Earliest Wuchiapingian (Lopingian, Late Permian) brachiopods in southern Hunan, South China : implications for the Pre-Lopingian crisis and onset of Lopingian recovery / radiation

The uppermost 5-15 m of the Douling Formation in the southern Hunan area. South China, yields a diverse fauna comprised of ammonoids, bivalves, and brachiopods. The brachiopods reported in this paper consist of 51 species in 34 genera and are dominated by the Lopingian (Late Permian) species associated with a few species persisting from the underlying Maokouan (Late Guadalupian). This fauna is of earliest Wuchiapingian in age as precisely constrained by the associated conodont Clarkina postbitteri postbitteri and the Guadalupian-type ammonoid fauna of the Roadoceras-Doulingoceras Zone in the brachiopod horizon. The discovery of the Lopingian species-dominated brachiopod fauna in the earliest Wuchiapingian in southern Hunan suggests a much less pronounced effect of the pre-Lopingian crisis (end-Guadalupian mass extinction) than the end-Changhsingian mass extinction in terms of brachiopods, a contemporaneous onset of the Lopingian recovery/radiation during the pre-Lopingian crisis period, and taxonomic selectivity of the pre-Lopingian crisis in terms of different fossil groups. New taxa are Echinauris doulingensis n. sp., Pararigbyella quadrilobata n. gen. and n. sp. and P. doulingensis n. gen. and n. sp.

Late Permian marine ecosystem collapse began in deeper waters: Evidence from brachiopod diversity and body size changes

Analysis of Permian-Triassic brachiopod diversity and body size changes from different water depths spanning the continental shelf to basinal facies in South China provides insights into the process of environmental deterioration. Comparison of the temporal changes of brachiopod diversity between deepwater and shallow-water facies demonstrates that deepwater brachiopods disappeared earlier than shallow-water brachiopods. This indicates that high environmental stress commenced first in deepwater settings and later extended to shallow waters. This environmental stress is attributed to major volcanic eruptions, which first led to formation of a stratified ocean and a chemocline in the outer shelf and deeper water environments, causing the disappearance of deep marine benthos including brachiopods. The chemocline then rapidly migrated upward and extended to shallow waters, causing widespread mass extinction of shallow marine benthos. We predict that the spatial and temporal patterns of earlier onset of disappearance/extinction and ecological crisis in deeper water ecosystems will be recorded during other episodes of rapid global warming.

Recovery pattern of brachiopods after the Permian-Triassic crisis in South China

In South China, the Changhsingian brachiopods are extraordinarily abundant and diverse, comprising 468 species in 144 genera. However, approximately 91% of brachiopod species were eliminated during the Permian-Triassic (P-Tr) mass extinction event. Brachiopods in the aftermath of the P-Tr mass extinction were extremely rare, with only one opportunistic taxon, Lingulida, occasionally found in the Griesbachian and Smithian at a high abundance. Species-diversity of articulated brachiopods in the early Griesbachian, late Griesbachian, Dienerian, and Smithian are 35, 3, 2, and 0, respectively. Although a few of Mesozoic-type species occurred in the Griesbachian, Dienerian and Smithian, a marked diversification of brachiopods occurred in the Spathian and early Anisian and was characterised by 9 and 17 Mesozoic-type species, respectively. The diversification of brachiopods in the Spathian and early Anisian coincides with the contemporaneous expansion of the refuge zone, suggesting that the improvement of marine environmental conditions (e.g., lethally hot temperature and anoxic seawater) played a key role in brachiopod recovery after the P-Tr mass extinction.

A new Changhsingian (Late Permian) brachiopod fauna from the Zhongzhai section (South China) Part 3: Productida

Zhang, Y., He, W.H., Shi, G.R., Zhang, K.X. & Wu, H.T., 26.2.2015. A new Changhsingian (Late Permian) brachiopod fauna from the Zhongzhai section (South China) Part 3: Productida. Alcheringa 39, xxx–xxx. ISSN 0311-5518. As the third and last part of a systematic palaeontological study of the brachiopod fauna from the Permian–Triassic boundary section at Zhongzhai in Guizhou Province (South China), this paper reports 15 species (including three new species: Tethyochonetes minor sp. nov., Neochonetes (Zhongyingia) transversa sp. nov., Paryphella acutula sp. nov.) in Order Productida. In addition, the morphological features and definitions of several key Changhsingian brachiopod taxa (e.g., Paryphella and Oldhamina interrupta) are clarified and revised.

