Revision of Middle Devonian stromatoporoid Climacostroma from South China

Abstract

ClimacostromaYang and Dong, 1979, an endemic stromatoporoid genus, originally discovered in central Guangxi, South China, has remained enigmatic for over 40 years. Its validity and systematic position in the Order Stromatoporida (hypercalcified sponges) is here reinterpreted. In this study, the original collections of Climacostroma (including holotypes of C. guangxiense, C. microlaminatum and C. facetum) by Yang and Dong (1979) were re-examined, with improved images of the internal skeletons. We show that this genus is diagnostically characterized by thin microlaminae, dominant cassiculate structures between microlaminae, and distinct acosmoreticular to orthoreticular microstructures. Prior studies revealed similarities of Climacostroma with Stromatopora, Lineastroma, Ferestromatopora, Arctostroma, Habrostroma, and Parallelostroma. However, Climacostroma is markedly different from Stromatopora and Lineastroma by possessing thin microlaminae and microreticulate microstructure. Climacostroma is distinguished from Ferestromatopora and Arctostroma by the lack of dominant oblique or arched structures. Habrostroma differs from Climacostroma by the absence of prominent cassiculate structures. We found that Parallelostroma is most similar to Climacostroma in having dominant cassiculate structures between microlaminae and orthoreticular microstructure. Thus, we propose that Climacostroma is combined with Parallelostroma, and is reclassified under the Family Parallelostromatidae of the Order Syringostromatida, instead of its current position in the Family Stromatoporidae of the Order Stromatoporida. The three original species are here revised as two valid species, namely, P. guangxiense and P. microlaminatum.