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  • richardmitnick 1:57 pm on April 20, 2015 Permalink | Reply
    Tags: , , Extinctions   

    From AAAS: “Sixth extinction, rivaling that of the dinosaurs, should join the big five, scientists say” 



    16 April 2015
    Eric Hand

    Clamlike brachiopods in a rock formation in Spitsbergen, Norway, went extinct in an event about 260 million years ago. Paul Wignall/University of Leeds

    Earth has seen its share of catastrophes, the worst being the “big five” mass extinctions scientists traditionally talk about. Now, paleontologists are arguing that a sixth extinction, 260 million years ago, at the end of a geological age called the Capitanian, deserves to be a member of the exclusive club. In a new study, they offer evidence for a massive die-off in shallow, cool waters in what is now Norway. That finding, combined with previous evidence of extinctions in tropical waters, means that the Capitanian was a global catastrophe.

    “It’s the first time we can say this is a true global extinction,” says David Bond, a paleontologist at the University of Hull in the United Kingdom. Bond led a study that was published online this week in the Geological Society of America Bulletin. He adds that in magnitude, the Capitanian event was on par with the dinosaur-killing extinction 66 million year ago. “I’d put this up there with it, albeit with slightly less attractive victims,” Bond says.

    Interest in the Capitanian began in the early 1990s, when paleontologists found evidence for fossil extinctions in rock formations in China. The rocks had originally formed on the floor of a shallow tropical sea. Most foraminifera—tiny, shelled protozoans—were wiped out, along with many species of clamlike brachiopods. There was also a possible trigger to blame: a set of ancient volcanic outbursts in China that solidified into rocks called the Emeishan Traps. The hot flood basalts would have released huge amounts of sulfur and carbon dioxide, potentially causing a quick global chill followed by a longer period of global warming. The gases could have also driven acidification and oxygen depletion in the oceans. Many scientists think that a similar massive burst of volcanic activity in Siberia touched off the biggest extinction of all time, just 8 million years later, at the end of the Permian period.

    But the older, less studied Capitanian extinction has been dogged by criticism that it may have been a regional event, or just part of a gradual trend en route to the larger Permian extinction. Some of those criticisms may be quelled by the new evidence, which comes from Spitsbergen, the largest island in the Svalbard archipelago off the coast of Norway in the Arctic Ocean. There, Bond and his colleagues examined chert rocks—silica formations, created by the skeletons of dead sponges, that also contain many species of brachiopods. At the time, the rocks would have been forming in tens of meters of cooler water at midlatitudes. But at a stark point in the rock record, the fossils disappeared.

    “They all drop out,” says study co-author Paul Wignall, a paleontologist at the University of Leeds in the United Kingdom. “It’s like a blackout zone and there’s nothing around.” A little further in the rock record, a few brachiopod species recover, Wignall says, and then mollusks take over en masse, before the devastation of the Permian extinction, 8 million years later.

    The research team had a hard time tying the new record to the same moment in fossil records in China. Isotopic dating systems are too uncertain to provide a helpful absolute date. Another standard biostratigraphic method—linking the timing of different rock layers by the comings and goings of fossilized teeth of tiny eellike creatures called conodonts—also couldn’t be used, because the same species didn’t live in cool and tropical waters. Instead, the team points out that similar swings in different isotopes’ levels, occurring in both parts of the world, suggest that the two regions were experiencing the same changes in ocean chemistry at the same time.

    That’s part of the problem, says Matthew Clapham, a paleontologist at the University of California, Santa Cruz. He thinks the study team has dated something a bit younger—maybe 255 million years old. “They’ve definitely identified a real event, which is really interesting,” he says. “Their age model is less convincing.” He also says that recent work in China on the extent of the Capitanian extinction across different species shows it may not have been quite as bad as originally thought. Clapham thinks the Capitanian is probably 30th or 40th in the hierarchy of extinctions, not sixth.

    But Bond is still convinced that the Capitanian will go down in the history books as one of the world’s worst. “You have to change a lot of people’s minds,” he says. He is now studying fossil records in Russia and Greenland that could further buttress his arguments for a global disaster. Clapham, too, wants to see more work done on this enigmatic stretch of Earth history. “It’s a very mysterious event—it’s an interesting thing to study,” he says.

    See the full article here.

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  • richardmitnick 6:30 am on February 10, 2015 Permalink | Reply
    Tags: , , , Extinctions   

    From BBC: “Mammals on brink of ‘extinction calamity'” in Australia 


    10 February 2015
    Helen Briggs

    The endangered northern quoll, a mammal species native to Australia

    Australia has lost one in ten of its native mammals over the last 200 years in what conservationists describe as an “extinction calamity”.

    No other nation has had such a high rate of loss of land mammals over this time period, according to scientists at Charles Darwin University, Australia.

    The decline is mainly due to predation by the feral cat and the red fox, which were introduced from Europe, they say.

    Large scale fires to manage land are also having an impact.

    As an affluent nation with a small population, Australia’s wildlife should be relatively secure from threats such as habitat loss.

    But a new survey of Australia’s native mammals, published in the journal Proceedings of the National Academy of Sciences, suggests the scale of the problem is more serious than anticipated.

    Since 1788, 11% of 273 native mammals living on land have died out, 21% are threatened and 15% are near threatened, the study found. Marine mammals are faring better.

