Two for the price of one!
This ammonite, called Kerberites, is an important ammonite in the Portland Limestone because it enables the rocks to be dated relative to places as far away as Greenland and Russia. That is because similar ammonites are found at those places and as ammonites evolved quickly through time, they must have lived in the same period.
Under the ammonite, you’ll also see a gastropod with a spiral shell called a Portland Screw. This tells us that the rock is Portland Roach as this is the only rock with this kind of gastropods in it.
Find out more about ammonites on the molluscs pages.