[3] Sowerbyceras from the Kimmeridgian of Southern Alps (Northern Italy) show that the evolution of the Genus is strongly affected by fluctuations in sea level.

During times of high sea-level (transgressive phases = slight bottom currents) Sowerbyceras faunas decreased in numbers, and were smaller, with a lower thickness ratio Wb/D (whorl breadth/Diameter) and a more evolute conch.

A transgressive phase led to a numerically small population of Sowerbyceras that in turn resulted in low intraspecific variability and as a consequence speciation occurred.

In fact where, despite a low number of specimens, a high intraspecific variability is observed (at the top of the Beckeri-Pressulum Zone) Sowerbyceras became extinct in a short time.

This observation is extremely important and assists the understanding of the process of extinction (From: "SARTI C. - 2003, Sea-level changes in the Kimmeridgian (Late Jurassic) and their effects on the phenotype evolution and dimorphism of the ammonite genus Sowerbyceras (Phylloceratina) and other ammonoid faunas from the distal pelagic swell area of the “Trento Plateau” (Southern Alps, Northern Italy): GeoActa, Vol.2, pp.115-144") Fossils of species within this genus have been found in the Jurassic of Algeria, France, Italy, Madagascar and Spain.