The Age of Fishes

370 Million Years Ago

fish_1THE SCULPTURE REPRESENTS  a placoderm fish. They had plates of bony armour on their heads and were common in the oceans of the Devonian Period, which is also known as the Age of the Fishes. The boulder is a piece of Devonian Old Red Sandstone from the Nagle Hills on the other side of the river. The sand was laid down on the land surface 370 million years ago and contains no fossils, because terrestrial plants were only beginning to evolve. While the sea was teeming with life, the land surface remained largely desert.

In the late Devonian, the first real trees did make a brief appearance, along with the first land vertebrates. It was not until the Carboniferous Period, however, that the land plants really got underway, creating vast habitats for land animals to occupy, about 315 million years ago. That will be the subject of the next station, marked by a bronze amphibian on a boulder of local limestone.

FOSSILS OF Archaeopteris sp. trees have been found in Devonian rocks at Kiltorcan in Co. Kilkenny. They were the first real trees and grew up to 30 metres tall, with fern like fronds of leaves. They grew in forests that fringed much of the world’s continents at the time.

The earliest fossils of four legged or ‘tetrapod’ animals also date from this period. In rocks on the shore of Valentia Island, Co. Kerry, the oldest tetrapod footprints in the world have been found. They are preserved in what was a muddy shoreline 385 million years ago.

The end of the Devonian is associated with one of the greatest extinction events in the history of the world. Most shallow water species of coral and fish disappeared, along with the great Archaeopteris trees. The trees may have played a part in the extinction, by introducing huge amounts of oxygen into the atmosphere, causing the melting of the polar ice caps.

At least some of the extremely rare tetrapods must have survived, as we shall see at the next station.