Lecture 29: Mass Extinctions

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Phanerozoic Mass Extinctionsb

iod

ivers

ity

Mississippian

Pennsylvanian

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Jurassic

Cambrian

Apparent percentage of marine animals going extinct

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P

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Magnitude (biodiversity loss during extinction event)X

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

Causes:* Rapid, multiple pulses of transgressions/regression

* Widespread oceanic anoxia

* Bolide impact?

Kellwasser Event

Hangenberg Event

416

354

Devonian Mass Extinction(s)

Results: 22% of all families, 57% of genera and 75% of species extinct

Mississippian Extinction

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.

Causes:

* Global cooling and south polar glaciation

Pennsylvanian Extinction

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!

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

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:

•Miss./Penn. causes, +•Siberian Traps•Bolide?•Methane traps?

Permian Mass Extinction

• 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.

* 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.

Following the Permian mass extinction:

Triassic Mass Extinction

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

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

Jurassic Extinction

Results: “Minor” mass extinction, including most stegosaurids and sauropods, many genera of ammonoids, marine reptiles, and bivalves

Causes: Unknown…

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…

Extinction of:•Non-avian dinosaurs•Mosasaurs•Ammonites•Pterosaurs

Survivors - the more generalized, the better:•80% of cartilaginous fish•90% of bony fish•Turtles•Crocodilians•Avian dinosaurs•Squamate lizards•Mammals

Significant fuanal turnover of:•Ostracodes•Coccolithophores•Radiolarians•Foraminifera•Terrestrial plants•Mollusks

Results of Cretaceous Mass Extinction

extinct