High diversity in the Triassic Cassian Formation

Roden V, Hausmann IM, Seuß B, Nützel A, Kießling W (2018)

Publication Language: English

Publication Type: Conference contribution, Abstract of lecture

Publication year: 2018

Event location: Bonn


The Middle to Upper Triassic Cassian Formation (Dolomites, Northern Italy) is the most diverse early Mesozoic ecosystem worldwide. A compilation of taxa described from the Cassian Formation contains 1336 species after revision. The species richness is very high compared with other fossil lagerstätten known for their diversity. For example, 228 species are reported in the Early Cambrian Chengjiang biota, 280 from the Upper Carboniferous Mazon Creek fauna, 491 from the Eocene London Clay, 147 from the Lower Devonian Hunsrück Slate, a literature compilation of the Upper Carboniferous Finis Shale of Texas yields 332 species, and a total of 861 animal species is reported from the Upper Jurassic Solnhofen Formation. Although the Cassian Formation stands out in the fossil context, a much higher species richness is recorded in Recent tropical ecosystems. For example, a comprehensive survey in New Caledonia, south-west Pacific, yielded 2738 species of molluscs alone (P. Bouchet et al., 2002). With gastropods comprising 70 % of mollusc species (53 % of all species), it is clear that aragonite preservation has a large impact on the diversity of the Cassian fauna. In general, fossil lagerstätten can yield highly diverse communities due to preservational effects. To assess the degree to which the Cassian diversity is driven by a lagerstätten effect, we compare the proportion of stratigraphic singletons among well-known lagerstätten (Chengjiang biota, Hunsrück Slate, Mazon Creek fauna, Solnhofen, London Clay). Among those, the Cassian Formation yields the lowest proportion of singleton genera (17%), and next to lowest proportion of singleton species (68%). The lagerstätten effect is therefore lower than in most other datasets. We consequently conclude that intensive taxonomic work and preservational bias are not the only factors contributing to the high diversity. Beyond the large area (at least 500 km2) and variety of environments covered by the Cassian Formation, yielding a very high beta diversity (mean proportional dissimilarity of 0.94), as well as aragonite preservation, the favorable living conditions in this tropical reef-basin allowed a high dlyiverse fauna to flourish.

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Roden, V., Hausmann, I.M., Seuß, B., Nützel, A., & Kießling, W. (2018). High diversity in the Triassic Cassian Formation. Paper presentation at GeoBonn2018, Living Earth, Bonn.


Roden, Vanessa, et al. "High diversity in the Triassic Cassian Formation." Presented at GeoBonn2018, Living Earth, Bonn 2018.

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