Reconstructing a Carboniferous inferred coral–alcyonarian association using a biomineralogical approach

Abstract

The taxonomic assignation and ecological implications of the genus Syringoalcyon Termier & Termier, 1945 have been a palaeontological problem for a long time. Carboniferous material from Morocco and Spain has been studied using a biomineralogical approach by means of petrographic microscopy, SEM, AFM, EMPA and CIP microscopy analysis. Detailed morphological, structural, chemical composition and crystallographic data enable a deeper understanding of the nature of Syringoalcyon. The coral walls and the so‐called epithecal scales exhibit conspicuous differences in microstructure (lamellae and holacanthine fibres in the coral vs. single crystal in scales), nanostructure (pill‐shaped vs. granule‐shaped nanocrystals), composition (LMC vs. HMC) and crystallographic orientation. The results of these analyses imply that Syringoalcyon is an association between the tabulate coral Syringopora and an epibiont. They also suggest that the epibiont was an alcyonarian (a rare occurrence in the fossil record) that was attached to the syringoporoid. This work highlights the utility of the biomineralizational approaches for solving palaeontological problems, such as systematic affinities, and for advancing knowledge of the evolution of biocrystallization processes.

Alcyonacea awakens: Palaeobiology and palaeoecology of Palaeozoic octocorals known from their sclerites

“…Some features indicate that the growth process could be quite similar in Palaeozoic sclerites. Thus, the occurrence of a step located at the base of the spindle sclerites (Figures a and a,b) and the concentric growth of the sclerite around the insertion area (Coronado et al, ) indicate a first stage, when the sclerite grows out the cellule, and a second stage of maturation ( sensu Jeng et al, ), which occurs once the sclerite is inserted into the wall.…”

“…To date, Termieralcyon has only been recorded through sclerites that are thought to be the hard tissue of the skeleton of an Alcyonacea (Coronado et al, ). The genus Syringoalcyon Termier & Termier, is not valid for these sclerites, as this taxon comprises both the syringoporoid substrate and the epibiont sclerites, and, thus, the description of the genus and of the different species created to date is mainly based on features of the syringoporoid rather than on characteristics of the sclerites.…”

“…Coronado et al () provided petrographic and palaeontological evidence that indicate the occurrence of a former soft tissue associated with the sclerites. This evidence includes the occurrence of Thartharella isp.…”

“…Coronado, Fernández‐Martínez, Rodríguez, and Tourneur () performed a complete analysis of diverse material assigned to Syringoalcyon using optical petrography, scanning electron microscopy (SEM), atomic force microscopy (AFM), electron microprobe analysis (EMPA), and computer‐integrated polarization (CIP). According to these authors, the interpretation of Young and Noble () and Tourneur et al () is correct, with the scales being generated by an epibiont.…”

“…This paper refers to the study performed by Coronado et al () and embraces a systematic, palaeobiological, and palaeobiogeographical study of the coral–alcyonacean association known as Syringoalcyon . During this research, we found numerous sclerites in rocks bearing syringoporoid corals from 15 new Carboniferous outcrops (located in Morocco, Algeria, Spain, Iran, China, USA, and Mexico; see Table ).…”