Ammonites are an ancient group of cephalopod molluscs that appeared in the Early Devonian period (about 415 million years ago) and became extinct at the end of the Cretaceous period (about 66 million years ago). They are among the most common fossils of sedimentary rocks and were so abundant in the Jurassic period that they gave their name to a rock unit, the Rosso Ammonitico Veronese. The museum exhibits several ammonites from both Italian and foreign sites, many of them large, with a diameter of over 30 cm. These molluscs, apparently similar to the extant Nautilus, often had a planispirally coiled shell whose diameter ranged from a few centimetres to over a metre. The shell was subdivided internally into chambers, and the last one – the largest – was occupied by the animal. Ammonites are considered excellent “index fossils” and are used for relative dating and correlation of the rocks that contain them. This is because they experienced a rapid evolution, with several variations – some particularly unusual – in the morphology of the shell. They were also widespread and abundant in the seas all over the world.
