BIOL 2040 Lecture Notes - Lecture 19: Survivorship Curve, Neontology, Background Extinction Rate
27 Apr 2018
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Lecture 19 - Fossils and Extinction
April 11, 2018
10:51 PM
Orientation to the Fossil Record
• First billion years
o When life emerged
o Only need to remember three dates:
• 541 Mya - Cambrian radiation
• 250 Mya - End-Permian mass extinction
• 65 Mya - Dinosaur extinction
• 2 biggest trends
o End-Permian mass extinction
• The largest mass extinction
o Dinosaur mass extinction
Paleozoic
• 540 Mya - Cambrian radiation (radiation of animal phyla)
o Colonization of land begins soon after - insects, land plants, tetrapods
• First mammal-like animals appeared
• 251 Mya - Permian mass extinction
• There was a major change in animal life between Paleozoic and Mesozoic
Mesozoic
• Dinosaurs don't emerge until after the Permian era
• Cretaceous era - diversity of dinosaurs at its maximum
• Warm climate allows land plants to diversify
Cenozoic (Tertiary/Paleogene/Neogene)
• Emergence of different lineages of mammals
• After 65 Mya (mass extinction of dinosaurs)
• End-Cenozoic - cyclical ice age, world-wide
Extinction
• The two extinction events are important (250 Mya - End-Permian mass extinction, 65 Mya -
Dinosaur mass extinction) to life on earth
Survivorship Curves
• Background extinction
• There are 3 survivor ship curves
o In regards to percentage still alive
o If you watch an individual from birth to death, their survivorship curve will be 1 of the 3
curves
find more resources at oneclass.com
find more resources at oneclass.com
o Linear - probability of species becoming extinct is the same regardless of age
Background Extinction
• It is the standard rate of extinction, the normal extinction rate
• Species (not individuals) have the same likelihood to die regardless of age
• Species don't necessarily "age", get old, and die
o Aging is based on independent individuals
o Probability of extinction is independent of species age - a species that appeared 50 Mya has
the same probability of dying as a species that appeared 30 Mya in terms of 'age'
• Extinctions are not uniform in time
o The likelihood of a species going extinct is not the same over 20 Mya
Mass Extinctions
• The big five:
find more resources at oneclass.com
find more resources at oneclass.com
o Ordovician
o Devonian
o Permian
o Triassic
o Cretaceous
• We only focus on Permian (End-Permian, 540 Mya) and Cretaceous (End-Cretaceous, 65 Mya -
Dinosaur) mass extinctions
o It divides the biggest chunks in fossil records
• Most complete evidence is from marine species
• There is increasing evidence for land animals and plants that they participated in extinction
Fossil Record Gaps and Biases
• Very few individuals leave fossils
• Over-represented
o Hard Parts
• Bone, shell, exoskeleton
• Tends to fossilize
• A large portion of individuals have no hard parts at all
o Marine + Lowland
• Buried in mud
• Especially burrowing marine organisms
• Found often in mud
o Recent
• Under-represented
o Soft parts
• Internal tissues
• 2/3 of extant taxa have no hard parts
• Single-celled organisms leave no fossils
o High elevation
o Old - more likely to be destroyed
Measuring extinction rates can be hard to standardize
• It can be based on the percentage of genera going extinct
o It refers to all species - we don't have enough data to determine individual species
• It can also be based on the percentage of families that go extinct
o Families of all taxa
• A lot of standardization goes into creating these charts - e do’t eed to ko aout data, just
know that it's either measured in terms of all species, or families of all taxa - just not individual
species
Permian Extinction
• Over half of all taxa went extinct over a period of 60 000 years
o Geographically, 60 000 years is a very short period of time
• A very rapid change in carbon isotopes at extinction (atmospheric change)
• Stratigraphy suggests a drop of oxygen in the ocean
• Flood Basalt Volcanism
o Not the "stereotypical" single volcano
o It was a long term release of basalt from large fissures
find more resources at oneclass.com
find more resources at oneclass.com
Document Summary
Paleozoic: 540 mya - cambrian radiation (radiation of animal phyla, colonization of land begins soon after - insects, land plants, tetrapods. First mammal-like animals appeared: 251 mya - permian mass extinction, there was a major change in animal life between paleozoic and mesozoic. Mesozoic: dinosaurs don"t emerge until after the permian era, cretaceous era - diversity of dinosaurs at its maximum, warm climate allows land plants to diversify. Cenozoic (tertiary/paleogene/neogene: emergence of different lineages of mammals, after 65 mya (mass extinction of dinosaurs, end-cenozoic - cyclical ice age, world-wide. Extinction: the two extinction events are important (250 mya - end-permian mass extinction, 65 mya - Survivorship curves: background extinction, there are 3 survivor ship curves. If you watch an individual from birth to death, their survivorship curve will be 1 of the 3 curves: linear - probability of species becoming extinct is the same regardless of age. It is the standard rate of extinction, the normal extinction rate.
