What is "aalenian"

a. (context geology paleontology English) Of or pertaining to the Aalenian epoch. n. (context geology paleontology English) A subdivision of the Middle Jurassic epoch or series.

The Aalenian is a subdivision of the Middle Jurassic epoch/ series of the geologic timescale that extends from about 174.1 Ma to about 170.3 Ma (million years ago). It was preceded by the Toarcian and succeeded by the Bajocian.