Interpreting ammonite fossils

Neale Monks (UK) Ammonites are such popular and well-known fossils that suggesting they need interpreting may seem ridiculous. But for all their familiarity, there is still a good deal of debate over how they lived and what they did. If nothing else, ammonite experts all agree that they were ecologically diverse, with different species doing different things, and broadly speaking, they can be divided into ammonites that moved about close to the bottom, ammonites that actively swam about in mid-water and ammonites that drifted about on currents, rather like modern jellyfish. The aim of this article is to help you extract the maximum amount of information from the ammonite fossils in front of you. The way an ammonite shell coils is important, but so too are things like the shape of the suture line and the ornamentation visible on the surface of the fossil, which means that even fragmentary specimens can be quite informative. But first, you need to find your fossils … Where to collect ammonites Fig. 1. Folkestone, Kent. Ammonites only lived in marine environments, most often in moderately deep seas where water chemistry and salinity were more or less constant. So, the classic places to find ammonites are marine limestones (including chalks and oolites), marls, clays and shales. While ammonites seem to have inhabited a range of environments including reefs, their fossils are only occasionally common in places where coral reefs or crinoids dominate. On the other hand, sediments that contain lots of oysters, bivalves, belemnites and … Read More