Why is the Silurian called the Silurian?
Recently we took a small party to some locations we know in the county of Shropshire where you can find fossils of brachipods, bivalves, coral and such like. Shropshire’s geology is strongly associated with the Silurian period (it lasted from approximately 435mya to 410 mya), indeed two of the epochs within the Silurian are named from places in the county – the Ludlow and Wenlockian epochs. However, geologists in North America have different terms for rocks of this age from the Silurian (the Lockportian and the Tonawandan).
The Silurian marks a period of sea level rises (called marine transgressions), much of the county was covered in warm, shallow seas, during this time and marine life flourished. The beginning of the Silurian (Silurian/Ordovician boundary) is marked by a major extinction event but by the time the rocks that form Wenlock Edge were laid down life was once again flourishing with jawed fish such as the placoderms and acanthodians beginning to diversify. The arthropods continued to dominate and were the top predators during this period. The first corals were forming in these shallow seas, made by the now extinct rugose and tabulate corals.
Whilst on our fossil hunting trip we were asked how the Silurian got its name. The Silurian was named by Sir Roderick Murchison, the wealthy Scottish aristocrat. Sir Roderick had thought in the wars against Napoleon but when these ended he turned his attention to the embryonic science of geology. Encouraged by friends such as the Reverend William Buckland (the very same William Buckland who named and described the very first dinosaur – Megalosaurus); he explored the fossil-bearing strata of south Wales and Shropshire. Being independently wealthy Sir Roderick was able to mount expeditions to explore the geology of Europe and his connections soon saw him elected to the London Geological Society.
Sir Roderick named the rock strata that made up the chronological succession of fossils the Silurian after an ancient Welsh Celtic tribe called the Silures. At the time, his friend and colleague Adam Sedgwick (Professor of Geology at Cambridge University) had just named the much earlier rock strata where the first great abundance of fossils had been found – the Cambrian, after another ancient Welsh tribe.
Silurian strata shows the first signs of the colonisation of the land with the establishment of primitive vascular plants such as Cooksonia. During this time the first arthropods ventured onto land.