AP Biology – Lecture #4 Big Idea #1 – Life continues to evolve within a changing environment Adapted from Rebecca Rehder Wingerden ©

Speciation and extinction have occurred throughout the Earth’s History. Speciation rates can vary, especially when adaptive radiation occurs when new habitats become available. Monotremes (5 species) Ancestral mammal Ancestral Cynodont Marsupials (324 species) Eutherians (5,010 species) 250 200 150 100 50 0 MYA Adaptive radiation of mammals: Fossil evidence indicates that mammals underwent a dramatic adaptive radiation after the extinction of terrestrial dinosaurs 65.5 mya. Although mammals originated about 180 mya, the mammal fossils older than 65.5 mya are mostly small and not morphologically diverse.

Speciation and extinction have occurred throughout the Earth’s History. b. Species extinction rates are rapid at times of ecological stress. • Five major extinctions (mass extinctions)

Speciation and extinction have occurred throughout the Earth’s History. Ordovician-Silurian mass extinction (443 mya): Third largest extinction, 85% of sea life was wiped out. An ice age has been blamed for the extinctions - a huge ice sheet in the southern hemisphere caused climate change and a fall in sea level, and messed with the chemistry of the oceans. Late Devonian mass extinction (359 mya) Three quarters of all species on Earth died out. Life in the shallow seas were most affected. Changes in sea level, asteroid impacts, climate change and new kinds of plants messing with the soil have all been blamed for these extinctions.

Speciation and extinction have occurred throughout the Earth’s History. Permian mass extinction (248 mya) Nicknamed The Great Dying, 98% of species died out. Proposed causes; asteroid impact, flood basalt eruptions, catastrophic methane release, a drop in oxygen levels, sea level fluctuation or some combination of these. Marine creature were affected and insects suffered. Triassic-Jurassic mass extinction (200 mya) Roughly half of all the species became extinct. Climate change, flood basalt, eruptions and an asteroid impact have all been blamed for this loss life. Many types of animals died out, including marine reptiles, some large amphibians, and large numbers of cephalopod mollusks. Strangely, plants were not so badly affected.

Speciation and extinction have occurred throughout the Earth’s History. Cretaceous-Tertiary mass extinction (65 mya) Also known as the K/T extinction - is famed for the death of the dinosaurs. It’s suggested that the decline was due to flood basalt eruptions affecting the world’s climate, combined with drastic falls in sea level. There is also evidence of a huge asteroid or comet hitting the seabed near the Yucatan Peninsula in Mexico.

Speciation and extinction have occurred throughout the Earth’s History. Human impact on ecosystems and species extinction rates: Is a sixth mass extinction underway?

Speciation and extinction have occurred throughout the Earth’s History. Bozeman Biology: Speciation and Extinction (13:00 min.) http://www.bozemanscience.com/007- speciation-and-extinction Nova: Last Extinction Megabeasts’ Sudden Death (53:00 min.)