Nearshore-offshore-basin species diversity and body size variation patterns in Late Permian (Changhsingian) brachiopods

 B.V. Body size is a fundamental and defining character of an organism, and its variation in space and time is generally considered to be a function of its biology and interactions with its living environment. A great deal of body size related ecological and evolutionary research has been undertaken, mostly in relation to extant animals. Among the many body size-related hypotheses proposed and tested, the size-bathymetry relationship is probably the least studied. In this study, we compiled a global body size dataset of Changhsingian (Late Permian, ca. 254. Ma-252. Ma) brachiopod species from low-latitude areas (30°S-30°N) and analyzed their species diversity and body size distribution patterns in relation to the nearshore-offshore-basin bathymetric gradient. The dataset contained 1768 brachiopod specimens in 435 species referred to 159 genera and 9 orders, from 135 occurrences (localities) of 18 different palaeogeographic regions. Treating the whole of the Changhsingian Stage as a single time slice, we divided the nearshore-offshore-basin bathymetric gradient into three broad depth-related environments: nearshore, offshore and basinal environments, and compared how the species diversity and body size varied along this large-scale bathymetric gradient.Here, we report an array of complex patterns. First, we found a clear overall inverse correlation between species diversity and water depth along the nearshore-offshore-basin gradient, with most species concentrating in the nearshore environment. Second, when the median sizes of all low-latitude brachiopod species from the three environments were compared, we found that there was no significant size difference between the nearshore and offshore environments, suggesting that neither the wave base nor the hydrostatic pressure exerts a critical influence on the body size of brachiopods. On the other hand, the median sizes of brachiopods from the nearshore environment and, to a lesser extent, the offshore environment were found to be significantly larger than that of basinal brachiopods. This trend of significant size reduction in basinal brachiopods mirrors the relative low species diversity in the basinal environment, and neither can be easily explained by the tendency of decreasing food availability towards deeper sea environments. Rather, both trends are consistent with the hypothesis of an expanding Oxygen Minimum Zone (OMZ) in the bathyal (slope to deepsea) environments, where hypoxic to anoxic conditions are considered to have severely restricted the diversification of benthos and favored the relative proliferation of small-sized brachiopods. Finally, a significant difference was also found between eurybathic and stenobathic species in their body size response to the nearshore-offshore-basin gradient, in that eurybathic species (species found in all three environments) did not tend to change their body size significantly according to depth, whereas stenobathic forms (species restricted to a single environment) exhibit a decline in body size towards the basinal environment. This pattern is interpreted to suggest that bathymetrically more tolerant species are less sensitive to depth control with respect to their body size change dynamics, in contrast to stenobathic species which tend to grow larger in shallower water depths.

Fluctuations of redox conditions across the Permian–Triassic boundary : new evidence from the GSSP section in Meishan of South China

Oceanic anoxia has long been considered as one of the main causes for the end-Permian mass extinction. However, the results obtained by different researchers are rather divergent from different sections, or even on the same section using the same redox proxy. This study aims to examine the causes for some of these divergent results using high-resolution pyrite framboid sampling at the Meishan GSSP section in South China. Detailed microfacies analysis shows that the uppermost Late Permian strata comprises two significantly different sedimentary facies: one characterized by silicious muddy limestone and recognized as representing autochthonous background sediments; the other distinguished by bioclastic grainstone, interpreted to be allochthonous in origin and have been transported from the nearby platform margin. These two different sedimentary facies represent two distinctly different redox conditions. Together with the facies analysis, a statistical analysis of pyrite framboids was carried out to evaluate the redox evolution across the Permian-Triassic boundary. Abundant framboids with average diameters of about 6μm are found in background sediments beneath the extinction boundary, indicating generally anoxic bottom water conditions. But this condition was punctuated by transient intervals of rapid oxygenation interpreted to have been caused by intrusion of intermittent turbidity flows. Our study also showed that anoxic conditions persisted into the immediate aftermath of the mass extinction, thereafter it was quickly followed by a relatively long period of oxic conditions (with rare framboids). However, the redox conditions returned to anoxia (with abundant pyrite framboids averaging about 5μm in diameter), accompanied by a rapid global transgression. The oxygenation manifested near the Permian-Triassic boundary coincides with the negative excursion of carbon isotope. This would imply that, contrary to previous interpretations, this great δ13C negative excursion was probably not caused by the upwelling of anoxic deep ocean waters.

