A new genus of Rhynchonellid Brachiopod from the Lower Triassic of South China and Implications for timing the recovery of Brachiopoda after the end-Permian mass extinction

A new genus, Meishanorhynchia, is proposed based on new material from the Lower Triassic of the Meishan section, South China. It is of a late Griesbachian age based on both associated biozones (ammonoids and
bivalves) and radiometric dates of the intercalated volcanic ash beds. Comparison with both Palaeozoic and Mesozoic-Cenozoic-related genera suggests that it may represent the first radiation of progenitor brachiopods in the aftermath of the end-Permian extinction. The lowest brachiopod horizon that contains the genus is estimated to be about 250.1±0.3 Ma. This implies that the initial stage of recovery of Brachiopoda in the Early Triassic was probably about 1.3±0.3 myr after the major pulse of the end-Permian mass extinction (dated as 251.4±0.3 Ma). This is in agreement with Hallam's expectancy that biotic recovery typically begins within one million years or so of major mass extinctions, in contrast to current views on the end-Permian extinction event which propose that the recovery of most if not all biotic groups in the Early Triassic was severely delayed and only began about five million years after the end-Permian extinction.

End-Permian mass extinction pattern in the northern peri-Gondwanan region

The Permian-Triassic extinction pattern in the peri-Gondwanan region is documented biostratigraphically, geochemically and sedimentologically based on three marine sequences deposited in southern Tibet and comparisons with the sections in the Salt Range, Pakistan and Kashmir. Results of biostratigraphical ranges for the marine faunas reveal an end-Permian event comparable in timing with that known at the Meishan section in low palaeolatitude as well as Spitsbergen and East Greenland in northern Boreal settings although biotic patterns earlier in the Permian vary. The previously interpreted delayed extinction (Late Griesbachian) at the Selong Xishan section is not supported by our analysis. The end-Permian event exhibits an abrupt marine faunal shift slightly beneath the Permian-Triassic boundary (PTB) from benthic taxa- to nektic taxa-dominated communities. The climate along the continental margin of Neo-Tethys was cold before the extinction event. However, a rapid climatic warming event as indicated by the southward invasion of abundant warm-water conodonts, warm-water brachiopods, calcareous sponges, and gastropods was associated with the extinction event. Stable isotopic values of δ13Ccarb, δ13Corg and δ18O show a sharp negative drop slightly before and during the extinction interval. Sedimentological and microstratigraphical analysis reveals a Late Permian regression, as marked by a Caliche Bed at the Selong Xishan section and the micaceous siltstone in the topmost part of the Qubuerga Formation at the Qubu and Tulong sections. The regression was immediately followed by a rapid transgression beneath the PTB. The basal Triassic rocks fine upward, and are dominated by dolomitic packstone/wackestone containing pyritic cubes, bioturbation and numerous tiny foraminifers, suggesting that the studied sections were deposited during the initial stage of the transgression and hence may not have been deeply affected by the anoxic event that is widely believed to characterise the zenith of the transgression.

Controls on body size during the Late Permian mass extinction event

This study examines the morphological responses of Late Permian brachiopods to environmental changes. Quantitative analysis of body size data from Permian–Triassic brachiopods has demonstrated significant, directional changes in body size before, during and after the Late Permian mass extinction event. Brachiopod size significantly reduced before and during the extinction interval, increased for a short time in more extinction-resistant taxa in the latter stages of extinction and then dramatically reduced again across the Permian ⁄ Triassic boundary. Relative abundances of trace elements and acritarchs demonstrate that the body size reductions which happened before, during and after extinction were driven by primary productivity collapse, whereas declining oxygen levels had less effect. An episode of size increase in two of the more extinction-resistant brachiopod species is unrelated to environmental change and possibly was the result of reduced interspecific competition for resources following the extinction of competitors. Based on the results of this study, predictions can be made for the possible responses of modern benthos to present-day environmental changes.

Systematics and palaeoecology of Changhsingian (Late Permian) Ambocoeliidae brachiopods from South China and implications for the end-Permian mass extinction

Four Ambocoeliidae brachiopod species including one new species (Crurithyris tazawai sp. nov., Crurithyris sp., Paracrurithyris pygmaea and Attenuatella mengi) are described from the Changhsingian (Late Permian) deep-water facies of South China. Analysis of the morphology, palaeoecology and palaeogeographical and temporal distributions of these species revealed that the presence of a delthyrium and/or the micro-ornaments among three of the four species (Crurithyris tazawai sp. nov., Paracrurithyris pygmaea and Attenuatella mengi) favoured an epifaunal (epiphytic) lifestyle. Morphological differences suggest that Paracrurithyris pygmaea may have been more effective metabolically in forming the shell compared with Attenuatella mengi and Crurithyris tazawai. The temporal and palaeogeographical distribution of Attenuatella suggests that A. mengi inhabited cool or cold deep waters. Both Crurithyris tazawai and Attenuatella mengi disappeared earlier in the stratigraphic record than Paracrurithyis pygmaea during the Permian–Triassic mass extinction. These differences in timing of extinction, morphology and palaeogeographical distributions suggest that oxygen deficiency and trophic resource limitation (a consequence of the changing composition of marine phytoplankton in the seas) may have contributed to the end-Permian mass extinction.

