Crinoid sea lily
Unlike other crinoids, Marsupites did not attach itself to hard rocks with roots but probably lived partially buried in the soft sea bed. It is an unusual and distinctive fossil that only lived for a short period of geological time – as a result it can be used to date the relative age of the chalk in which it is found. In the same way, the rapidly-evolving ammonites are used to date the older Cretaceous and Jurassic rocks.
Find out more on the echinoderms page.