Early Cretaceous record of microboring organisms in skeletons of growing corals

Abstract

A spectacularly preserved assemblage of microbial euendoliths, penetrating into skeletons of growing scleractinian corals, has been recognized in Early Aptian (Early Cretaceous) reef limestone of the Rarǎu Mountains (East Carpathians, NE Romania). Microboring euendolithic filaments were found in five coral colonies of the suborder Microsolenina. They remained in part well-preserved, often impregnated with iron oxides, which made them visible even in strongly recrystallized parts of coral skeletons. Filaments of a wide range of sizes (2-40μm in diameter) were concentrated within medium parts of coral septa, oriented along the septa in the direction of the coral growth. The larger filaments were tubular, occurring in bundles and branched into finer, often tapering branches. Their behaviour and organization were quite similar to the modern euendolithic siphonalean chlorophyte Ostreobium. Filament diameters exceeded those reported for the modern species, but covered a similarly wide size range. Narrower frequently branching filaments, 4-8μm in diameter, resemble distal branching patterns of modern Ostreobium quekettii. Some very thin filaments (ca. 1-2μm) observed within skeleton or inside the large tubular filaments, sometimes associated with globular swellings, may represent euendolithic fungi. The recrystallization of coral skeleton had limited effect on preservation of euendoliths due to their impregnation with iron oxides; microbial euendoliths were subjected to different taphonomic changes. □Chlorophytes, Early Cretaceous, fungi, microbial euendoliths, Romania, scleractinian corals. © 2011 The Authors, Lethaia © 2011 The Lethaia Foundation.