THE GIANT PARAPUZOSIA OF NORTHEASTERN MEXICO AND THEIR RELATION TO THE WORLD’S LARGEST AMMONITE

Giant Parapuzosia fascinated the world ever since their first discovery in the Kortmann quarry near Seppenrade, Westfalen, and the publication of a giant 2.3 m in diameter in 1895 by Landois. This is still the largest ammonite known worldwide. Since then, four giant specimens are known from Europe, in addition to three undescribed specimens from England. Little is known on these specimens and the species, and giant Parapuzosia are considered to be extremely rare. Giant specimens of Parapuzosia are also known from North America and have been refered to three species, but these have never been compared to the European ones.

During cooperation activities and fieldwork in the northeastern Mexican state of Coahuila, we discovered 15 specimens of giant Parapuzosia in official and private collections and also found the locality from there these giants originate, a riverbed south of the Rio Grande near Jimenez. The section is superbly exposed, lithostratigraphically monotonous and rich in fossils. The inoceramid and ammonite record indicates that the Santonian-Campanian boundary is present. Parapuzosia is common, and we retrieved 54 individuals of varying diameters. This allows for precise biostratigraphy, for comparison with European and North American taxa, and for the study of ontogenetic stages and evolution.

Reference cited: Landois, H., 1895, Die Riesenammoniten von Seppenrade: Pachydiscus ZITTEL Seppenradensis H. LANDOIS: Jahresbericht des Westfälischen Provinzialvereins für Wissenschaft und Kunst, v. 23, p. 99-108.