Benthic Paleoecology and Macroevolution During the Norian Stage of the Late Triassic

Shallow marine benthic animals underwent major paleoecological changes during the Norian Stage of the Late Triassic. This research identified these biological transitions by collecting several thousand macroinvertebrate fossils from sedimentary sequences representing two major oceanic realms in the Triassic: the Tethys Sea and Panthalassa. The faunal turnovers were correlated with a combination of chronostratigraphic methods, including strontium isotope chemostratigraphy. Among shelly invertebrates, stationary surface-dwellers that were ecologically dominant in the Early Norian were replaced in multiple phases by animals that were facultatively mobile, or capable of burrowing into the sediment, or cemented to the seafloor. These transitions coincided with taxonomic radiations of predators that were specialized for durophagy in shallow marine environments. The synchronous appearance of morphological features and behaviors related to benthic durophagy among multiple clades of predators and prey suggest the Norian Stage was a non-static interval in which evolutionary and geological forcers operated at a global scale to reorganize shallow marine ecosystems.