glacial recolonization
• Molecular clock

Usage Notes

Capitalize when referring to the formal geological period; lowercase 'quaternary' in informal contexts is discouraged in scientific writing. Distinguish from 'Quaternary' as a numerical descriptor in chemistry (four-fold substitution). The Quaternary's relatively recent definition change (formal base at 2.6 Ma, ratified 2009) means older literature may use different boundaries; check source dates when comparing studies. In arthropod research, 'Quaternary' often signals studies of extant species' recent evolutionary history rather than deep-time fossil work.