11. The second came 360 million or so years ago during the Devonian Period . 12. During the Devonian period the local seas deepened and their oxygen levels dropped. 13. The fault is most likely younger than the Jacobsville Formation and the Devonian Period . 14. Paleogeographic reconstruction showing the Michigan Basin area during the Middle Devonian period . ]] 15. The oldest types of tetrapod tail-and-foot prints date back to the latter Devonian period . 16. During the Devonian period , vascular plants diversified and spread to many different land environments. 17. The formation of the Ausable Arkona has exposed fossils from the Middle Devonian period . 18. Paleogeographic reconstruction showing the Appalachian Basin area during the Middle Devonian period . ]] 19. Up to long, these eurypterids are found from the Ordovician to the Devonian periods . 20. This occurred around 370 million years ago ( in the Late Devonian period ).
