Transcript Dec7_09
Extinction • Loss of a species or group of taxa • Primary cause: Failure of species to adapt to changes in environment • Extinction happens Example: Species Lifespan • Mammals ~ 1 million year lifespan • 5000 currently alive • Background rate ~ 1 species / 200 years • 89 species extinct in last 400 years www.pbs.org/wgbh/evolution/library/03/2/l_032_04.html Extinction Mass extinctions account for 4% of all extinctions The big 5 of the phanerozoic. Ordovician/Silurian Extinction • 490 – 443 mya • Diversification of phyla, including 21 classes of echinoderms • Formation of coral reefs • Evolution of agnathans and trilobites • Plants invade land • Gondwana centered in southern hemisphere Ordovician/Silurian Extinction • 57% of marine genera wiped out • Probable cause: Global cooling – Glaciation over Gondwana led to cooling and drop in sea levels • Time span: 2 my (rapid) • Created opportunity for surviving species: ostracoderms Permian/Triassic Extinction • Largest of mass extinctions • Lost 96% of marine species – Trilobites gone • Lost 75% of all land vertebrate families • Estimated that 84% of all genera on Earth became extinct • Time span: 1 million years • Prelude to the age of dinosaurs Permian/Triassic Extinction • Plate Tectonics – Pangea formation • Supernova – destroyed ozone layer • Asteroid impact – trigger volcanoes – Siberian traps – 200,000 cubic kilometers covered with lava – Global warming caused methane hydrate release from oceans – Oxygen depleted from oceans Cretaceous/Tertiary Extinction • Extinction of Dinosaurs – 50% of all genera – Pterosaurs, dinosaurs, sea reptiles • Cause: Asteroid impact • Prelude to the age of mammals Iridium concentration in clay layer at KT Boundary Other evidence: • Chicxulub crater • Microtektites • Soot deposits • Evidence of tsunami Normal Quartz Shocked Quartz Evidence of the Impact Abundant shocked quartz and microtektites in the KT clay layer in Caribbean Microtektites from the crater wall date to 65 mya Direct Effects: Tsunami, dust induced global cooling, fires, acid rain, earthquakes, volcanism Indirect Effects: Disruption of ecological processes and biogeochemical nutrient cycles. Broadly distributed species are more likely to survive extinction events Bivalve Genera Number of Geographical Provinces Jablonski and Raup, 1995 Habitat Destruction Current extinctions are occurring at 100 - 1000 times the normal or background rate. May et al. 1995, Pimm et al., 1995 Human Population by 2050 = 13 billion Vertebrates Cartilagenous Bony Hagfish, Fish Fish Amphibians Lampreys Reptiles Birds Mammals Hair Mammary Glands Amniotic Egg Endothermy Four Limbs Terrestrial Phase Bony Skeleton Swim Bladder Skull Backbone Paired Fins Jaws Mammals • Hair, mammary glands • Most advanced nervous system • Learning important to survival • Warm blooded • Humans are mammals Humans are primate mammals • Class Mammalia – Order Primates • Prosimians (e.g. lemurs) • Tarsiers • Anthropoids (e.g. monkeys, hominoids) Lemur Tarsier Macaque Primates : Humble Beginning Rabbit Primates Shrew Shrew-like Ancestor Major Primate Groups Family Hominidae Tarsiiformes Lemurs Old World Monkeys New World Monkeys Gibbons Orangutan Chimp Human Gorilla Homininae : African Great Apes and Humans Hominidea : Great Apes and Humans Hominoidea : Apes and Humans What Features Are Associated With Primate Evolution? I. Sensory Adaptations – Protected, forward looking eyes with stereoscopic vision – Improved sight : more detail even in low light – Reduction of olfactory structures What Features Are Associated With Primate Evolution? II. Adaptations for tree-climbing and insectivory – – – – Freely moving limbs and digits Long mobile digits capable of grasping Retention of tail as organ of balance Evolution of upright body posture and extensive head rotation – Increased body size – Evolution of nervous system to give precise and rapid control of movement