Extinction history and rates

• The lecture discusses the discovery of extinction as a biological reality and its implications, reviews historical extinctions from the past 500 years, compares common factors, and estimates background extinction rates.

Geological Timeline

• The most recent parts of the Cenozoic Era include the Pleistocene (2.6 million years ago to 12,000 years ago) and the Holocene (12,000 years ago to present), often combined as the Quaternary period.
• The lecture transitions from discussing the Pleistocene to the Holocene.

What Happened 12,000 Years Ago?

• Human cultural and technological evolution outpaced biological evolution.
• The Agricultural Revolution led to the domestication of plants and animals.
• Compared to pre-agricultural societies, agricultural societies worked harder, had more inequality, less diverse diets, new health issues, transformed the environment more permanently, and had more children.

Discovery of Extinction

• Early scientists like Linnaeus, pre-evolutionary theory, didn't consider species could die out.
• Fossils were often misinterpreted as unknown living species or mythical creatures.
• Georges Cuvier (1769-1832) compared woolly mammoth fossils to modern elephants, concluding the former was a distinct, extinct species.
• Cuvier attributed extinctions to prehistoric floods, inspired by the biblical narrative and was also racist.

Dodo

• Dodos were discovered by Dutch sailors in 1598 and extinct by 1662 in Mauritius.
• Extinction likely due to deforestation and introduced species, not just hunting.
• Linnaeus described dodos in 1758 without knowing they were extinct.
• DNA evidence places dodos in the pigeon family, along with another extinct species from a nearby island.
• Both were "accidental" extinctions, barely noticed at the time.

Great Auk

• The Great Auk (Pinguinus impennis) was a large, flightless bird of the North Atlantic.
• True penguins are named for their resemblance to the Great Auk but are found in the Southern Hemisphere.
• Great Auks were hunted for feathers, meat, and oil, often with extreme cruelty.
• The species went extinct in 1844 (possibly 1852).
• The last known individual was killed by someone intending to collect a specimen.

Passenger Pigeon

• Passenger pigeons once numbered in the billions in North America.
• A flock in 1866, was a mile wide, 300 miles long, and took 14 hours to pass, estimated at over 3.5 billion birds.
• Passenger pigeons had a short breeding season and nested in huge colonies.
• Destruction of forests for farmland and eradication as agricultural pests led to extinction.
• Martha, the last passenger pigeon, died in captivity in 1914.
• The extinction of the passenger pigeon demonstrates that even the most common species can go extinct.

Rocky Mountain Locust

• The extinction of passenger pigeons may have indirectly led to the spread of Lyme disease.
• A massive swarm in 1875 covered an area the size of California and included over 12 trillion individuals.
• Like the passenger pigeon, the rocky mountain locust was migratory with restricted breeding grounds.
• It was actively targeted as an agricultural pest and went extinct by 1902.
• Much of the knowledge about this species comes from frozen specimens.
• The rocky mountain locust was a major food source for many species.
• The extinction of the rocky mountain locust may be related to the decline of the Eskimo Curlew.

Thylacine (Tasmanian Wolf)

• The thylacine was a large marsupial carnivore from Australia.
• Government paid bounty hunters to kill them to protect livestock.
• It went extinct in the wild in 1930; the last one died in 1936.

Steller’s Sea Cow

• Steller’s Sea Cow grew up to 10 meters long and weighed 11 tons.
• It experienced a severe population decline due to climate change in the Paleolithic, but survived near Russian islands.
• It went extinct in 1768, and may be the first species knowingly described after extinction in 1780.

Common Factors in Extinctions

• Most historical extinctions involved humans killing the animals as the main factor.
• Current drivers of biodiversity decline are more indirect.

Extinction Math

• 20% of sirenians are extinct (Steller’s sea cow).
• 25% of mammal groups have gone extinct in the last 500 years.
• Most extinct mammals were from mainland.