General
The Devonian period is known as “The Age of the Fishes” and was first used in the 1830s to describe a sequence of rocks in Devon, England.  There is a major mass extinction during the late Devonian (i.e., “Frasnian-Famennian event”) causing the tabulate-stromatoporoid reefs to disappear so completely that it took until the Triassic period to rebuild the reefs. In addition, the extinction either diminished or completely eradicated the brachiopods, trilobites, primitive fish groups, planktonic graptolites, and enigmatic tentaculites. The cause of this extinction is not clear but it has been suggested that the cause was global cooling associated with Gondwanan glaciation and/or sea-level/climatic change in conjunction with an extraterrestrial impact (e.g., comet/asteroid).
Tectonics and Paleoclimate
During the Devonian, the great super continent of Gondwanaland moves steadily north. The two continents of Laurentia and Baltica collide forming a new continent called Laurussia or Euramerica which starts to drift northward. The collision closes the Iapetus Ocean and results in the formation of several mountain ranges including the Caledonian Orogeny, Acadian/Appalachian, the Antler /Cordillerian, the Ellesmere, and the Uralian. Some of the Chinese blocks and Armorica have started to rift away from the Gondwanan margin. Siberia and the Kazakhstan terranes continued to drift northward. Both Gondwana and Euramerica are surrounded by subduction zones and are slowly traveling on a collision course. Sea levels were high worldwide and much of the land lay under underneath shallow oceans. Great shallow sandy bays, deltas, and inlets provided a prosperous home for tropical reef organisms. The rest of the planet is covered with a huge deep ocean. The Devonian was a “greenhouse age” where the climate was warm, mild, and generally dry world-wide.
Flora
 Plants transform from scattered “vegetation” clinging to water margins early in the period into the first of earth’s forests covering large areas of land. Small primitive spore-bearing vascular plants quickly evolved into great trees (e.g., Archaeopteris) stretching 30 meters or more in height. Seed-bearing plants (i.e., Gymnosperms) also appeared toward the end of the Devonian providing independence from moist habitats for reproduction thus enabling plants to expand into drier areas.
Fauna
 The warm tropical oceans of the Devonian period abound in fish, nautiloids, corals, echinoderms, trilobites, and conodonts. Sponges were represented by newly evolved siliceous forms and the association between algae, sponges, and corals that began in the Ordovician continued with flourishing reefs thriving in the warm shallow seas. During the Devonian, the hylaesponges, rugose, tabulate corals and the brachiopods reached their zenith in number and diversity.  The first ammonoids appear while the trilobites are in general decline possibly due to the increase in swimming predators such as new forms of fish and cephalopods. The Devonian saw the rapid diversification of fish especially the Placodermi, primitive sharks, Sarcopterygii (lobe-finned fish and lungfish), and Actinopterygii (conventional bony fish or ray-finned fish). Towards the end of the period the first fish-like tetrapodomorph moved ashore. Many arthropods including the first insects, eurypterids, arachnids (e.g., spiders), and primitive wingless insects invaded the land.
Meteorite Impacts on Earth
I included a list of meteorite impacts relevant to this time period as a point of  reference since many of the explanations for mass extinctions throughout Earth’s history include meteorite impact(s) as a possible cause. The meteorite impact information below was obtained from the ‘Earth Impact Database’ maintained by the Planetary and Space Science Centre, University of New Brunswick, Fredericton, New Brunswick, Canada ( www.passc.net/EarthImpactDatabase). |
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| Crater Name | Country & Continent | Diameter | Longitude | Latitude | M.Y.A. |
| Flynn Creek | United States, North America | 3.80 km (2.361 mi) | W 85° 40' | N 36° 17' | 360 |
| Piccaninny | Australia, Oceania | 7.00 km (4.350 mi) | E 128° 25' | S 17° 32' | 360 |
| Woodleigh | Australia, Oceania | 40.00 km (24.855 mi) | E 114° 39' | S 26° 3' | 364 |
| Siljan | Sweden, Europe | 52.00 km (32.311 mi) | E 14° 52' | N 61° 2' | 377 |
| Ilyinets | Ukraine, Europe | 8.50 km (5.282 mi) | E 29° 6' | N 49° 7' | 378 |
| Kaluga | Russian Federation, Asia | 15.00 km (9.321 mi) | E 36° 12' | N 54° 30' | 380 |
| Elbow | Canada, North America | 8.00 km (4.971 mi) | W 106° 43' | N 50° 59' | 395 |
| Brent | Canada, North America | 3.80 km (2.361 mi) | W 78° 29' | N 46° 5' | 396 |
| Nicholson | Canada, North America | 12.50 km (7.767 mi) | W 102° 41' | N 62° 40' | 400 |
| La Moinerie | Canada, North America | 8.00 km (4.971 mi) | W 66° 37' | N 57° 26' | 400 |
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