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The polychaete borings Caulostrepsis taeniola, Caulostrepsis cretacea, Caulostrepsis avipes, Caulostrepsis penicillus isp. nov., Maeandropolydora elegans, Maeandropolydora sulcans, Sulcichnus sigillum, the bryozoan boring Pinaceocladichnus onubensis and the phoronid boring Talpina cf. hackberryensis occur in coralla of the solitary scleractinian coral Ceratotrochus (Edwardsotrochus) duodecimcostatus in the upper Pliocene middle/lower neritic to upper bathyal fine-grained deposits of NE Tunisia. This very rich assemblage of borings is produced in vivo as suggested by (i) their occurrence close to the surface and mostly in the upper part of coralla (Caulostrepsis ispp., M. elegans), even if they are known to penetrate deeply in the substrate, or (ii) evidence of corallum deformation in response to the boring action (Sulcichnus sulcans). The remaining borings were probably produced post mortem; they penetrate deeply into the corallum (M. sulcans) or always occur shallowly in the substrate (Talpina) and, in addition, cross cut other borings (Pinaceocladichnus). The polychaete borings are dominant. The abundance of the borings is probably caused by ecological pressure from shallower zones in subtropical waters. This resulted in the colonization of hard, small-sized substrates located in relatively deep (offshore) waters. The interpretation of age and palaeoenvironment was elucidated by the analysis of benthic and planktonic foraminifers. [ABSTRACT FROM AUTHOR]

The coral microbiome comprises skeleton-associated microendoliths (boring algae, bacteria and fungi) which are important for coral health and reef conditions. The analysis of microborings is a key tool in deciphering of the skeletal microbiome of fossil corals. Even micrometre-size traces have a high preservation potential and indicate the trace-maker organisms that inhabited skeletons of live corals. SEM studies of resin replicas and naturally occurring internal moulds of microborings were performed on skeletons of Jurassic, Cretaceous, Palaeogene, and Miocene colonial corals. This study and a literature review show that microborings (mostly 2–10 μm in diameter) which were formed in coral skeletons during their lifetimes are common in some fossil corals. They are ubiquitous throughout the whole colony, concentrated in the inner part of skeletal elements, and located commonly roughly along their longitudinal axis, in the direction of the coral growth. Post-mortem microborings, occurring at the margin of the skeletal elements, were rare in the examined samples. The coral-associated microendoliths were like in modern reef corals, mainly represented by Ostreobium quekettii or similar green algae, and less commonly by red algae, cyanobacteria, and fungi. Analyses of microborings can be also applied in studies of the skeleton microbiome of modern living corals. [ABSTRACT FROM AUTHOR]

Eocene–Oligocene reefs have been reported in Europe largely from the circum‐Mediterranean region. In this paper, small coral reefs from the northwestern Transylvanian Basin (Romania) are described for the first time. They developed near the Eocene–Oligocene boundary, most probably during the Priabonian, and belong to northernmost outposts of the reef belt developed during this time in Europe. The studied sedimentary successions in Letca and Băbeni–Cuciulat (Sălaj County), up to 55 m thick, belong to the Cozla Formation. The reefs occur within a shallow‐water succession composed mostly of bedded limestones, dominated by bioclastic (coralline) packstones. Low‐relief (constratal) reefs, locally up to 10–15 m in thickness, are spaced cluster (matrix‐supported) reefs. Scleractinian corals are common but poorly diversified (10 species and 8 genera). Branching ramose colonies, branching low‐integrated phaceloid, and sheet‐like (foliaceous) corals dominate. Neither lateral zonation nor vertical succession of reefs was recognized. Corals co‐occur with encrusting and geniculate red algae, but they are of subordinate significance for a nonrigid reef framework. Branching corals baffled or trapped suspended carbonate mud that contributed to the reef growth and ongoing development of topographic relief. Associated fossils are of low to moderate diversity. A relatively low‐energy environment, moderate to high sedimentation rate, and increased turbidity are inferred from carbonate muddy and fine‐grained matrix, dominance of sediment‐resistant corals, their morphology, common occurrence in growth position, as well as low to moderate degree of bioerosion and encrustation. Transylvanian reefs in terms of poor coral diversity, matrix‐supported texture, and turbid‐water sedimentary setting show similarities with many coeval reefs from the circum‐Tethyan area. [ABSTRACT FROM AUTHOR]