Article: Stromatoporoid palaeobiology and taphonomy in a Silurian biostrome on Gotland, Sweden

A well-exposed stromatoporoid biostrome in the Hemse Group (middle Ludlow) of Gotland, Sweden, displays a wide range of stromatoporoid morphologies distributed amongst 16 species. The most abundant species, Clathrodictyon mohicanum Nestor has a laminar to low domical form, often of large size, distributed throughout the biostrome. Fast lateral growth is suggested to account for its abundance and commonly large size, its profile being suited to the normally low to moderate energy environment envisaged for the biostrome. Several other species adopted a similar growth style but were less successful; yet others, such as Plectostroma intermedium Yavorskyi, show a range of growth form from low to high domical shape, suggesting a phenotypic plasticity of growth form of each of these species. However, the range simply reflects the fact that individuals grew taller with age. Most laminar to low domical stromatoporoids at Kuppen are intact, but taller forms were frequently damaged and overturned by periodic storm action, indicating that a lower profile was clearly an advantage. Some species show variations in distribution of undamaged forms horizontally between, and vertically within, localities; there is evidence that some responded to environmental gradients, notably turbulence and sedimentation. Most grew on a stable substrate provided by dead skeletons of other stromatoporoids. Under cathodoluminescence stromatoporoid skeletons show speckled dull and bright luminescence, an identical signal to the pelmatozoan debris found in the biostrome, circumstantial evidence for an original mineralogy of high Mg calcite in both.