Gastropod evolution, phylogeny und taxonomy from upper Triassic to middle Jurassic
The time period between the Carnian (Upper Triassic) and Aalenian (Middle Jurassic) is characterized by important global and regional mass extinctions (e.g., end-Triassic and Pliensbachian/Toarcian).
Fig. 1: Eucyclus elegans (Eucyclidae) from the Liassic of Franconia (Germany, N Bavaria), c. 1 cm high (from Nützel 2008).
Similar to modern faunas, gastropods have been one of the most diverse clades during this period of time. This project is about systematics and taxonomy of several important gastropod groups: Trochidae and Eucyclidae (Trochoidea: Vetigastropoda), Cerithioidea (Caenogastropoda), Mathildoidea, and Acteonoidea (Heterobranchia). These groups are highly diverse in the sample period; their knowledge is essential for research on gastropod phylogeny. The revision of these groups facilitates the analysis of their evolutionary fate at the mentioned mass extinction events and may serve as a base for more far future analyses. The revision and documentation of the type species of genera is especially important (Museum material). In order to use the entire information content of the fossil shells, it will be tried to analyse shape, ornament, protoconch, and aperture as well as changes in time of these characters. The re-investigation of type specimens often changes the systematic placement and our understanding of of genera and families entirely. In addition, well-preserved not yet studied material is at hand and will be used for analyses.
Fig. 2: Cryptaulax armata (Cerithioidea) ) from the Liassic of Franconia (Germany, N Bavaria) (from Schulbert & Nützel 2008).
Fig. 3: Tricarilda sp. (Mathildidae) from the Liassic of Franconia (Germany, N Bavaria); a heterostrophic larval shell is typical for this group (from Schulbert & Nützel 2008).
Fig. 4: Cylindrobullina sp. (Opisthobranchia) ) from the Upper Triassic Cassian Formation (N Italy, S Dolomites); a heterostrophic larval shell is also typical for this group.
Joachim Gründel, Freie Universität Berlin