In the geologic timescale, the Bajocian is an age and stage in the Middle Jurassic.
The stage was named and introduced in scientific literature by French palaeontologist Alcide d'Orbigny in 1842.
The base of the Bajocian stage is defined as the place in the stratigraphic column where fossils of the ammonite genus Hyperlioceras first appear.
A global reference profile (a GSSP) for the base is located at Murtinheira, close to Cabo Mondego in Portugal.
[5] The top of the Bajocian (the base of the Bathonian) is at the first appearance of ammonite species Parkinsonia convergens.