EduF32 Belemnite Phragmacone

3D Model

Belemnite Phragmacone (Belemnitida)

73x26x17mm

Jurassic (Oxford Clay, 166-160Ma)

Cambridgeshire, England

Belemnites are extinct marine animals, a type of mollusc related to squids, and the also extinct ammonites. They resembled squids on the outside, but had an internal skeleton called a rostrum. Inside there was a phragmacone, which like the shell of ammonites was divided into gas-filled chambers which the animal used to control whether it floats or sinks by moving water into and out of these chambers using a tube, or siphuncle. This fragile cone made of the mineral aragonite was surrounded by a thick pointy guard made of calcite for protection. Since aragonite is less stable than calcite, the guards fossilise better, with the phragmacone usually breaking or dissolving.

When found in antiquity, belemnite guards were believed to be lightning bolts thrown from the sky, as they would be washed out after a thunderstorm, or as devil’s fingers or ghostly candles, and they were also ground up as medicine.