Cymbospondylus vertebrae (Ichthyosauria, Shastasauridae) from the Upper Anisian Prezzo Limestone (Middle Triassic, Southern Alps) with an overview of the chronostratigraphic distribution of the group.

Four vertebral centra from the well known fossil-bearing Prezzo Limestone (Upper Anisian, Middle Triassic) of the new locality Piazza Brembana (Bergamo) are described. The four bones were originally articulated and exposed on bed surface. Despite the incompleteness of three centra due to the erosion, the fairly good preservation allowed their study and their attribution to a shastasaurid ichthyosaur; the diapophysis reaching the cranial margin of the centrum are considered as diagnostic for the genus Cymbospondylus Leidy, 1868 (Sander 1997; Maisch & Matzke 2000). The new finding comes from an ammonoid-bearing facies, as usual for ichthyosaurs. The bio-chronostratigraphic position of Piazza Brembana bones is well constrained by ammonoids from the lowest part of the Paraceratites trinodosus Zone (Illyrian, Middle Triassic). The record of Cymbospondylus in the Southern Alps and the Germanic Basin is summarized and all the previous occurrences of the genus are bio-chronostratigraphically calibrated by using the rich ammonoid literature available. The genus spans from the Pelsonian (late Middle Anisian) to the Longobardian (Late Ladinian) and its stratigraphic distribution is strictly controlled by the development of the basins. Within the basins the distribution of the specimens seems to include relatively protected and shallow waters. Such a distribution is consistent with the mode of life of this group of ichthyosaurs, suggested by morphofunctional analysis. Cymbospondylus probably was an undulatory swimmer, better manoeuvrer but slower than their Jurassic forthcomers