Lower Jurassic - sun, sea and reptiles

In the area now referred to as the Swabian Alb in southern Germany, there used to be a large sea 200 million years ago − the Jurassic Sea. The whole of Europe − apart from a few islands − was flooded by this sea about 50 million years ago. It was tropically warm.

The marine deposits which evolved during this long period of time and which are the main building blocks of the Swabian Alb are subdivided into the Lower, Middle and Upper Jurassic.

As there was a lack of oxygen at the bottom of the sea of the southern German bay during the Lower Jurassic period, particularly good conditions were created for the long-term preservation of fossils. The habitat of the marine reptiles, fish, sea lilies, ammonites and belemnites which we find in the Posidonia Shale, was the open sea. At that time, the coast was located near Regensburg, that is around 200 kilometres away.

The dolphin-like ichthyosaurs are the most frequently occurring and best researched reptiles of the Jurassic. Their external form can be perfectly reconstructed due to the occacional preservation of skin and body contours all round the skeleton. Discoveries of female animals still containing embryos in their bodies show that they did not lay eggs but gave birth to babies. The largest ones could grow up to 20 m length. The marine crocodiles of the Jurassic are morphologically similar to modern river crocodiles in India. Like these, they were agile fish hunters. Fossils which are somewhat more difficult to find are those of plesiosaurs. The pterosaurs dominated the air at that time. They built their nests on the coastal cliffs like seagulls. As they were good flyers, they hunted for prey far away over the open sea. Just like bats, their bodies were covered with fur and a wing membrane stretched between their bony flight fingers. Unlike birds, they did not have feathers.

The most beautiful fossils of the Jurassic, however, are the sea lilies, Despite their appearance, they are not plants but animals related to starfish and sea urchins. They used their large coronas to filter plankton as food from the sea water. They mostly lived in large colonies together with mussels and were attached to driftwood. The largest colony worldwide at over 100 m² is displayed in the Prehistoric Museum Hauff in Holzmaden.

The most common Jurassic fossils are the belemnites, which are closely related to squids, and ammonites. For a geologist, the ammonites are the most important fossils of the Lower Jurassic period. Every layer shows its own, quite specific type of ammonite.

continue with Middle Jurassic