IN A WIDE ARCH

The thin shell tube of the heteromorph ammonite on the right makes an extremely fragile impression. How might this animal have lived? It is conceivable that the filigree, lightweight shell was hooked onto seagrass mats that floated on the sea surface.

Next to it is a “normal” ammonite, coiled up in a spiral, as found especially in the layers of the Jurassic period.