Topic 7.1: Permian-Triassic Extinction

When was the Permian-Triassic extinction?

252 million years ago, end of Paleozoic era, beginning of Mesozoic era

marine invertebrate affectations

heavy losses, esp. groups with calcium-carbonate exoskeletons.

brachiopods and crinoids (marine invertebrates)

major reduction in diversity

marine invertebrates completely lost

rugose & tabulate corals, goniatitic ammonoids, eurypterids, trilobites

terrestrial invertebrate affectations

largest extinction of insects

terrestrial vertebrate affectations

2/3 loss of labyrinthodont amphibians, sauropsids, and therapsids

large herbivores suffered the most

demise of almost all anapsids

terrestrial plant affectations

loss of forests, major changes in ecosystem architecture

how long did it take for terrestrial vertebrate fauna to recover?

30 million years

factors of P-T extinction

LIPS, Siberian Trap volcanism, basalt flows, rapid global warming, ocean acidification/anoxia, volcanic darkness/cooling/photosynthetic shutdown

lower Triassic offshore settings

life high in water column, above deep, anoxic sea floor. shrimp, ammonoids, thylacocephalans

lower Triassic shallow marine settings

abundant microbially-induced sedimentary structures, bivalves, lingulide brachiopods, low diversity trace fossil associations

marine refugia

delta-front regions, narrow zone above storm-wave base, high diversity assemblages in isolated zones

who survived easiest?

mobile carnivores and detritivores

survival mechanisms

innovations in behaviour, concentration in refugia, global reduction in endemism and concomitant increase in forms with cosmopolitan distribution, shift from equatorial/tropical areas to higher latitudes

reducing body size helps, mobility helps

marine mesozoic revolution

rapid diversification of durophagus and terebrophagus organisms (shell crushers/drillers), arthropods, return of large body sizes

middle/upper Triassic crinoids

decimated at the end of Permian, only 2 lineages survived. experienced rapid diversification through Triassic, pushed into deeper water (still associated with reefs)

scleratinian

coral type, appeared in Mid-Triassic and rapidly spread/diversified

upper triassic offshore settings

monotypic assemblages of pectinate bivalves. sea floor recovery did not occur during Triassic

lower Triassic patterns in diversity

diverse fish, free-swimming arthropods, dysoxia-tolerant bivalves, arthropod-dominated refugia near deltas, common organic mats in shallow water settings

middle Triassic patterns in diversity

diverse/abundant shallow marine assemblages, resurgence of Paleozoic fauna (brachiopods/crinoids), low diversity and population density in offshore settings

upper Triassic patterns in diversity

return of true coral reefs, Paleozoic-style coasts with strong modern overprint (brachiopods diminish, bivalves more common), offshore settings dominated by monotypic bivalves, most life up in water column