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Triassic

The Triassic 250-208 million years ago

After the cataclysmic events that marked the end of the Permian Era and the extinction of 96% of all living species, you might expect the earth to be a quiet and desolate place, which it probably was for a while. But that 4% of species that survived would soon recolonise the planet and give rise to some of the most impressive creatures that ever roamed the earth – the dinosaurs.

The Triassic rocks of Shropshire illustrate that almost lifeless land quite well. Around Ruyton-XI-Towns you can see the bright red weak sandstone cut into by a thick purple pebble layer. This marks a change in the environment from dry desert to seasonal monsoon conditions.

Heavy rains falling on distant mountains left bare by the Permian desert conditions (as seen around Bridgnorth) and mass extinction would create massive rivers, ploughing a path to the lowlands of Shropshire. Along the way it would pick up mud, sand, pebbles, boulders and any trees left, fallen or standing, sweeping everything up and carrying it miles in a torrent of water and debris.

These flash floods would eventually calm down to slow, steady rivers bringing no more than sand with them from the eroded mountains. The hills to the North and East of Shrewsbury are all made from these river sandstones, Nesscliff, Grinshill and Hawkestone Park are all wonderful places to see the red and cream sandstones that are typical of Triassic Shropshire.

It took almost 10 million years for life to return in any significance. It still would not be life as we know it today, no grass or flowering plants, just mosses, ferns and conifers providing ground cover where they were able to take hold. Reptiles began to evolve into creatures that are still around today, the crocodile family. Fossil crocodiles have been found in Scotland, a world away from where they live today.

Shropshire has its own special fossils from the Triassic. A small plant-eating reptile called Rynchosaurus called Shropshire home. Its fossil remains are rather small, but it was capable of growing to the size of a small hippo. The footprints of Rynchosaurus are beautifully preserved in the working quarry at Grinshill.

Part of the reason why the climate was extreme at this time could be because during the Permian and Triassic periods all the land on the face of the earth was joined together. This created a super-continent that geologists call Pangaea, meaning 'whole earth'. Britain was right at the heart of this enormous landmass and just 25 or 30° degrees north of the equator. Massive salt lakes stretched over much of Britain and Europe as trapped sea water evaporated, leaving behind thick layers of gypsum, calcite and anhydrite, which all have important industrial uses.

By the end of the Triassic, the huge super-continent of Pangaea was starting to break up into almost recognisable landforms. This disintegration set the scene for the modern shapes of the continents that we recognise today. Meteorites again began to bombard the planet. There are several huge craters left from the impacts that have been dated to the end of the Triassic period.

As rift valleys opened and the land began to separate, shallow seas flooded the shores of the new smaller continents, giving rise to a water world and the start of an age synonymous with the dinosaurs – the Jurassic.

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