A. Extinctions 1. Constant, background extinction rate - some very huge extinction events a. Raup Histogram - reviewed extinctions over million year intervals b. Found a couple of really huge extinctions - 96% of life on earth 2. Look at individual taxa - give a survivorship curve for taxa a. Diagonal line on a semi-log plot. B. Slick idea - there is a constant loss rate of species 1. Over most time spans. c. Marine taxa with planktonic larvae last longer than ones where young developed directly from egg 1. The more widespread you are, the more likely you are to survive. 2. Theory - species with small geographic ranges are easily killed off - those with large ranges are not easily killed off by small environmental changes 3. The Big Five Extinction events a. Mass extinctions are global in extent - involve lots of taxa and are rapid b. Five (six) extinctions; 1. Terminal Ordovician (440 Ma) 2. Late Devonian (365 Ma) 3. Permo-Triassic (250 Ma) 4. End Triassic (215 Ma) 5. Cretaceous-Tertiary (K-T) (65 Ma) 6. ?? Late Holocene (the present) c. Paleontologists use the extinctions to indicate the ends of eras B. Dating extinctions 1. Are they instantaneous? Could be 2. But, how would you know? 3. The last individual might not be captured by the fossil record 4. Need common fossil that can be sampled at close intervals a. K-T extinction proven to be very fast using bivalves and ammonites b. Can't say much from dinosaurs 5. Rarefaction technique - Answer question "How many species died/" A. If a random percentage of species living today were wiped out, how many genera, familes and orders would be wiped out entirely? B. Rarefaction curves - can calculate the species level impact of big five extinctions C. Permo-Triassic extinctions - the Mother of all extinctions 1. How bad was it a. 50 % of all families - 90 to 96 % of all species b. Only extinction in insects - 8 of 27 orders gone c. 21 of 27 reptile families d. 70% of marine invertebrates 2. How selective a. Narrow geographic range were doomed A. 35% of broadly distributed genera went extinct b. 93% of genera restricted tothe margins of particular ocean basins went extinct 3. What was the cause? A. Pangea - one enormous continent 1. This did not cause extinction - the continent existed before and after the extinction 2. Previous glacial age b. Siberian traps - flood basalts - enormous out pouring of basalt lava onto surface of earth 1. Largest outpouring of magma ever 2. Adds lots of head, carbon dioxide and sulfur dioxide to the atmosphere a. Connection with extinction is tenuous c. Big changes in ocean and atmosphere 1. Lowered sea level at Permo-Triassic border a. 40 % of continents covered by sea in Permian b. 10% in Triassic 2. C-13/C-12 ratio changes at boudary a. Release of carbon stored in organic matter and methane b. Could be drop in primary production of sea 3. Changes in Ocean chemistry a. Pyritic cherts laid down by late Permian ocean 1. Really weird - There should only be sulfide if the deep ocean is anoxic 2. Modern deep ocean is not anoxic B. Hypothesis that Pangea disrupted circulation of sea water 1. Stop new water from reaching the deep sea 2. High carbon dioxide in the deep sea c. Proposal that this anoxic soup suddenly circulated 1. Due to glacial meltwater? d. Glacial age 1. Cause? Sulfur dioxide from the Siberian flood basalts? d. Nobody really knows the cause of the late-Permian extinction\ D. Cretaceous-Tertiary extinction 1. Death of the dinosaurs. a. Always a problem - lots of ideas - most are wrong b. Real cause is impact of meteor - neat story 2. Impact hypothesis a. Luis Alvarez - found evidence for impact event 3. Evidence for Impact a. Iridium anomaly 1. Alvarez found that when you do an analysis of K-T boundary marine clays you find a spike in the element iridium a. Gubbio, Italy 2. Iridium is rare in the earth's crust, but common in meteors 3. Hypothesis that iridium is from impact of meteor a. How big? 1. Estimate amount of iridium 2. Figure out that impact was 10 km wide rock 4. Also found shocked quartz at K-T boundary - normally found only in meteor impact sites 5. Microtektites - tiny pieces of melted rock - tear-drop shaped - solidified in flight 6. 65 million year old crater in Mexico - Chicxulub crater under the Yucatan peninsula 4. How did it Kill? a. Lots of dust in atmosphere b. Lots of carbon dioxide and sulfur dioxide - acid rain c. Darkened skies for many years - no solar radiation d. Earthquakes - Deccan traps - Basalt flow just like Siberian Traps e. Enormous tidal wave - seen in Texas and Mexico f. Chemistry of ocean would have changed a lot. - no photosynthesis g. Wildfires 5. Is there a pattern to survival a. Extinctions not even across taxa b. Amphibians, crocodiles, mammals and turtles little effected c. Dinosaurs gone d. Only on order of bird survives e. Marine plankton decimated f. 35% of land plants go extinct - pollen shows a "fern spike" G. Extinctions not size-dependent 1. Extinction seems to be concentrated in North America 2. Species with wide geographic ranges survived (mollusks) a. Wide geographic ranges buffer against extinction E. Holocene extinction - The Human Meteor? 