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The exceptional character of the Osteno fossil site is tied to the presence of a very well-diversified and heterogeneous fauna with polychaetes, nematods, enteropneustes, decapod crustaceans, cephalopod mollusks, teleost fishes and chondrichthyes which have been exceptionally well-preserved within a calcareous rock. The fine micritic sediment has allowed for the fine preservation of soft tissues down to the cellular structure. Notwithstanding the high quality of the preservation of the Osteno fauna, oddly only a few of the fossils have been studied with some detail.

Osteno is situated in the Como Province, in Lombardy, above the Eastern shore of the Lugano lake, close to the Swiss border. The fossil site was discovered by pure chance when, in 1964, a local fossil amateur found the remains of fossil crustaceans on two slabs on the lateral columns of a gate of a private property. The latter belonged to the owner of a local quarry who gave several further specimens to the fortunate collector. In his turn, he informed the personnel of the Natural History Museum in Milan, which undertook a long series of excavations, recovering a high number of fossils, comprising about 30 specimens of crustaceans, 22 fishes, 2 plants and 11 specimens of uncertain affinity. The latter, at first thought to be cirripeds, were later found to belong to a new class of arthropods, the Thylacocephala, with the new species Ostenocaris cypriformis. These specimens held remains of the original muscles, stomach with food residues, gills, nervous system and a large cephalic sac of unknown significance.

Further reading

Arduini P., Pinna G. & Teruzzi G. (1981). A new unusual lower Jurassic cirriped from Osteno in Lombardy: Ostenia cypriformis (preliminary note). Atti della Società Italiana di Scienze naturali e del Museo civico di Storia naturale in Milano 122: 462-468.

Arduini P., Pinna G. & Teruzzi G. (1982). Melanoraphia maculata n.g. n.sp., a new fossil polychaete of the Sinemurian of Osteno in Lombardy. Atti della Societa Italiana di Scienze naturali e del Museo civico di Storia Naturale in Milano 123: 462-468.

Arduini P,. (1988) – Microcaris and Atropicaris, two genera of the class Thylacocephala. Atti della Societa Italiana di Scienze naturali e del Museo civico di Storia Naturale in Milano 129: 159-163.

Bonci M.C. & Vannucci G. (1986). I vegetali sinemuriani di Osteno (Lombardia). Atti della Società italiana di Scienze naturali e del Museo civico di Storia naturale in Milano 127: 107-127.

Bottjer D. J., Etter W., Hagadorn J. W. & Tang C.M. (2002). Exceptional Fossil Preservation. Columbia University Press: 251-264.

Garassino A. (1996). The family Erymidae Van Straelen, 1924 and the superfamily Glypheoidea Zittel, 1885 in the Sinemurian of Osteno in Lombardy (Crustacea, Decapoda). Atti della Societa Italiana di Scienze naturali e del Museo civico di Storia Naturale in Milano 135: 333-373.

Pinna G. (1967). Decouverte d’une nouvelle faune à crustacés du Sinémurien inférieur dans la région du lac Ceresio (Lombardie, Italie). Atti della Società di Scienze Naturali e del Museo Civico di Storia Naturale di Milano 106: 183-185.

Selva A. (2009). Alla ricerca dei fossili nei monti e nelle cave del Lario e del Ceresio. Maggioli Editore.

Text by Luca Jaselli

Pictures courtesy of Museo di Storia Naturale di Milano

Thanks to Alessandro Garassino for helping with information and recovery of the photographs

(partially in English)