Burrowing sculptures and life habits in Paleozoic lingulacean brachiopods

A range of specialized burrowing sculptures evolved convergently in at least one lingulid and in several obolid and lingulasmatid genera. The sculptures in Lingula punctata (Ordovician) indicate a burrowing process with the pedicle trailing behind the shell, similar to that of Recent Lingulidae. In the Obolidae and Lingulasmatidae, the orientation of the sculptures indicates a burrowing process with the pedicle oriented downward in the sediment. A burrowing mechanism in which the valves alternated in functioning as anchors, without active participation of the pedicle, is proposed for these forms. Infaunal life habits for several obolid genera are further indicated by the shell morphology and by the distribution of repaired shell damage. The burrowing Obolidae are likely to have been adapted to relatively high-energy environments, which required frequent reburrowing in addition to escape (upward) burrowing. The increase in bioturbation in these environments in the Middle Paleozoic may have contributed to their extinction. The Lingulidae, instead, being mostly adapted to extreme environmental conditions, could survive in marginal niches which were not intensively exploited by actively burrowing organisms