Introduction

• Published in: Philosophical Transactions of the Royal Society of London. B, Biological Sciences
• Format: Article in Journal/Newspaper
• Language: English
• Published: The Royal Society 1985
• Subjects: North Atlantic
• Online Access: http://dx.doi.org/10.1098/rstb.1985.0067; https://royalsocietypublishing.org/doi/pdf/10.1098/rstb.1985.0067

The late Silurian-early Devonian time period, around 400 million years ago, has always attracted particular interest because of the environmental and evolutionary events that were taking place at that time. A wide ocean, called the Iapetus Ocean, which had stretched across the North Atlantic region for more than 200 million years was approaching its final closure, which resulted in the building of high mountain ranges and an extensive area of land. The borders of this new North Atlantic continent were characterized by river systems flowing from the mountain ranges into the sea. Lagoonal, brackish-water, estuarine and fluviatile conditions were widespread, and terrestial deposits also common. The semi-arid climate resulted in the oxidation of many of the deposits, giving the typical colour of the Old Red Sandstone rocks of late Silurian to Devonian age. Over the last 25 years, international debate on the positioning of the Silurian-Devonian boundary and the initiation of the I.G.C.P. project ‘ Ecostratigraphy ’ (covering Wenlock to Gedinnian strata) have intensified studies on rocks and fossils of this age. These studies have resulted in great improvements in correlation, classification and knowledge of palaeoecology, most particularly involving the invertebrate animals. In addition, because of the importance of this period in evolutionary history, a tremendous amount of detailed work has been done on the plants and the vertebrates which appear to have migrated onto the land areas around this time.