A new scissurelloid genus and species (Mollusca, Gastropoda) from the Late Triassic Cassian Formation

PalZ ◽  
2006 ◽  
Vol 80 (3) ◽  
pp. 277-283 ◽  
Author(s):  
Alexander Nützel ◽  
Daniel L. Geiger
Keyword(s):  
Late Triassic ◽  
Cassian Formation

scholarly journals Drivers of beta diversity in modern and ancient reef-associated soft-bottom environments

PeerJ ◽  
2020 ◽  
Vol 8 ◽  
pp. e9139
Author(s):  
Vanessa Julie Roden ◽  
Martin Zuschin ◽  
Alexander Nützel ◽  
Imelda M. Hausmann ◽  
Wolfgang Kiessling
Keyword(s):  
Water Depth ◽  
Beta Diversity ◽  
Environmental Gradients ◽  
Priority Effects ◽  
Spatial Distance ◽  
Late Triassic ◽  
Minor Role ◽  
Compositional Variation ◽  
Soft Bottom ◽  
Cassian Formation

Beta diversity, the compositional variation among communities, is often associated with environmental gradients. Other drivers of beta diversity include stochastic processes, priority effects, predation, or competitive exclusion. Temporal turnover may also explain differences in faunal composition between fossil assemblages. To assess the drivers of beta diversity in reef-associated soft-bottom environments, we investigate community patterns in a Middle to Late Triassic reef basin assemblage from the Cassian Formation in the Dolomites, Northern Italy, and compare results with a Recent reef basin assemblage from the Northern Bay of Safaga, Red Sea, Egypt. We evaluate beta diversity with regard to age, water depth, and spatial distance, and compare the results with a null model to evaluate the stochasticity of these differences. Using pairwise proportional dissimilarity, we find very high beta diversity for the Cassian Formation (0.91 ± 0.02) and slightly lower beta diversity for the Bay of Safaga (0.89 ± 0.04). Null models show that stochasticity only plays a minor role in determining faunal differences. Spatial distance is also irrelevant. Contrary to expectations, there is no tendency of beta diversity to decrease with water depth. Although water depth has frequently been found to be a key factor in determining beta diversity, we find that it is not the major driver in these reef-associated soft-bottom environments. We postulate that priority effects and the biotic structuring of the sediment may be key determinants of beta diversity.

The effect of preservation on diversity in a Triassic reef basin assemblage

2021 ◽  
Author(s):  
Vanessa Julie Roden ◽  
Alexander Nützel ◽  
Wolfgang Kiessling
Keyword(s):  
Biotic Interactions ◽  
Priority Effects ◽  
Late Triassic ◽  
Strong Increase ◽  
Predator Prey ◽  
Cassian Formation ◽  
Tropical Reef ◽  
Fossil Assemblages ◽  
Benthic Ecosystems ◽  
High Beta

<p>Taphonomic effects complicate the assessment of variations in biodiversity over time. Most pre-Cenozoic fossil assemblages have been altered through taphonomic effects, such as lithification and aragonite dissolution. Several studies have found alpha (local) and gamma (global) diversity in marine ecosystems to be low in the early Mesozoic and then increase throughout the Mesozoic, reaching a maximum in the Cenozoic.</p><p>The Middle to Late Triassic Cassian Formation, exposed in the Dolomites, Southern Alps, northern Italy, comprises tropical reef basin and transported platform assemblages characterized by high diversity and commonly excellent preservation of fossils. The Cassian Formation yields high alpha (mean species richness per locality: 96), beta (mean Jaccard dissimilarity: 0.95), and gamma (1421 invertebrate species) diversity. The high primary diversity is probably due to the tropical reef-associated setting, and its reduced taphonomic alteration caused 4.5 times higher biodiversity to be preserved than in comparable pre-Cenozoic settings. High beta diversity can be explained by the presence of various habitat types and may also have been driven by priority effects. The Cassian fauna, like most comparable modern ecosystems, features a large number of gastropods (39% of all invertebrates, 58% of mollusks are gastropods). Especially small species in the millimeter size range contribute to the large number of gastropod species in the Cassian Formation. Our results support the assumption that the Modern Evolutionary Fauna was already established early in the Mesozoic and that the scarcity of small gastropods in many fossil assemblages is a taphonomic phenomenon. This contradicts the view that the major radiation of gastropods and the generally very strong increase in biodiversity largely took place in the Cenozoic. We suggest that highly complex, gastropod-dominant marine benthic ecosystems are as old as Middle/Late Triassic, pointing to an earlier establishment of the Modern Evolutionary Fauna than previously assumed. An improved eco-space utilization by infaunalization and increased biotic interactions such as a predator/prey escalation may have contributed to the high biodiversity and may reflect early aspects of the Marine Mesozoic Revolution.</p>

scholarly journals Diversity patterns of Middle Permian gastropod assemblages from the Tak Fa Formation, Central Thailand

2021 ◽  
Author(s):  
Chatchalerm Ketwetsuriya ◽  
Imelda M. Hausmann ◽  
Alexander Nützel
Keyword(s):  
Marine Invertebrate ◽  
Diversity Indices ◽  
Taxonomic Composition ◽  
Depositional Environments ◽  
Middle Permian ◽  
Late Triassic ◽  
Diversity Gradient ◽  
Cassian Formation ◽  
Central Thailand ◽  
Rank Abundance

AbstractMiddle Permian marine invertebrate assemblages from Central Thailand are strongly dominated by gastropods. Two gastropod assemblages from the Tak Fa Limestone at Khao Noi and Khao Chao Thong of the Nakhon Sawan area are the first Permian ones from Thailand that are analysed regarding diversity and composition based on quantitative data. Both gastropod assemblages, comprising 40 species in total, are dominated by the gastropods Anomphalus sp., Warthia cf. brevisinuata and Glabrocingulum magnum; the genus Anomphalus is especially abundant which is unusual for Permian assemblages. Both studied gastropod assemblages have a similar taxonomic composition and diversity including the same values of diversity indices that indicate a moderate diversity. In addition, rarefaction analyses and rank-abundance distributions also suggest that diversity and structure of both assemblages are the same. The studied assemblage is compared with other Permian gastropod assemblages from Asia (Malaysia, East Timor and Japan). Rarefaction, diversity indices and rank-abundance distributions suggest that the diversity of the studied fauna is distinctly lower than that of the others despite coming from similar depositional environments. This is surprising because the Tak Fa gastropods lived at lower latitudes than the others. This could suggest an inverse diversity gradient in the Palaeo-Tethys, but more evidence is needed to substantiate this assumption. Several Late Palaeozoic and Early Mesozoic fossil assemblages are dominated by gastropods, e.g. those from the Pennsylvanian Buckhorn Asphalt deposit, the Permian from Japan and Malaysia, as well as the Late Triassic Cassian Formation. This shows that at least locally, gastropod dominance is not restricted to modern faunas.

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