| APA | Smart Define. (2011). oligocene epoch thesaurus. Retrieved September 23, 2026, from https://smartdefine.org/oligocene_epoch/thesaurus/synonyms |
| Chicago | Smart Define. 2011. "oligocene epoch thesaurus" https://smartdefine.org/oligocene_epoch/thesaurus/synonyms (accessed September 23, 2026). |
| Harvard | Smart Define 2011, oligocene epoch thesaurus, Smart Define, viewed 23 September, 2026, <https://smartdefine.org/oligocene_epoch/thesaurus/synonyms>. |
| MLA | Smart Define. "oligocene epoch thesaurus" 26 April 2011. Web. 23 September 2026. <https://smartdefine.org/oligocene_epoch/thesaurus/synonyms> |