Paleogene

This term is a specialized geological designation used primarily in academic, scientific, and paleontological contexts. It carries a neutral, descriptive tone and is almost always capitalized when referring to the specific geological period, though it may appear in lowercase when used as a general adjective describing the era's characteristics.

As a proper noun referring to a specific span of geologic time, it is treated as an uncountable entity. It does not have a plural form because it describes a unique, singular interval in Earth's history.