Brown Jurassic (Middle Jurassic)

Although the Early Jurassic Posidonia Shale Sea lasted less than two million years, the number of its vertebrate fossils is in inverse proportion to that of the ten million year-long duration of the Middle Jurassic. Construction sites or mines in iron-rich sandstones only occasionally yield isolated reptile or fish teeth or invertebrate shells. The reason for this poor fossil record is that, in contrast to the Early Jurassic Posidonia Shale Sea, the shallow Middle Jurassic Sea was well-oxygenated and carcasses were usually broken up by scavengers and currents. However, an exception to the rule is found in the early Middle Jurassic Opalinus clay Formation. In this formation, carcasses sank deep into the seafloor, thereby avoiding disintegration. In some ammonites, such as Leioceras opalinum, the original shell is even preserved.

Ammonite: Leioceras opalinum

Ammonite: Leioceras opalinum

Nautilid: Cenoceras

Giant belemnite: Megateuthis gigantea

Starfish: Pentasteria

Bivalve: Ctenostreon proboscideum

Crustacean: Eryma mandelslohi