| 1. |
- Brosse, Morgane, et al.
(författare)
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Conodonts from the Early Triassic Microbialite of Guangxi (South China) : Implications for the Definition of the Base of the Triassic System
- 2015
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Ingår i: Palaeontology. - : Wiley. - 0031-0239 .- 1475-4983. ; 58:3, s. 563-584
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Tidskriftsartikel (refereegranskat)abstract
- We describe a new Early Triassic (Griesbachian) succession of conodont faunas from a high-resolution sampling of the basal Early Triassic microbial limestone and the base of the overlying unit at the Wuzhuan section (Nanpanjiang Basin, Guangxi, South China). The microbial limestone records the earliest phase of the Early Triassic biotic recovery after the end-Permian mass extinction. For the first time, rich conodont faunas are reported from within the microbialite. The faunas from Wuzhuan are largely dominated by anchignathodontids, including several Isarcicella species, which were previously documented only from strata above the microbialite. A total of 14 conodont species assigned to three genera is recorded from the Wuzhuan section. Starting from the base of the microbialite upwards, several species are sequentially added to the conodont assemblage. The alpha diversity peaks at the top of the microbialite. The conodont record in the considered microbialite interval at Wuzhuan is presumably unaffected by local ecological changes. It therefore more likely represents an evolutionary rather than an ecological pattern. We compare the Wuzhuan's conodont record with a well-supported phylogenetic model and suggest that the sequence of first occurrences at Wuzhuan is the closest to the true' sequence of evolutionary events that took place during this Griesbachian radiation of anchignathodontids. Based on comparisons with the GSSP section at Meishan, we suggest further that the first occurrence of Hindeodus parvus in Meishan does not correspond to its first appearance datum.
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| 2. |
- Hautmann, Michael, et al.
(författare)
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Competition in slow motion : the unusual case of benthic marine communities in the wake of the end-Permian mass extinction
- 2015
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Ingår i: Palaeontology. - : Wiley. - 0031-0239 .- 1475-4983. ; 58:5, s. 871-901
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Tidskriftsartikel (refereegranskat)abstract
- Changes of community structure in response to competition usually take place on timescales that are much too short to be visible in the geological record. Here we report the notable exception of a benthic marine community in the wake of the end-Permian mass extinction, which is associated with the microbial limestone facies of the earliest Triassic of South China. The newly reported fauna is well preserved and extraordinarily rich (30 benthic macroinvertebrate species, including the new species Astartella? stefaniae (Bivalvia) and Eucochlis obliquecostata (Gastropoda)) and stems from an environmentally stable setting providing favourable conditions for benthic organisms. Whereas changes in the taxonomic composition are negligible over the observed time interval of 10-100ka, three ecological stages are identified, in which relative abundances of initially rare species continuously increased at the cost of previously dominant species. Concomitant with the changes of dominant species is an increase in faunal evenness and heterogeneity. In the absence of both environmental and taxonomic changes, we attribute this pattern to the long-term effects of interspecific competition, which acted at an unusually slow pace because the number of competing species and potential immigrants was dramatically reduced by the end-Permian mass extinction. We suggest that these non-actualistic conditions led to decreased rates of niche differentiation and hence to the delayed rediversification of benthos that characterizes the aftermath of the greatest Phanerozoic mass extinction event. A hyperbolic diversification model is proposed, which accounts for the positive relationship between the intensity of interspecific competition and the rate of niche differentiation and resolves the conundrum of delayed rediversification at a time when niche space was largely vacated.
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