Global brachiopod palaeobiogeographical evolution from Changhsingian (Late Permian) to Rhaetian (Late Triassic)

Previous studies suggest that the end-Permian mass extinction caused a dramatic drop of marine biodiversity near the Permian-Triassic boundary. However, it is unclear how profoundly this severe extinction might have changed the global provincialism, and how global provincialism responded to the protracted process of this extinction and subsequent recovery through the Triassic. In this paper, we carried out quantitative time-series analyses of global brachiopod palaeobiogeography over a timespan of nine consecutive stages/substages from the latest Permian Changhsingian to the latest Triassic Rhaetian based on a global brachiopod database of 483 genera and 2459 species from 1425 localities. Our results suggest that the extinction resulted in a global 'biogeographical eclipse' in the ensuing Early Triassic Griesbachian and Dienerian times in that neither biogeographic realm nor province could be recognized. It was characterized by an extreme low-diversity, mostly dwarfed and nearly globally distributed brachiopod fauna, coupled with persistently high sea surface temperature and a flattened global latitudinal thermal gradient. Global provincialization emerged again during the Olenekian at province level and reached its peak stage during the Carnian when three realms and six provinces were clearly recognized. Global provincialism became weakened again in the latest Triassic Rhaetian, marked by three general realms, but no province distinguished. Our analyses suggest that both palaeolatitude-related thermal gradient and the presence of Pangea (a profound geographic barrier) were most effective in explaining the spatial patterns. In addition, oceanic currents along the northwestern coast of Pangea also played an important (albeit regional) role in linking southern North and Central America brachiopod faunas with those of the Boreal Realm. This study also revealed that the brachiopod biodiversity center moved northwards over the studied interval, accompanied and hence accountable for by the northward drift of a large number of tectonic blocks in the Palaeotethys and Neotethys during the Triassic.

Patterns of brachiopod faunal and body-size changes across the Permian-Triassic boundary: Evidence from the Daoduishan section in Meishan area, South China

New analysis of Permian-Triassic brachiopod assemblages and body-size changes in South China provides insights into the process of the environmental crisis in the lead up to the end-Permian mass extinction. The recently discovered Daoduishan section of South China can be considered as an important auxiliary section for the study of brachiopods at the Meishan Section D of South China, the GSSP of the Permian-Triassic Boundary (PTB). This paper studied changes of the brachiopod assemblages and body sizes through the upper part of the Changxing Formation and basal Yinkeng Formation of Daoduishan. The results show that significant changes of brachiopod assemblages took place between Beds 24e and 26. Brachiopods?Prelissorhynchia sp. and Paracruirithyris pygmaea are the dominators in Beds 14-24e, while Tethyochonetes pigmaea and Paryphella spp. are the dominators in Beds 26-29. Body sizes of brachiopods significantly decreased between Beds 24e and 26 and then maintained smaller means in Beds 27-29. Studies of brachiopod morphological features indicate both Tethyochonetes and Paryphella had advantageous adaptations enabling them to copy with living in an anoxic/dysoxic and/or low-productivity environment during the Permian-Triassic crisis.

