This belemnite, Belemntella mucronata, is from chalk, the very highest and youngest rocks in the Jurassic Coast World Heritage Site. This specimen is not identified to species level, but geologists can sub-divide the rocks into fine time zones defined by the presence of certain fossils because the animals evolved or changed through time. Ammonites are the best zone fossils through the Jurassic and parts of the Cretaceous periods, but at the very end of the chalk period, the presence of this belemnite is used in just the same way.
