Biology : Semester II


IntroductionSection 1 | Section 2 | Section 3 | Section 4 | Section 5

  Section Three:

Part 1 | Part 2 | Part 3 | Part 4 | Part 5 | Part 6 | Part 7 | Part 8 | Part 9 | Part 10 | Part 11 | Part 12 | Part 13 | Part 14

Biology : The Time of Ancient Life : Part Seven

The Devonian:
Rise of the Amphibians

The Devonian period (410 to 360 million years ago) saw a continued diversification of life on the land, including the first terrestrial vertebrates, the amphibians, and the first forests of trees. In the waters fish continued their diversification with the rise of the lobe-finned and ray-finned fish. Invertebrates such as crinoids, coral, and brachiopods thrived in shallow seas during the Devonian.

Life in the Water: Invertebrates

Reconstruction of Devonian life.  Cladoselache fyleri, a 3-foot shark, was one of the top predators in the Devonian seas.

Brachiopods continued their diversification in the Devonian seas. One important group, the spiriferids, produced shells with elongated hinges, as seen in the image below. The Devonian marked the time of greatest brachiopod diversity; approximately 200 genera have been described.

Four specimens assigned to the brachiopod genus Mucrospirifer from the Middle Devonian Silica Shale of Ohio.

Rugose and tabulate coral continued to make major contributions to the formation of Devonian reefs. Crinoids and other echinoderms were prominent in many fossil assemblages.

Pachyphyllum nevadense magnum from the Martin Formation (Devonian) near Pine, Arizona.

Cephalopods also underwent an increase in forms, notably the ammonoid group known as the goniatites. These coiled, chambered nautiloids left a great many fossils, some of which are quite aesthetically appealing.

Michelanoceras, assorted ammonites from the Devonian aged Atlas Mountains Formation, Morocco. In this specimen the surrounding matrix has been cut away and the fossils cut to reveal the inner chambers.

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