An index for defaunation

Defaunation, originally conceived as the loss of large vertebrates due to hunting or fragmentation, has been widely used in conservation studies yet the term has been arbitrarily used and poorly defined. Here we refine this term by creating a quantitative index that can be used to compare ecological communities over large zoogeographical regions. We propose a defaunation index (. D) as a weighted measure of dissimilarity between the current assemblage of a given location and a reference assemblage that represents a historical and/or unperturbed state. We analyzed the index by means of three case studies that included two empirical assessments of mammal communities in Neotropical rainforests and one hypothetical example, encompassing a variety of criteria to quantify differences in species density and importance. These cases illustrate the broad range of index applicability and show that incorporating functional differences among species, such as those based on body size, conservation status or evolutionary originality can add important information beyond simply species richness. © 2013 Elsevier Ltd.

Defaunation in the Anthropocene

Conselho Nacional de Desenvolvimento Científico e Tecnológico (CNPq)

Geochronological constraints on the age of a Permo-Triassic impact event: U-Pb and Ar-40/Ar-39 results for the 40 km Araguainha structure of central Brazil

Impact cratering has been a fundamental geological process in Earth history with major ramifications for the biosphere. The complexity of shocked and melted rocks within impact structures presents difficulties for accurate and precise radiogenic isotope age determination, hampering the assessment of the effects of an individual event in the geological record. We demonstrate the utility of a multi-chronometer approach in our study of samples from the 40 km diameter Araguainha impact structure of central Brazil. Samples of uplifted basement granite display abundant evidence of shock deformation, but U/Pb ages of shocked zircons and the Ar-40/Ar-39 ages of feldspar from the granite largely preserve the igneous crystallization and cooling history. Mixed results are obtained from in situ Ar-40/Ar-39 spot analyses of shocked igneous biotites in the granite, with deformation along kink-bands resulting in highly localized, partial resetting in these grains. Likewise, spot analyses of perlitic glass from pseudotachylitic breccia samples reflect a combination of argon inheritance from wall rock material, the age of the glass itself, and post-impact devitrification. The timing of crater formation is better assessed using samples of impact-generated melt rock where isotopic resetting is associated with textural evidence of melting and in situ crystallization. Granular aggregates of neocrystallized zircon form a cluster of ten U-Pb ages that yield a "Concordia" age of 247.8 +/- 3.8 Ma. The possibility of Pb loss from this population suggests that this is a minimum age for the impact event. The best evidence for the age of the impact comes from the U-Th-Pb dating of neocrystallized monazite and Ar-40/Ar-39 step heating of three separate populations of post-impact, inclusion-rich quartz grains that are derived from the infill of miarolitic cavities. The Pb-206/U-238 age of 254.5 +/- 3.2 Ma (2 sigma error) and Pb-208/Th-232 age of 255.2 +/- 4.8 Ma (2 sigma error) of monazite, together with the inverse, 18 point isochron age of 254 +/- 10 Ma (MSWD = 0.52) for the inclusion-rich quartz grains yield a weighted mean age of 254.7 +/- 2.5 Ma (0.99%, 2 sigma error) for the impact event. The age of the Araguainha crater overlaps with the timing of the Permo-Triassic boundary, within error, but the calculated energy released by the Araguainha impact is insufficient to be a direct cause of the global mass extinction. However, the regional effects of the Araguainha impact event in the Parana-Karoo Basin may have been substantial. (C) 2012 Elsevier Ltd. All rights reserved.

From Amazonia to the Atlantic forest: Molecular phylogeny of Phyzelaphryninae frogs reveals unexpected diversity and a striking biogeographic pattern emphasizing conservation challenges

