Microderoceras birchi is named after Colonel Thomas Birch, a contemporary and friend of Mary Anning. Microderoceras is reasonably easy to identify, having two short, blunt spines on each rib. The really unusual feature of this ammonite is the length of the body chamber – the final long chamber in which the soft parts were housed. In most ammonites, the body chamber takes up the last half of the outer whorl. But in Microderoceras, the body chamber is more than the whole outer whorl, marked in this specimen by the dark colour, which has been filled with mud. The chambered shell is preserved in yellow calcite and is therefore quite different.
Find out more about ammonites on the molluscs pages.