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The Cambrian cnidarian Cambroctoconus orientalis occurs in clusters exhibiting pendent growth in crypts within thrombolite frameworks. Here we successfully reconstruct its three‐dimensional (3D) in situ mode of life. The 3D reconstruction shows the initial individuals of colonies and attachment structures, budding sites and growth modes of coralla in response to the extent of sheltered spaces. The earliest individuals were attached to the framework by a suction‐cup‐like structure and were basically orthogonal to the walls, growing downward. Their calicular bases were pierced by a hole. Individuals were initially cylindrical and gradually formed an octagonal column during growth. Budding occurred everywhere, and toroidal budding traces are abundant upon the corallite surfaces. The attachment structures were secondarily reinforced by continuous secretion from the coenenchymal tissue. Offsets continued to grow only when sufficient growth space was available, while producing as many individuals as possible. Growth of individuals was commonly halted by the surrounding framework. Growth directions were in part modified by corallite curvature to avoid collisions between corallites and to make full use of the intricate void spaces. In deteriorating conditions, offset corallites appeared through regeneration rather than budding from the remaining soft tissues. Active exploitation of the sheltered spaces within thrombolites, which remained dominant during the Cambrian, was thus conducted by C. orientalis. Notably, the cryptobionts treated herein adopted subtle growth strategies that have not previously been fully understood and are not easily interpreted with reference to organisms living in open spaces. [ABSTRACT FROM AUTHOR]

Adachi, N., Ezaki, Y. & Liu, J. 2011: The oldest bryozoan reefs: a unique Early Ordovician skeletal framework construction. Lethaia, Vol. 45, pp. 14-23. The oldest bryozoan reefs occur in the Lower Ordovician (late Tremadocian) Fenhsiang Formation of the Three Gorges area, South China. These reefs show a unique type of bryozoan ( Nekhorosheviella) framework, and were constructed as follows: the first stage involved colonization by lithistid sponges, which acted as a baffler to trap sediments, providing bryozoans with a stable substrate for attachment. The bryozoans then grew as an encruser on the surfaces of sponges, showing a preferential downwards and lateral growth within the sponge scaffolding to avoid biological and physical disturbance. Finally, these biotic combinations among skeletal organisms formed a rigid, three-dimensional skeletal framework. This mode of bryozoan growth in association with lithistid sponges is remarkable and unique in its growth direction, and the appearance of such reefs, just prior to the widespread development of skeletal-dominated reefs as part of the Great Ordovician Biodiversification Event, provides an excellent example of the earliest attempts by skeletal organisms to form frameworks by themselves. This find significantly enhances our understanding of the initial stages of skeletal-dominated reef evolution and the ensuing development of reefs during the Middle-Late Ordovician. □ Bryozoa, Early Ordovician, lithistid sponge, Ordovician radiation, reef. [ABSTRACT FROM AUTHOR]

The framework-building stromatoporoid Stachyodes, the encrusting calcimicrobe Rothpletzella and encrusting Graticula-like red algae are major contributors to red algal–calcimicrobial–stromatoporoid bindstones in the Lower Devonian Elmside Formation of the Yass Basin, New South Wales, Australia. The distribution and accumulation patterns of encrusting organisms within the red algal–calcimicrobial–stromatoporoid bindstones observed by optical microscopy and SEM imply a biotic interrelationship between skeletal organisms and microbes that reflects environmental changes. Rothpletzella is characterized by prostrate filaments with frequent branching and a high angle of bifurcation. Filaments of Graticula-like red algae exhibit rare branching and a relatively low angle of bifurcation. In addition, they are prostrate at the base before becoming erect. Both Rothpletzella and the red algae successively encrust the surfaces of skeletal frameworks, but exhibit different distributions. Rothpletzella and other calcimicrobes cover both the lower and upper surfaces of frameworks, whereas red algae are limited to the upper surfaces. Their individual distributions are thus significantly influenced by the frameworks formed by the thin, laminar stromatoporoid Stachyodes, which create different microenvironments as by-products. The limited distribution of the red algae was probably related to light levels or phototropism. Upper framework surfaces are variously encrusted by calcimicrobes and the red algae to form thick crusts with varying accumulation patterns. Micritization around the algal thalli, covering of calcimicrobes such as Wetheredella, and microbial micrites between algal thalli all suggest interruptions of algal growth that correspond to episodes of harsh environmental conditions. Transitions from Graticula-like red algae to Rothpletzella reflect periods of deteriorating environmental change for skeletal organisms, which resulted in the predominance of microbial growth. In contrast, a resurgence of red algae on calcimicrobes suggests improved environmental change. Repeated accumulation patterns between Graticula-like red algae and Rothpletzella indicate changing habitat environments and competitive relations within skeletal organisms and microbes. These relationships provide insight into understanding how skeletal organisms and microbes utilized space and how they interrelated with each other to produce Devonian reefal limestones. [ABSTRACT FROM AUTHOR]