Lecture 13: The Great Dying Flashcards
How long is the boundary between the paleozoic & the mesozoic AND the permian and the triassic?
254.1 Ma
As we leave the permain species diversity and community complexity…
After the extinction event…
reached the most diverse communities ever existed
that kind of diversity would not be reached again until many millions of years later (until the cretaceous, 125 million years later)
Fossil record in triassic compared with permian?
Very few fossils are found, and of those very low diversity on land & sea.
Life had been decimated by the late Permian extinction…
50% of marine families, ~90% of species lost
even worse on land: ~75% of families, 95% species lost
As a consequence of this extinction event , the nature of the early Triassic record is quite different from that which proceeds it.
Certain things don’t occur in the geological cycle…
No coral reef for about 7 8 My as we cross this boundary.
‘chert’ gap for same time.
‘coal’ gap (no coals being deposited) for about 10my
Where is a global P/Tr reference section?
Meishan, China
Groups lost during the great extinction…
Groups lost: 100% blastoid echinoderms 100% rugose corals 100% tabulate corals 100% acanthodian fish and… 100% trilobites 100% eurypterids …but both had already dramatically declined before P/Tr
Marine sediments say…global ocean anoxia
In the deep sea, limestones and red cherts disappear
replaced by black mudstones
boundary sediments rich in Corg and pyrite (FeS2): indicators of anoxia
extreme anoxia (euxinia) extended into Photic zone: biomarkers for photosynthetic sulphur bacteria
Benthos decimated by low bottom H2O oxygen levels (part of reason for extinction).
Isotope excursions in marine and terrestrial successions
δ18O shows global temperature rise of 6 ºC
δ13C drops: too big to represent just a drop in global primary productivity? Something else must be driving it as well.
The marine realm was very hostile…
Sustained late Permian stratified ocean with upper euxinic layer (precipitating iron sulphide in the water column)
Hot and acid seas present before the isotope excursions
Oceans 15 °C at poles - warm deep polar water
Reduced pole-equator temperature gradient
The terrestrial biota is more than decimated…
Only mass extinction to significantly affect insects
Gymnosperm-dominated Glossopteris floras disappeared
2/3 of amphibians, reptiles and mammal-like reptiles lost
Top predators (gorgonopsians) died out
most large vertebrates disappeared
What terrestrial sediments say…
Coals disappear
Green Permian mudstones replaced by Triassic sands/conglomerates
Slow deposition by meandering rivers Switches to rapid deposition by braided rivers
Soils indicate high temperatures & low oxygen conditions at high latitudes
Evidence for rapid soil erosion
Welcome to the ‘boring’ Early Triassic…
After extinction event: Marine
From high diversity, complex Permian seas to low diversity Triassic faunas
Populated globally by 4 ubiquitous genera….
Claraia (a ‘paper’ scallop) : the most cosmopolitan bivalve fauna ever
All dysaerobic (low O2) taxa
Dicynodonts here, there and everywhere
Lystrosaurus dominates earliest Triassic land faunas: up to 90%
A cosmopolitan post-extinction disaster species
A world dominated by herds of a slow plant-grubbing herbivores
Other dicynodont survivors
small, heavily built, barrel chested, short internal nostrils
all adaptations for burrowing in dry, dusty, arid environments
tusks for grubbing (cf., the Siberian Marmot)
the new Triassic species developed an upright gait