Documenting the Neotropical amphibian diversity has become a major challenge facing the threat of global climate change and the pace of environmental alteration. Recent molecular phylogenetic studies have revealed that the actual number of species in South American tropical forests is largely underestimated, but also that many lineages are millions of years old. The genera Phyzelaphryne (1 sp.) and Adelophryne (6 spp.), which compose the subfamily Phyzelaphryninae, include poorly documented, secretive, and minute frogs with an unusual distribution pattern that encompasses the biotic disjunction between Amazonia and the Atlantic forest. We generated >5.8 kb sequence data from six markers for all seven nominal species of the subfamily as well as for newly discovered populations in order to (1) test the monophyly of Phyzelaphryninae, Adelophryne and Phyzelaphryne, (2) estimate species diversity within the subfamily, and (3) investigate their historical biogeography and diversification. Phylogenetic reconstruction confirmed the monophyly of each group and revealed deep subdivisions within Adelophryne and Phyzelaphryne, with three major clades in Adelophryne located in northern Amazonia, northern Atlantic forest and southern Atlantic forest. Our results suggest that the actual number of species in Phyzelaphryninae is, at least, twice the currently recognized species diversity, with almost every geographically isolated population representing an anciently divergent candidate species. Such results highlight the challenges for conservation, especially in the northern Atlantic forest where it is still degraded at a fast pace. Molecular dating revealed that Phyzelaphryninae originated in Amazonia and dispersed during early Miocene to the Atlantic forest. The two Atlantic forest clades of Adelophryne started to diversify some 7 Ma minimum, while the northern Amazonian Adelophryne diversified much earlier, some 13 Ma minimum. This striking biogeographic pattern coincides with major events that have shaped the face of the South American continent, as we know it today. (C) 2012 Elsevier Inc. All rights reserved.

Biological evolution of replicator systems: towards a quantitative approach

The aim of this work is to study the features of a simple replicator chemical model of the relation between kinetic stability and entropy production under the action of external perturbations. We quantitatively explore the different paths leading to evolution in a toy model where two independent replicators compete for the same substrate. To do that, the same scenario described originally by Pross (J Phys Org Chem 17:312–316, 2004) is revised and new criteria to define the kinetic stability are proposed. Our results suggest that fast replicator populations are continually favored by the effects of strong stochastic environmental fluctuations capable to determine the global population, the former assumed to be the only acting evolution force. We demonstrate that the process is continually driven by strong perturbations only, and that population crashes may be useful proxies for these catastrophic environmental fluctuations. As expected, such behavior is particularly enhanced under very large scale perturbations, suggesting a likely dynamical footprint in the recovery patterns of new species after mass extinction events in the Earth’s geological past. Furthermore, the hypothesis that natural selection always favors the faster processes may give theoretical support to different studies that claim the applicability of maximum principles like the Maximum Metabolic Flux (MMF) or Maximum Entropy Productions Principle (MEPP), seen as the main goal of biological evolution.

Patterns of the Remnant Cichlid Fauna in Southern Lake Victoria. Patrones de la Fauna de Ciclidos Remanentes en el Sur del Lago Victoria

During the years 1984–1987 Lake Victoria in East Africa experienced what is probably the largest mass extinction of contemporary vertebrates. Within a decade about 200 endemic species of haplochromine cichlids disappeared. The extinctions that occurred in the 1980s have been documented predominantly on species of offshore and sub-littoral waters in the Mwanza Gulf of southern Lake Victoria. Although the littoral fauna of southern Lake Victoria had not been examined in detail, their diversity seemed less affected by the changes in the ecosystem. We give results of the first comprehensive inventory of the littoral cichlid fauna in southern Lake Victoria and discuss its conservation status. We also report on new developments in the sub-littoral fauna after 1990. More than 50 littoral and 15 sub-littoral stations were sampled between the years 1991 to 1995. Of the littoral stations, 34 were sampled for the first time. One hundred sixty three species of haplochromines were collected. Of these, 102 species were previously unknown. About two thirds of them live in rocky areas that were sampled for the first time. Littoral rocky habitats harbored the highest diversity. Since 1990, however, 13 more species disappeared from established sampling stations in littoral habitats. Fishing practices, spreading of exotic fishes, water hyacinth, and eutrophication are considered important threats to the littoral fauna. Also in the upper sub-littoral the number of species declined further. On deeper sub-littoral mud bottoms individual and species numbers increased again, although they are nowhere close to those found before the Nile perch (Lates niloticus) upsurge. This fauna differs from the well studied pre-Nile perch fauna. At well-established sampling stations, the sub-littoral zone is dominated by previously unknown species, and some known species have performed dramatic habitat shifts.