Amgueddfa Cymru holds fine specimens of prehistoric marine animals, related to the dinosaurs, that swam off the coast of south Wales. Specimens from Dorset illustrate how, once, an ancient sea linked the two areas.
About 210 million years ago the small part of the Earth's crust that is now Wales lay well to the south of its present latitude, probably close to the northern tropics, where the land formed part of a huge supercontinent called Pangaea. Our climate was hot and humid, with much of Wales comprising barren uplands surrounded by desert-like mudflats. To the south, and spreading far across into Europe, was a series of large lakes.
As the continents drifted northwards the crust broke up and at various times the seas rose and spread across the land. With these spreading seas came new marine animals that we now see fossilised in the rock record. Some of the most beautiful and spectacular are the marine reptiles known as ichthyosaurs (literally, 'fish lizards'), which were distant cousins of the land-living dinosaurs.
By 200 million years ago, early in the Jurassic Period of geological time, the sea covered southernmost Wales. On the sea-floor, a blanket of fine lime sands and muds was deposited, which have since been compacted into the horizontally bedded mudstones and limestones forming the familiar cliffs in the Lavernock area and extending westwards from Barry to Southerndown.
Ichthyosaur remains are not uncommon in these rocks, although they are mostly found as isolated teeth and bones. The fragmentation took place following the death of the animals, when the skeletons were broken up by currents and wave action. Only rarely have more complete specimens been found in south Wales. In contrast, rocks of the same age in Somerset and Dorset have long been known as a rich source of complete or almost complete ichthyosaur skeletons.
The early Jurassic sea extended from the shoreline area of southern Wales across south-west England and beyond to central Europe. In the progressively offshore, deeper-water areas to the south, wave action and coastal currents were weaker, so skeletons were more likely to sink to the sea floor and remain more or less intact. Even so, such skeletons are still found only comparatively rarely today, so we are very lucky to have several almost complete ichthyosaurs in our collections from Lyme Regis in Dorset. Some of the most impressive are on display in the exhibition Evolution of Wales at National Museum Cardiff.
The fact that 200 million years ago the sea was continuous from south Wales across to Dorset means that we can use these beautiful fossils to illustrate part of the history of our area. The Dorset fossils are the same species as those found in the Glamorgan cliffs, and the animals would have been swimming freely between the two regions.
The specimens on display show beautifully the streamlined, dolphin-like shape of the ichthyosaurs. They were adapted superbly for rapid swimming, with propulsion by a large, vertical tail and steering with four flipper-like paddles. Their diet probably consisted mostly of fish and squid.