Download Mass Extinctions

Lecture 29: Mass Extinctions
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Phanerozoic Mass Extinctions
Mississippian
Pennsylvanian
Jurassic
Cambrian
Ma
Apparent percentage of marine animals going extinct
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C
P
D
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Magnitude (biodiversity loss during extinction event)
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Intensity (duration of extinction event)
Measure of extinction event
Ordovician Mass Extinction(s)
• Global cooling and widespread glaciers in southern continents
• Global sea level drops – continental shelves exposed
• Third largest Phanerozoic extinction event - 60% of marine invertebrates wiped out
Devonian Mass Extinction(s)
354
Hangenberg
Event
Kellwasser
Event
416
Causes:
* Rapid, multiple pulses of transgressions/regression
* Widespread oceanic anoxia
* Bolide impact?
Results: 22% of all families, 57% of genera and 75% of species extinct
Mississippian Extinction
Causes:
* Global cooling and south polar glaciation
Results - Seventh largest mass extinction of the Phanerozoic Era:
* Numerous brachiopod genera extinct globally, many others locally. Nearshore
genera suffered very slightly higher rates of extinction.
* Extinction did not select against genera because of their environmental breadth,
number of regional occurrences (a proxy for relative abundance), species diversity, or
body size.
• Extinction did strongly select against genera with narrow global latitudinal ranges.
* Genera that survived late Mississippian mass extinction dominate global brachiopod
faunas until the middle Permian.
Pennsylvanian Extinction
Causes - Within a few thousand years:
* Global temperatures become cooler and drier
* Intense ice age and global sea level fall (300 ft.)
* End-Carboniferous global warming
Results:
* Coal forest devastation – Once cosmopolitan ecosystem fragmented into smaller
“islands”; cannot adapt to quickly increasing temperatures.
* Vertebrate and invertebrate groups tied to coal forests die out – includes many
amphibian groups and large insect species
* Reptiles fare well – remember the amniote egg!
Permian Mass Extinction
Mississippian/Pennsylvanian
mass extinctions:
•Glaciation at southern pole – less
water in ocean basins
•Uplift – increased sediment supply
•Pangea forms – less coastal area
Permian mass extinction:
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Miss./Penn. causes, +
Siberian Traps
Bolide?
Methane traps?
• The most devastating of all mass extinctions. Nearly 96% of all
marine and terrestrial species went extinct. Very rapid!
• In the sea rugose and tabulate corals, trilobites, many classes,
orders and families of crinoids, brachiopods, ammonoids, as well as
other echinoderm, mollusk, and vertebrate taxa went extinct.
• On land a total breakdown of terrestrial ecosystems occurred. Most
vertebrate and plant groups went extinct.
• The Earth came close to a pre-Ediacaran (Late Proterozoic) state –
i.e., being nearly devoid of multicellular animal and plant life.
• Cause(s) of the extinction are not totally known, but may include
rapid global warming, anoxic oceans, widespread volcanism,
methane gas release, and/or extraterrestrial impact.
Following the Permian mass extinction:
* Triassic terrestrial and marine ecosystems devastated.
* Soil formation was halted on land, seas were anoxic.
* Land and seas populated by very few species – surviving species
dominate ecosystems (low diversity but high abundance).
* Triassic recovery from the mass extinction took nearly 6 Ma.
Triassic Mass Extinction
Causes:
Bolide? No Triassic-Jurassic impact crater identified
Gradual climate change or sea level fluctuations? To sudden…
Massive volcanic activity? Massive volumes of basaltic magma
extruded (CAMP). Paleosols preserve huge spike in CO2, HS2,
aerosols – would cause intense global warming or global cooling
Biocalcification crisis? Organisms unable to utilize CaCO3
Results:
20% of all marine families extinct (conodonts gone)
At least 50% of all known species extinct (i.e., non-crocodile
crurotarsans, some therapsids, many large amphibians)
Extinction of groups of large reptiles allows for eventual
dominance of dinosaurs during Jurassic Period
Jurassic Extinction
Causes:
Unknown…
Results: “Minor” mass extinction, including most stegosaurids and sauropods,
many genera of ammonoids, marine reptiles, and bivalves
extinct
Cretaceous Mass Extinction
Causes:
* Asteroid impacts (Wetumpka, Manson, esp. Chicxulub)
* Massive volcanic activity (Deccan Traps) – huge volumes of basaltic magma
extruded, noxious gases released into atmosphere
* Net effect is reduced sunlight and photosynthesis – collapse of food chain
* Gradual sea level and climate changes? Evidence for end-Cretaceous cooling global
temperatures…
Results of Cretaceous Mass Extinction
Extinction of:
• Non-avian dinosaurs
• Mosasaurs
• Ammonites
• Pterosaurs
Significant fuanal turnover of:
• Ostracodes
• Coccolithophores
• Radiolarians
• Foraminifera
• Terrestrial plants
• Mollusks
extinct
Survivors - the more generalized, the better:
• 80% of cartilaginous fish
• 90% of bony fish
• Turtles
• Crocodilians
• Avian dinosaurs
• Squamate lizards
• Mammals