Significant pre-mass extinction animal body-size changes : evidences from the Permian–Triassic boundary brachiopod faunas of South China

This paper has undertaken a quantitative and statistical analysis of brachiopod body-size changes through the marine Permian–Triassic boundary section at Zhongzhai, Guizhou Province, South China, and found that (1) pre-mass extinction dwarfing is evident for at least the rugosochonetid species chosen for this study; (2) Tethyochonetes species reduced their size earlier than that in the Neochonetes species; and (3) no significant size reduction occurred in the newly evolved species of these two genera. Inter-species competition for resources between Neochonetes species and Tethyochonetes species and the reduction of food supply in the upper part of the uppermost Permian is here proposed to explain these observed stratigraphic patterns of brachiopod body-size changes throughout the Zhongzhai section. In the case of the newly evolved species showing no significant body-size change, morphological innovations (adaptations) in the process of speciation are considered to have significantly enhanced these newly evolved species' flexibility and survival in coping with degrading environmental conditions.

Sedimentology and ichnology of two lower Triassic sections in South China: implications for the biotic recovery following the end-Permian mass extinction

Biotic recovery following the end-Permian mass extinction was investigated using trace fossil and facies analysis of two Lower–Middle Triassic sections in South China. The Susong section (Lower Yangtze Sedimentary Province) comprises a range of carbonate and mudstone facies that record overall shallowing from offshore to intertidal settings. The Tianshengqiao section (Upper Yangtze Sedimentary Province) consists of mixed carbonate and siliciclastic facies deposited in shallow marine to offshore settings. Griesbachian to Dienerian ichnological records in both sections are characterized by low ichnodiversity, low ichnofabric indices (1–2) and low bedding plane bioturbation indices (1–2). Higher ichnofabric indices (3 and 4), corresponding to a dense population of diminutive ichnotaxon, in the Tianshengqiao section suggest opportunistic infaunal biotic activity during the earliest Triassic. Ichnological data from the Susong section show an increase in ichnodiversity during the late Smithian with 11 ichnogenera identified and increased ichnofabric indices of 4–5 and bedding plane bioturbation indices of 3–5. Although complex traces such as Rhizocorallium are present in Spathian-aged strata in this section, low ichnodiversity and ichnofabric indices and diminutive Planolites suggest a decline in recovery. In the Tianshengqiao section, ichnofabric indices are moderate to high (3–5) although only six ichnogenera are present and Planolites burrows are consistently small in Smithian and Spathian strata. Complex traces, such as large Rhizocorallium and Thalassinoides, and large Planolites, did not appear until the Anisian. Ichnological results from both sections record the response of organisms to unfavourable environmental conditions although the Susong section shows earlier recovery during the Smithian prior to latest Smithian–Spathian decline. This decline may have resulted from a resurgence of euxinic to anoxic marine environment in various regions of South China. Ichnological data from the Tianshengqiao section indicate protracted recovery throughout the Early Triassic as previously found elsewhere in South China. Comparison of the South China trace fossil records with global ichnological data show a diachronous pattern of recovery of trace makers and highlights the heterogeneous development of oxic facies on the marked variation in recovery rate.

Proliferation of MISS-related microbial mats following the end-Permian mass extinction in the northern Paleo-Tethys: evidence from southern Qilianshan region, western China

As a consequence of the end-Permian mass extinction, microbes proliferated in the post-extinction shallow marine ecosystems, in which they grew as various microbially induced sedimentary structures (MISSs) in siliciclastic settings. This paper reports, for the first time, the discovery of abundant MISSs from the lowest Triassic sandstones of shallow-water margin origin in the Zhihema sections of the southern Qilianshan region, West China. The sandstones are characterized by well-developed cross-beddings and ripple marks, and a Claraia-dominated bivalve assemblage of middle-late Griesbachian age. These sedimentary structures, together with the bivalves, suggest a high-energy peritidal zone of a shoreface setting in a clastic shallow sea environment. Seven types of MISSs are recognized and described here: pictograph-like sand cracks/crack-fills, polygonal sand crack-fills, erosional remnants, multidirectional linear grooves, sinuous crack-fills, fusiform sand cracks/crack-fills, and leveled ripple marks. Most of the newly found MISSs are morphologically comparable with their ancient and modern counterparts. Detailed optical microscope and scanning electron microscope (SEM) analyses reveal that thin clayey laminae and filamentous mica grains are aligned parallel to bedding plane, and that the matrix-supported quartz grains, overall, are oriented; both of which are interpreted to indicate biogenic origin. The biogenic origin of these MISSs is reinforced by the presence of copious putative nanoglobules and filamentous biofilm-like organic objects in the interspaces of clay minerals in laminated layers. These nanometer-scale objects are interpreted as bacterial bodies or remains that have been replaced with inorganic minerals upon fossilization. The presence of MISSs on the northern margins of Paleo-Tethys indicates that the post-extinction microbial mats had expanded their distributions from low-latitude to moderate-high latitude regions. Moreover, unlike some previously reported microbial mats that contain very rare body and trace fossils, the southern Qilianshan MISSs were found in association with abundant vertical burrows and bivalves, suggesting that the MISS-forming microbial mats may have served as oases for trace-making organisms and opportunistic bivalves to flourish in shallow-marine habitats immediately after the end-Permian mass extinction.

