Dactylioceras commune, ammonite Dimetrodon land-shells

land-shells

Later discoveries found 2 more species

Ichthyostega stood alone as a transitional fossil between fish and tetrapods

ribbed shell

and Africa

Dactylioceras commune, ammonite Dimetrodon land-shellsDactylioceras was a widespread genus of ammonite from the Lower Jurassic period. They are generally small, averaging 2. 6 inches in diameter. Dactylioceras has a strong, ribbed shell. The ribs are slightly inclined forward, running over the outer edge, and either simple or forking at outer end. Though it eventually died out 180 million years ago, their style of ribbing was copied by numerous subsequent ammonite genera until the whole group became