This type of ammonite is not streamlined in shape and was probably a poor swimmer. Ammonites from the Lower Chalk did all sorts of strange things. Some became knobbly, like this one, but others started to uncoil, or coil like a snail. It is thought that climate change stressed the ammonites and they started to experiment with shape and form as a result.
Find out more about ammonites on the molluscs pages.