Ammonite

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

Ammonite

Scientific name

Asteroceras obtusum

Type

Molluscs > Cephalopods


Strata

Black Ven Marl Charmouth Mudstone Formation

Time period

Lower Jurassic

Age

185 million years

Where found

Charmouth

Found by

Barney Hansford

Museum

Bridport Museum

Accession number

BRPMG.1217