Effect of Posterior Gut Reduction on the Evolution of Rhynchonelliform Brachiopods

Brachiopods are a group of animals that are known since the Early Cambrian, and thrived in the Paleozoic. After the Permian–Triassic extinction, there was a significant reduction in the taxonomic diversity of brachiopods. According to one hypothesis, in the Mesozoic, brachiopods with a blind gut could not restore their former numbers due to the predominance of shelled plankton. We assume that the terebratulids, the most widespread group of recent brachiopods, were able to adapt to the changed diet due to the more efficient filtration mechanism of the plectolophous lophophore. Extant rhynchonellids have a blind–ending bulbous end of the digestive tract, which is probably used for crushing and digesting hard-shelled plankton.