Microbialite masses within the lowest Triassic strata along the southern periphery of the tropical Yangtze Platform were produced in a post-Permian microbial regime. These microbialites (the Hindeodus parvus Zone), which are represented by thrombolites, occur only where terrigenous sediment influx was rare, even in shallow-marine settings. The lower parts of the thrombolites lie upon a distinctly unconformable Permian-Triassic boundary and exhibit a thinbedded to thick-bedded planar structure. In contrast, the upper parts of the thrombolites contain domed macrostructures that interact in complex ways with skeletal grainstones and packstones. Irregular frameworks of thrombolite bodies differ in degree of lateral and vertical accumulation and in the amalgamation of mesoclots of microbial origin; they exhibit marked variations in texture. A transgressive episode occurred in the earliest Triassic following the mass extinctions, and this included the initiation of microbial regimes that usually formed planar thrombolite masses in lower-energy, deep subtidal environments. The varied textures and structures of thrombolites during deposition may reflect a combination of sea-level fluctuations, physicochemical ocean conditions, microbial activity, skeletalsediment influx, and other factors. These earliest Triassic, uniquely microbial regimes collapsed in stepwise fashion and were succeeded by the Isarcicella staeschei and I. isarcica zones, which contain a predominance of mudstones, suggesting a marked sea-level transgression. Space-specific and time-specific, the earliest Triassic microbialites record short-term, high-resolution paleoenvironmental fluctuations immediately after the end-Permian extinctions.

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The Ordovician is a period when novel reef ecosystems appeared along with new reef constructors and skeletal-dominated reefs. The Lower Ordovician (late Tremadocian) Fenhsiang Formation of the Three Gorges area in South China contains the oldest known bryozoan reefs (lithistid sponge-bryozoan and bryozoan-pelmatozoan reefs) alongside lithistid sponge-microbial reefs. The latter are characterized by the dominance of microbialites that encrusted and bound the frame-building sponges and inter-sponge sediments. In contrast, the lithistid sponge-bryozoan and bryozoan-pelmatozoan reefs are generally characterized by bryozoans that encrusted the frame-building sponges or pelmatozoans and grew to fill the inter-frameworks. These sponges and pelmatozoans did not construct the rigid frameworks unaided; their association with bryozoans enabled the development of small skeletal-dominated reefs with rigid frameworks. Skeletal-dominated reefs, for which frame-constructing and encrusting roles are conspicuous, were largely unknown before the Early Ordovician. The appearance of skeletal organisms (specifically colonial, encrusting bryozoans) enabled the development of skeletal-dominated reefs, which were pioneers in the rise of Middle-Late Ordovician reefs. The Early Ordovician establishment of skeletal-dominated reefs at the earliest stages of the Great Ordovician Biodiversification Event would have created novel niches and biological interactions that further promoted the evolution of reef-building and -dwelling organisms, as well as ensuing reef ecosystems.

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ABSTRACT. Scleractinian corals are the most important constituents of modern coralgal reefs. For many years, it was thought that they first appeared in the Middle Triassic and subsequently underwent explosive radiation. However, abundant scleractinian-like corals with ancestral morphological traits have recently been recovered from Middle Permian sponge reefs in China, which not only confirms a role in Permian reef ecology but also suggests a possible Palaeozoic origin for the group. Two species of a new Permian scleractiniamorph genus from China are described herein as Houchangocyathus wangi gen. et sp. nov. and Houchangocyathus yaoi gen. et sp. nov.Putative Palaeozoic Scleractinia may have evolved over a substantial time interval and diverged into stem lineages by the end of the Permian. These forms evolved within both the rigid framework of their basic body plan and the morphological constraints characteristic of each lineage. The Middle Permian development of calcisponge reefs was closely related to habitat expansion, which would have provided an ideal dwelling for scleractinian-like corals and enhanced their chances of fossilization. Such scleractiniamorphs disappeared at the end-Permian extinction, but may have survived as progenitors of Triassic Scleractinia.

Sessile organisms are influenced considerably by their substrate conditions, and their adaptive strategies are key to understanding their morphologic evolution and traits of life history. The family Flabellidae (Cnidaria: Scleractinia) is composed of the representative azooxanthellate solitary corals that live on both soft and hard substrates using various adaptive strategies. We reconstructed the phylogenetic tree and ancestral character states of this family from the mitochondrial 16S and nuclear 28S ribosomal DNA sequences of ten flabellids aiming to infer the evolution of their adaptive strategies. The Javania lineage branched off first and adapted to hard substrates by using a tectura-reinforced base. The extant free-living flabellids, including Flabellum and Truncatoflabellum, invaded soft substrates and acquired the flabellate corallum morphology of their common ancestor, followed by a remarkable radiation with the exploitation of adaptive strategies, such as external soft tissue [e.g. Flabellum (Ulocyathus)], thecal edge spine, and transverse division (e.g. Placotrochus and Truncatoflabellum). Subsequently, the free-living ancestors of two genera (Rhizotrochus and Monomyces) invaded hard substrates independently by exploiting distinct attachment apparatuses such as tube-like and massive rootlets, respectively. In conclusion, flabellids developed various morphology and life-history traits according to the differences in substrate conditions during the course of their evolution.

Asexual reproduction is one of the most important traits in the evolutionary history of corals. No real-time observations of asexual reproduction in azooxanthellate solitary scleractinian corals have been conducted to date. Here, we describe previously unknown aspects of asexual reproduction by using Truncatoflabellum spheniscus (Family Flabellidae) based on observations of transverse division conducted over 1200 days. The findings revealed that (1) transverse division was caused by decalcification; (2) compared to the anthocyathus (upper part of the divided corallum), the soft parts of the anthocaulus (lower part of the divided corallum) were severely damaged and injured during division; (3) these injuries were repaired rapidly; and (4) the anthocaulus regrew and repeatedly produced anthocyathi by means of transverse division. Differences in the patterns of soft-part regeneration and repair, as well as differences in skeletal growth rates between the anthocaulus and the anthocyathus imply that the ecological requirements and reproductive success are different from each other immediately after division. The findings provide important clues for unravelling why asexual reproduction appeared frequently in free-living corals, and the extent to which those modes of reproduction has affected the adaptive and evolutionary success of scleractinian corals throughout the Phanerozoic.