noun
Oligocene epoch
Geological epoch from about 33.9 to 23 million years ago, between the Eocene and Miocene.
漸新世は哺乳類の多様化が進んだ時代である。
The Oligocene was a period when mammalian diversification advanced.
From 漸 (ぜん, 'gradually') + 新 (しん, 'new') + 世 (せい, 'epoch'), a calque of the English 'Oligocene' (from Greek oligos 'few' + kainos 'new').