Parapuzosia seppenradensis, biggest known ammonite, diameter 1.80 m.

The Jurassic Period began about 201 million years ago, and the Cretaceous ended about 66 million years ago. The ammonites became extinct at the end of the Cretaceous Period, at roughly the same time as the dinosaurs disappeared. They are main index fossils, and it is often possible to link the rock layer in which they are found to specific geological time periods. About 30.000 - 40.000 species are assumed. Therefore the ammonites are very importent for geology.

Ammonites are an extinct group of marine animals belonging to the cephalopod subclass Ammonoidea. They lives from the Devonian until Late Cretaceous (417 - 65 million years ago) all over the world. Today living near relatives are coleoids, squid, octopus, and cuttlefish. Their name came from their spiral shape somewhat resemble tightly-coiled rams horns like the egyptian godhood Ammon.

The soft body of the creature occupied the largest segments of the shell at the end of the coil. The smaller earlier segments were walled off and the animal could maintain its buoyancy by filling them with gas. The shifting achieve by repulsion power.

Parapuzosia seppenradensis is the largest known species of ammonite. It lived during the Late Cretaceous period. A specimen found in Germany in 1895 measures 1.8 m (5.9 ft) in diameter, although the living chamber is incomplete. It is estimated that if complete, this specimen would have had a diameter of approximately 2.55 m (8.4 ft) or even 3.5 m (11 ft).The total live mass has been estimated at 1,455 kg (3,210 lb), of which the shell would constitute 705 kg (1,550 lb).

Many replicas of this Ammonite are standing in various museum around the world and in the town, where it was found (Seppenrade, near Münster, North Germany). The original is standing in the foyer of the "LWL-Museum für Naturkunde" in Münster (the coordinate of this cache) and it´s the logo of the museum.
Parapuzosia seppenradensis, biggest known ammonite, diameter 1.80 m. stands in the LWL-Museum of Natural History in Münster

Ammonites make excellent guide fossils for stratigraphy because:

  • they evolved rapidly so that each ammonite species has a relatively short life span
  • they are found in many types of marine sedimentary rocks
  • they are relatively common and reasonably easy to identify
  • they have a worldwide geographical distribution
  • The rapidity of ammonite evolution is the single most important reason for their superiority over other fossils for the purposes of correlation. Such correlation can be on a worldwide scale.
See also: 
Largest Spider Fossil Found in Volcanic Ash
The Largest Insect Ever Existed Was a Giant "Dragonfly"