Vertebrate Extinction Events

• Learning objectives include recognizing trends in body size and functional diversity of large vertebrates since the Cretaceous extinction, explaining evidence informing the investigation into the Pleistocene megafaunal extinction, and contrasting the main competing hypotheses (human-caused vs. climate-caused).

Extinction Through Time

• The last mass extinction occurred at the end of the Cretaceous period, 65 million years ago.
• A more recent extinction event affected only large land vertebrates.
• The "big 5" mass extinctions all occurred in the Paleozoic and Mesozoic Eras.
• The Cenozoic Era began after the K-T (or K-Pg) mass extinction (65 Ma – present).
• The Pleistocene (2.6 mya – 12,000 ya) and the Holocene (12,000 ya – present) are the most recent parts of the Cenozoic, often lumped together as the Quaternary period.
• The Cretaceous Extinction killed nearly all large vertebrates.
• After the Cretaceous Extinction organisms diversified and began filling similar niches.
• The largest land mammal ever was Paraceratherium (34 Mya - 23Mya), a relative of rhinos that was as tall as a giraffe.
• Giant carnivores like Arctodus and Smilodon existed around 2.5 mya – 10,000 ya.
• Phorusrhachidae were giant birds that existed ~40 mya – 100,000 ya.
• Diprotodon was a giant marsupial that existed ~1.5 mya – 40,000 ya.
• Megalania was a giant lizard that existed ~1.5 mya – 50,000 ya.

Pleistocene Extinctions

• In the Americas, all mammals >1000 kg (and most >100 kg) went extinct during the Pleistocene.
• The extinction event was much less severe in Africa.
• The Quaternary/Pleistocene extinction event may be linked to humans or climate.
• Increased technological sophistication plays a role in understanding this event.
• The two main hypotheses for the Pleistocene megafauna extinctions are human cause and climate change.
• Studying ancient climates from ice core samples is a technological advancement that can go back ~100,000 years in the Arctic and nearly 1,000,000 in parts of Antarctica.
• Relevant climate events include the Last Glacial Maximum (LGM) from 31,000 to 16,000 years ago, the Bølling-Allerød interstadial (a warm moist period) from 14,690 to 12,890 years ago, and the Younger Dryas (a cold period) from 12,900 to 11,700 years ago (start of the Holocene).
• During the Last Glacial Maximum (~20,000 ya), the Earth was ~6°C colder than present, and sea level was ~100 m lower.
• The exact causes for the LGM are not entirely clear, but are probably related to long-term cycles in Earth’s orbital dynamics and potentially shifts in ocean currents.
• The Younger Dryas is named after abundant fossils of the arctic flower Dryas octopetalum.