Post-extinction brachiopod faunas from the late Permian Wuchiapingian coal series of South China

This paper describes fourteen brachiopod species in eleven genera from the Late Permian Wuchiapingian Coal Series (Lungtan Formation) of South China. Of these, the shell bed fauna from the basal Lungtan Formation is interpreted to represent the onset of the recovery of shelly faunas in the aftermath of the Guadalupian/Lopingian (G/L) mass extinction in South China. The post-extinction brachiopod faunas in the Wuchiapingian are characterized by the presence of numerous Lazarus taxa, survivors, and newly originating taxa. These elements capable of adapting their life habits were relatively more resistant to the G/L crisis. The post-extinction faunas, including survivors and the elements originating in the recovery period, have no life habit preference, but they were all adapted to a variety of newly vacated niches in the Late Permian oceans. Two new species, Meekella beipeiensis and Niutoushania chongqingensis, are described, and two Chinese genera, Niutoushania and Chengxianoproductus, are emended based on re-examination of the type specimens and new topotype materials from the Lungtan Formation.

Permophricodothyris pavlova, 1965 (Brachiopoda, Spiriferida) from the Permian of South China: its morphology, biostratigraphy and distribution

A study of both silicified and nonsilicified specimens of Permian reticularioid brachiopods from South China suggests that Permophricodothyris, a genus previously rarely reported from China, is actually very common and abundant in the Middle and especially Upper Permian of South China. This study also clarifies, for the first time, that many of the reticularioid brachiopod species previously described as Squamularia in fact belong to Permophricodothyris. The new data presented in this paper also allows a critical evaluation of Permophricodothyris in relation to its closest allies: Phricodothyris, Squamularia, Bullarina and Neophricodothyris. The revision reveals that a total of 18 Permophricodothyris species are present in the Middle and Upper Permian of South China, with only one species, P. squamularioides, having survived the Permian-Triassic mass extinction. Two species, P. grandis (Chao) and P. guangxiensis Han, Zhou & Wang, are redescribed here, providing critical new information on the morphology and taxonomy of these species.

Global review of permian Tyloplecta muir-wood and cooper, 1960 (Brachiopoda): morphology, palaeobiogeographical and palaeogeographical implications

A global review of the stratigraphical and geographical distribution of Tyloplecta reveals that the genus ranges in age from Kungurian to Changhsingian (Middle to Late Permian). Tyloplecta first evolved in South China in the Kungurian (late Early Permian). The genus went through its first diversification in the Guadalupian, suffered a major extinction at the end of the Guadalupian, and re-diversified in the Wuchiapingian. T. yangtzeensis persisted into the Changhsingian as the only survivor of the genus involved in the end-Permian mass extinction. Palaeogeographically, South China is not only the centre of origin for the genus but also an area of diversification and evolution. In addition to South China, Tyloplecta has also been recorded from the Far East Russia, Japan, central Thailand, Laos, Cambodia, Qiangtang Terrane of Tibet, Salt Range, Iran, Armenia, Hungary, Yugoslavia, and Slovenia. This geographic spread suggests that Tyloplecta was primarily restricted to the Palaeotethys and is indicative of warm-water palaeoequatorial conditions. Its presence in some of the northeast Asian terranes (e.g., parts of Japan and Far East Russia) and in the Salt Range (Pakistan) and central and north Iran (part of the Cimmerian microcontinents) demonstrate that the genus invaded the middle palaeolatitudinal regions in both hemispheres during the late Middle Permian in response to increased shallow marine biotic communications between Cathaysia in the eastern Palaeotethys and southern Angaraland, and between Cathaysia and Peri-Gondwanaland. The invasion of Tyloplecta (and some other taxa) into the southern shore waters of Angaraland may be explained by assuming ocean surface current connections and close palaeogeographical proximities between the South China, Sino-Korea and Bureya blocks. In comparison, the invasion of Tyloplecta into the Peri-Gondwanaland region is more likely a result of reduced palaeogeographical distance between South China and Peri-Gondwanaland and the appearance of the Cimmerian microcontinents as migratory stepping stones.