Recovery of brachiopods after the Permian–Triassic mass extinction: diversity, ornamental evolution, and paleobiogeography
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Abstract:
The Brachiopoda is one of the most important components in the Paleozoic benthic community. During the Permian-Triassic (P-Tr) mass extinction, many orders of this phylum were wiped out. Brachiopods became a marginal group in the Mesozoic and Cenozoic oceans. To investigate the effects of the P–Tr extinction on the macroevolution of this clade, we re-evaluated the diversity variations of global brachiopods during the Triassic, traced the evolutionary trend of the development of ornamentation of the Triassic and Early Jurassic elements, and analyzed the changes of brachiopod paleobiogeographic provincialisms before and after the extinction. Taxonomic diversity at the genus level abruptly declined across the P–Tr crisis, increased rapidly in the Anisian, and finally reached the highest level of the Triassic during the Norian. Compared with genera that originated in the Late Triassic, those originated in the Early Triassic are shorter in longevity. The novel ornamentation index was employed to evaluate the development of the ornamentation of brachiopods. The results show that the four main orders of the early Mesozoic brachiopods behaved differently in ornamental evolution, suggesting that their ornamental trajectories were not controlled by a common factor. Compared with the escalation-driven evolution, their evolutionary history played a more important role. The ornamentation development shows no significant relationship with the strengthened predation pressure, at least during the early Mesozoic. Network analysis indicates that the paleobiogeographic provincialism disappeared after the extinction, and re-emerged in the Olenekian. Along with the occurrence of many endemic elements during the Middle Triassic, the affinities of brachiopod faunas became much lower among various regions in the world.
