Additional images

Gender issues

The body chamber – the long last chamber in an ammonite’s shell – usually takes up the last half of the outer whorl. But in this specimen, it is considerably shorter, showing that it’s probably a mature male ammonite known as a ‘microconch’. Compare it with the large ammonite shown below it, which has a body chamber which takes up half of the outer whorl. This is thought to be a ‘macroconch’, or a mature female ammonite. In other words, the mature female ammonite was considerable larger than the male.This can be even more complicated when the mature male and female ammonites look different. In the past they have been identified as different species when they are actually the same species with a different gender.

Find out more about ammonites on the molluscs pages.

Common name


Scientific name

Asteroceras obtusum


Molluscs > Cephalopods


Black Ven Marl Charmouth Mudstone Formation

Time period

Lower Jurassic


185 million years

Where found


Found by

Barney Hansford


Bridport Museum

Accession number