The composition of the Tethyan plankton in the Triassic

Triassic plankton already resembled modern communities to a considerable degree. After the end-Permian extinction, primary producers rebounded quickly: acritarchs and prasinophytes dominate Early Triassic successions, and the first calcareous nannoliths, including true coccoliths, appear by the late Norian to Rhaetian in the western Tethys and British Columbia. Calcispheres may record encysting algae, while oberhauserellid foraminifers are considered precursors of planktonic globigerinids. Unambiguous dinoflagellate cysts emerge in Middle Triassic strata of Western Australia.

Zooplankton diversified at the same pace. Radiolarians regained pre-extinction richness by the Anisian and Ladinian, with spectacular faunas in the Buchenstein Formation of the Dolomites. Planktonic crinoids, documented by masses of micro-ossicles from the Cassian Formation, formed a conspicuous suspension-feeding tier. Meroplankton was equally abundant: protoconchs show that most Cassian gastropods produced planktotrophic larvae, and echinoderms with similar larval strategies (holothurians, echinoids, ophiuroids) are widespread from Ladinian time onward, even though pluteus or auricularia ossicles are only sporadically preserved. Throughout the period, prolific ammonite populations imply a constant flux of cephalopod paralarvae that nourished higher trophic levels.

Far from being radiolarian-only, Triassic plankton already contained most of the elements that later structured Mesozoic, and ultimately modern, marine food webs.