Devonian

The Devonian is a geologic period of the Paleozoic era around 408 million years ago also known as the Age of Fishes. The Devonian era is named after Devon, England, where rocks from this period were first studied. During the Devonian era, the planet was changing in appearance and the great supercontinent of Gondwana was heading slowly northwards away from the south pole. A second supercontinent began to form that straddled the Equator. Known as Euramerica, or Laurussia, it was created by the coming together of parts of North America, northern Europe, Russia and Greenland.

Devonian Times

The Hangenberg event sits on or just below the Devonian/Carboniferous boundary and marks the final spike in the period of extinction. The Hangenberg event was an anoxic period at the end of the Famennian epoch (late Devonian) associated with the Late Devonian extinction, marked by a black shale.

Fammenian - South American glaciation begins.

The Kellwasser event is the term given to the extinction pulse that occurs near the Frasnian/Famennian boundary. There may in fact have been two closely spaced events here.

Frasnian - Frasnian time occurred between 385.3 million and 374.5 million years ago. The stage’s name is derived from the town of Frasnes in the Ardennes region of southern Belgium. The lower boundary point of the Frasnian is defined on the basis of the first occurrence of the conodont Ancyrodella rotundiloba.

Givetian - Givetian time spans the interval between 391.8 million and 385.3 million years ago. It was named for exposures studied near Givet in the Ardennes region of northern France and is characterized by a zone (a smaller subdivision of geologic time) whose rocks include the ammonite genus Maenioceras. Widespread shrubs and trees appeared.

Eifelian - Eifelian time spans the interval between 397.5 million and 391.8 million years ago. The name of the Eifelian Stage is derived from the Eifel Hills in western Germany, near Luxembourg and Belgium.

Emsian - Emsian time spans the interval between 407 million and 397.5 million years ago. The Emsian Stage was named for exposures studied in the region of the Ems River in western Germany, where it consists of wackes (dirty sandstone) noted for their rich fossil faunas.

Pragian - Hunsruck fauna - More than 260 animal species have been described from the Hunsruck Slate. The deposits occur in a strip some 15 kilometres wide and 150 kilometres long running from northwest to southeast. In the main depositional basins of Kaub, Bundenbach and Gemünden, echinoderms are concentrated in the southwestern area around Bundenbach, with brachiopods predominating in the northeast. The presence of corals and trilobites with well-developed eyes and the rarity of plant fossils from the central basin areas suggest a shallow-water environment. Other animal fossils include sponges, corals, brachiopods, cephalopods, cnidarians, gastropods, and worm trace fossils. Trilobites and echinoderms are relatively abundant in some horizons. Crinoids and starfish are the predominant representatives of the echinoderms, although holothurians (sea cucumbers) are also represented. More than 60 species of crinoids are described from the Hunsrück Slate. Both placoderm armoured fish and agnatha jawless fish have been discovered.

and

Rhynie chert - The Rhynie chert is an Early Devonian Lagerstatte found near the village of Rhynie, Aberdeenshire, Scotland, containing exceptionally preserved plant, fungus, lichen and animal material petrified in three dimensions by covering with fast-setting volcanic minerals. The bulk of the fossil bed consists of primitive plants (which had water-conducting cells and sporangia, but no true leaves), along with arthropods, lichens, algae and fungi. The bed lies under at least 1 metre of overburden, in a single small field near the village of Rhynie, so is effectively inaccessible to collectors.

Lockhovian - The beginning of the Devonian Period which lasts until the Pragian.

More About Devonian

The Devonian is usually broken into Early, Middle, and Late subdivisions. The rocks corresponding to these epochs are referred to as belonging to the lower, middle, and upper parts of the Devonian System. As the Paleozoic era continues, we see the first appearance of land creatures, such as mites, ammonites, crabs and the first arthropods like insects and spiders also started to colonize terrestrial habitats. During the Devonian Period the first fish evolved legs and started to walk on land as tetrapods. A recently discovered fossil creature from the Devonian has been hailed as a vital link between fish and the first vertebrates to walk on land. Found in the Canadian Arctic in 2004, Tiktaalik had a crocodile-like head and strong, bony fins that scientists think it used like legs to move in shallow waters or even on land. The fish showed other characteristics of terrestrial animals, including ribs, a neck, and nostrils on its snout for breathing air.

The first seed-bearing plants spread across dry land, forming huge forests. The vegetation of the early Devonian consisted primarily of small plants, the tallest being only a metre tall. In the oceans, fish diversified into the first primitive sharks and the first lobe-finned and bony fish appeared. Early placoderms fed on mollusks and other invertebrates, but later species developed into ferocious, fish-slicing monsters measuring up to 33 feet (10 metres) long.

The first ammonite mollusks appeared, and trilobites, the mollusc-like brachiopods, as well as great coral reefs were still common. The Late Devonian extinction severely affected marine life. Towards the end of the Devonian period, amphibians began to colonize the land. The first ferns also grew and true seed plants eventually emerged. The Devonian period also saw many new groups of fish evolve.

During the Devonian, there were three major continental masses: North America and Europe sat together near the equator, much of their current land underneath seas. To the north lay a portion of modern Siberia. A composite continent of South America, Africa, Antarctica, India, and Australia dominated the southern hemisphere. The Late Devonian extinction was one of five major extinction events in the history of the Earths biota (the total collection of organisms of a geographic region or a time period). A major extinction occurred at the boundary that marks the beginning of the last phase of the Devonian period, the Famennian faunal stage, (the Frasnian-Famennian boundary), about 364 million years ago, when nearly all of the fossil agnathan fishes (jawless fishes) suddenly disappeared. A second strong pulse closed the Devonian period. Overall, 19% of all families and 50% of all genera went extinct.