The Caribbean monk seal ( *Monachus tropicalis*) went extinct in the 20th century, making it difficult to definitively assign a specific geologic time period to the species. However, we can look at its existence within the broader context of geologic time:

* Holocene Epoch: The Caribbean monk seal existed during the Holocene Epoch, which began around 11,700 years ago and continues to this day. This epoch is characterized by the current interglacial period and the rise of human civilization.

* Late Pleistocene: While the Caribbean monk seal is not typically associated with the Pleistocene epoch (which ended around 11,700 years ago), its lineage likely originated in that time period. The Pleistocene was a time of significant environmental change, including glacial cycles and the emergence of modern mammals.

Therefore, while the Caribbean monk seal existed within the Holocene Epoch and its origins trace back to the Late Pleistocene, it's important to remember that its extinction occurred within the timeframe of human history, a relatively brief period in geologic terms.