Arietenpflaster von Bodelshausen, (near Tübingen), detail (ruler 40 cm, 50 cm) of a 3,5 m to 2,4 m stone plate in the Paleontological Collection of the University of Tübingen. These Ammonites are an extinct group of marine invertebrate animals in the class Cephalopoda, here found in Early Jurassic ("Arietenkalk-Formation" Lias alpha3, age less than 200 million years (Ma)). The stone plate has fossils up to 70 cm. The fossile on the left is a marine mollusc of the subclass nautiloidea, of which there are still living species. The accumulation of Ammonites is a natural result of flows in a flat marine sea.