Berriasella

Berriasella is a discoidal evolute perisphinctacean ammonite, and type genus for the neocomitid subfamily Berriasellinae. Its ribbing is distinct, consisting of both simple and bifurcated ribs that extend from the umbilical seam across the venter; its whorl section generally compressed, the venter more or less narrowly rounded. The species "Berriasella jacobi" traditionally has been regarded an index fossil defining the base of the Cretaceous, however since 2016 this had been replaced by the first occurrence of "Calpionella alpina".
"Berriasella", named by Uhlig, 1905, is known from the late Upper Jurassic, Tithonian, to the early Lower Cretaceous, Berriasian and has a fairly worldwide distribution.
Distribution.
Fossils of "Berriasella" have been found in: