What is the name of the largest fossilized ammonite ever found?

The largest fossilized ammonite ever found is Parapuzosia seppenradensis. This enormous Late Cretaceous cephalopod is known from a famous specimen discovered near Seppenrade, Germany, in 1895.

The preserved shell measures roughly 1.7 to 1.8 meters across, although its living chamber—the section occupied by the animal—was incomplete. Estimates for the complete shell have varied widely, from about 2 meters in modern reassessments to older estimates of 2.55 or even 3.5 meters. That uncertainty explains why museum labels and reference works may quote different measurements.

Parapuzosia lived during the Lower Campanian, roughly 80 million years ago, in a marine environment covering what is now Westphalia. The original specimen is displayed at the Westphalian Museum of Natural History in Münster.

A frequent trap is Pachydiscus seppenradensis, which appears in older literature as a synonym or former classification rather than the preferred current name. The other options are ammonite genera or species, but none is the standard answer to the superlative “largest ammonite.”