Abstract
An assemblage of dome-shaped calcified fossils was discovered in resedimented deposits of the Monte Facito Formation (Middle Triassic, Ladinian) of the Southern Apennines, Italy. The fossils occur within a mass-transport deposit and are interpreted as having originated in a shallow-marine carbonate environment prior to downslope redeposition. In outcrop, they resemble stromatoporoids or calcareous algae and may have contributed to carbonate substrate development. The fossils consist of successive carbonate laminae separated by micritic to fine-grained carbonate layers. Internally, they display a porous fabric but lack chambers and diagnostic skeletal structures typical of stromatoporoids, other hypercalcified sponges, corals, or calcareous algae. Both the skeletal framework and part of the interlaminar carbonate have undergone extensive neomorphism. Energy Dispersive Spectroscopy analyses indicate a predominantly carbonate composition, whereas the interlaminar material contains Al and Si, suggesting a siliciclastic component. Cathodoluminescence analyses provided no significant additional information. Microbial crusts and possible bioerosional borings locally truncate both skeletal laminae and encrusting microbial fabrics. These features suggest post-mortem colonization by boring organisms, possibly including endolithic sponges, indicating prolonged exposure of the fossils on the seafloor before burial. The affinity of these enigmatic fossils remains unresolved, with hypercalcified sponges and calcareous algae representing the most plausible alternatives. Nevertheless, the associated microbial and bioerosional features indicate participation in a complex microbial/metazoan community that contributed to carbonate substrate production and ecological recovery during the rebuilding of shallow-marine ecosystems following the end-Permian mass extinction.