Dactylioceras

Dactylioceras was a widespread genus of ammonites from the Lower Jurassic period,[1] approximately 180 million years ago (mya).

Etymology
The name Dactylioceras comes from the Greek dactyl, meaning “finger”, and refers to the shell’s branching ribs.

Description
Dactylioceras are generally small, averaging 65 millimetres (2.6 in) in diameter. They have a strong, ribbed shell. The ribs are slightly inclined forward, running over the outer edge, and either simple or forking at outer end. Though they eventually died out 180 mya, their style of ribbing was copied by numerous subsequent ammonite genera until the whole group became extinct 66 million years ago with the dinosaurs.