These large gastropods were ornamented with spines or tubercles, partly to reinforce their shells and partly to be able to hide in amongst the gravel right at the contact with the rough waters, where this association used to live. The organisms were then transported into deeper waters forming the deposits we now call 'Pachycardia Tuff'.

These spherical snails could grow to a considerable size and were able to remain stable on powerful waves thanks to their smooth surface. We can imagine these molluscs were brightly coloured, as a few specimens reveal traces of colour, even if we do not know yet which colour they were.

This bivalve mollusc makes up 90 percent of the fossils in the Pachycardia Tuff layers, which explains where they got their name from! These layers of coarse sediments (sandstone and conglomerates with rounded gravel of volcanic origin) are only found on Alpe di Siusi and represent deposits containing organisms that lived on the beaches of the volcanic islands, where the waves were very strong. Pachycardia has a very thick shell that made it resistant to the force of water.