Parapuzosia seppenradensis is the largest known species of ammonite.Payne, J.L., A.G. Boyer, J.H. Brown, S. Finnegan, M. Kowalewski, R.A. Krause, Jr., S.K. Lyons, C.R. McClain, D.W. McShea, P.M. Novack-Gottshall, F.A. Smith, J.A. Stempien & S.C. Wang 2009. Two-phase increase in the maximum size of life over 3.5 billion years reflects biological innovation and environmental opportunity. PNAS 106(1): 24–27. It lived during the Lower Campanian Epoch of the Late Cretaceous period, in marine environments in what is now Westphalia, Germany. A specimen, found in Seppenrade near Lüdinghausen, Germany in 1895 measures in diameter, although the living chamber is incomplete.
The original fossil is shown in the foyer of the Westphalian Museum of Natural History, Münster, Germany. It was once estimated that, if complete, this specimen would have had a diameter of approximately Landois, H. 1895. Die Riesenammoniten von Seppenrade, Pachydiscus Zittel Seppenradensis H. Landois. Jahresbericht des Westfälischen Provinzial-Vereins für Wissenschaft und Kunst 23: 99–108. or even .Teichert, C. & B. Kummel 1960. Size of endoceroid cephalopods. Breviora Museum of Comparative Zoology 128: 1–7. However, a study in 2021 estimated the diameter of the largest specimens to be around . An 1898 study estimated a total live mass around , of which the shell would constitute . In contrast, a 2025 study estimated that the body weighed around based on its shell volume, which would still place it among the heaviest cephalopods.
See also
Cephalopod size
References
Kennedy, W.J. & U. Kaplan 1995. Parapuzosia (Parapuzosia) seppenradensis (Landois) und die Ammonitenfauna der Dülmener Schichten, unteres Unter-Campan, Westfalen. Geologie und Paläontologie in Westfalen 33: 1–127.