1. Quaternary - most recent geological epoch a. Characterized by advances and retreats of glaciers - like late Permian b. Last 2 milllion years c. Advances and retreats of glaciers occurred 20 times during Quaternary 1. Time since last retreat (10,000 years) called the Holocene 2. Quaternary fauna had lots of large mammals and birds a. Mastodon and Mammoth b. Ground Sloth c. Cave Bear d. Larger version of Buffalo e. hyenas, cheetahs, horses, large cats in North America - gone when Europeans arrived f. Condor had broader range than now g. 150 ( 300lb) beaver 3. Extinction a. 38 of 54 large bodied species died in North America (70%) b. 80% loss in South America c. 86% of large marsupials died in Australia d. Less severe impact in Europe and Asia e. Almost none in Africa - 4.5% loss - African forms essentially unchanged 4. Highly selective extinction a. large-bodied forms and not on all continents b. Timing different in different places a. 40,000 BP in Australia b. 10,000 BP in North America c. 2,000 BP in New Zealand 1. In New Zealand lost birds - Moas 5. Cause a. Climate change 1. Quaternary is a period of major climate change - should cause extinctions 2. But, why not earlier? - 20 glacial/interglacial cycles what is with this latest one? b. Human activities - Pleistocene overkill hypothesis 1. Timing of extinctions in each place are about when humans arrived a. North American extinctions at time of paleoindian arrival b. Clovis culture - Big game hunters (known from Archeology) 1. Special "fluted" points - very complex flint knapping 2. Clovis points found in large Quaternary mammal remains 2. Loss of large animals which reproduce the slowest a. Modern version of buffalo smaller than Pleistocene one b. Relationship between reproduction rate and size. 1. Big ones reproduce slowly c. Deer left 3. Why did this not happen in Africa? a. Humans evolved with African fauna 1. Humans evolved in Africa and colonized the world from there b. NorthAmerican mammals were naive towards human hunters c. African mammals were not. d. Scenario has been repeated on islands in recent times 6. Loss of the Polynesian Avifauna in the last 2,000 years a. Steadman and James studied the fossil birds of the Pacific islands 1. Well preserved - many islands are volcanic - leave lava pipes a. Lots of dead stuff in pipes - including bird fossils b. Also archeological digs 2. Found huge losses in last 2,000 years - 2,000 species lost a. 20% of all birds on earth! b. Hawaii lost 60 species when Polynesians arrived 1,500 BP c. New Zealand lost 44 bird species d. An island in Tonga has only 6 bird species left from 27 before colonization. 3. How and Why? a. Direct predation by humans - Moas are a good example b. Dogs, pigs and rats were brought ashore by Polynesian settlers 1. Most birds were probably ground-nesters a. Result is nest disturbance by introduced pests c. Probably caused by humans 1. This destruction did not happen in Galapagoes 2. They were only colonized in historical times 7. Are we in a time of mass extinction? 1. Up to now the losses do not match the Big 5 extinction events 2. Modern habitat destruction is a problem. - may accelerate extinctions F. Evolutionary Implications of Extinctions 1. History of earth puntuated by large extinctions a. Reset the clock of life on earth - allow new radiations 1. Not good or bad - They are just how it is b. Earth rotates around the sun in a shooting gallery with a crazy, blind marksman 2. What did the earth look like after the Big 5? a. Low diversity ecosystems 1. Abundance of stromatolites - constructions by blue-green algae a. Only found now in extreme environments 2. The "fern spike" at the earlies Tertiary a. Increase in abundance of ecological opportunits b. Ecosystems radically simplified after extinctions 1. Brachiopods in Denmark a. Gone for 3 million years after K-T extinction b. New taxa and a few old appear in 3 million years 1. "Lazarus" taxa - probably survived in refuges c. After mass extinctions ecosystems are massively altered 1. At Permo-Triassic border shallow water marine environments shift from brachiopods and bryozoa to mollusks - they remain that way today 2. At Permo-Triassic border lots of reptiles were wiped out to be replaced by dinosaurs turtles, crocodiles, mammals and pterosaurs a. Taxa survive through Mesozoic 3. At K-T border dinosaurs are gone and are replaced by mammals and birds a. Mammals and birds radiate into the groups we know today d. Rapid radiations follow extinctions 1. Radiations occur in ecological vacuum a. The mammals didn't outcompete the dinosaurs b. The dinosaurs were killed off by the meteor strikc and the mammals took over e. Lots of chance here 1. Big five defined the history of life 2. They are random events 3. Chance plays a large role in the processes responsible for adaptation & diversity f. How does this fit with Darwinian natural selection? 1. Old view that adaptation makes organisms fit the environment better and better a. If there is a turnover in taxa it is because the successor taxa are better adapted 2. Modern view is that survival of taxa may have a lot to do with chance a. Adaptive radiations may be very fast and be triggered by chance events