    Shy species

    “No other country has had such a high rate and number of mammal extinctions over this period, and the number we report for Australia is substantially higher than previous estimates,” said conservation biologist John Woinarski, who led the research.

    “A further 56 Australian land mammals are now threatened, indicating that this extremely high rate of biodiversity loss is likely to continue unless substantial changes are made.

    “The extent of the problem has been largely unappreciated until recently because much of the loss involves small, nocturnal, shy species with [little] public profile – few Australians know of these species, let alone have seen them, so their loss has been largely unappreciated by the community.”

    The brush-tailed rabbit-rat, a mammal species native to Australia that is listed as a near-threatened species by the International Union for Conservation of Nature The brush-tailed rabbit-rat, a mammal species native to Australia that is listed as a near-threatened species by the International Union for Conservation of Nature

    In time, iconic species such as the koala will also decline, said the researchers, from Charles Darwin University, Southern Cross University and the Department of Parks and Wildlife in Wanneroo.

    The prospects for Australia’s wildlife can be improved but is “a very formidable challenge”, they added.

    It is estimated there are between 15 and 23 million wild cats living on the continent.

    Practical measures to protect native species include boosting biosecurity on islands off the mainland, which have fewer feral cats and foxes.

    The islands could also act as arks for endangered species, while more careful use of fire and control measures to wipe out foxes and feral cats are also being considered.

    But the researchers warn that Australians may ultimately need to consider the way they live on the land to stem the loss of natural assets.

    See the full article here.

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  • richardmitnick 6:43 am on December 21, 2014 Permalink | Reply
    Tags: , , Extinctions   

    From astrobio.net: “Asteroid that wiped out dinosaurs may have nearly knocked off mammals, too” 

    Astrobiology Magazine

    Astrobiology Magazine

    Dec 20, 2014
    Source: Pensoft Publishers

    The extinction of the dinosaurs 66 million years ago is thought to have paved the way for mammals to dominate, but a new study shows that many mammals died off alongside the dinosaurs.

    Metatherian mammals–the extinct relatives of living marsupials (“mammals with pouches”, such as opossums) thrived in the shadow of the dinosaurs during the Cretaceous period. The new study, by an international team of experts on mammal evolution and mass extinctions, shows that these once-abundant mammals nearly followed the dinosaurs into oblivion.

    Part of skeleton of Lycopsis longirostris, a fossil marsupial
    Lycopsis is an extinct genus of South American metatherian, that lived during the Miocene.

    When a 10-km-wide asteroid struck what is now Mexico at the end of the Cretaceous and unleashed a global cataclysm of environmental destruction, some two-thirds of all metatherians living in North America perished. This includes more than 90% of species living in the northern Great Plains of the USA, the best area in the world for preserving latest Cretaceous mammal fossils.

    This diagram is showing how severely metatherian mammals were affected when an asteroid hit Earth at the end of the Cretaceous, 66 million years ago. In North America, the number of metatherian species dropped from twenty species within the last million years of the Cretaceous Period, to just three species in the first million years of the Paleogene Period. Credit: Dr Thomas Williamson

    In the aftermath of the mass extinction, metatherians would never recover their previous diversity, which is why marsupial mammals are rare today and largely restricted to unusual environments in Australia and South America.

    Taking advantage of the metatherian demise were the placental mammals: species that give live birth to well-developed young. They are ubiquitous across the globe today and include everything from mice to men.

    Dr. Thomas Williamson of the New Mexico Museum of Natural History and Science, lead author on the study, said: “This is a new twist on a classic story. It wasn’t only that dinosaurs died out, providing an opportunity for mammals to reign, but that many types of mammals, such as most metatherians, died out too – this allowed advanced placental mammals to rise to dominance.”

    Dr. Steve Brusatte of the University of Edinburgh‘s School of GeoSciences, an author on the report, said: “The classic tale is that dinosaurs died out and mammals, which had been waiting in the wings for over 100 million years, then finally had their chance. But our study shows that many mammals came perilously close to extinction. If a few lucky species didn’t make it through, then mammals may have gone the way of the dinosaurs and we wouldn’t be here.”

    Dr. Gregory Wilson of the University of Washington also took part in the study.

    The new study is published in the open access journal ZooKeys. It reviews the Cretaceous evolutionary history of metatherians and provides the most up-to-date family tree for these mammals based on the latest fossil records, which allowed researchers to study extinction patterns in unprecedented detail.

    See the full article here.

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  • richardmitnick 2:25 pm on September 2, 2014 Permalink | Reply
    Tags: , , Extinctions   

    From Brown: “Extinctions during human era worse than thought” 

    Brown University
    Brown University

    September 2, 2014
    David Orenstein 401-863-1862

    It’s hard to comprehend how bad the current rate of species extinction around the world has become without knowing what it was before people came along. The newest estimate is that the pre-human rate was 10 times lower than scientists had thought, which means that the current level is 10 times worse.

    Extinctions are about 1,000 times more frequent now than in the 60 million years before people came along. The explanation from lead author Jurriaan de Vos, a Brown University postdoctoral researcher, senior author Stuart Pimm, a Duke University professor, and their team appears online in the journal Conservation Biology.

    “This reinforces the urgency to conserve what is left and to try to reduce our impacts,” said de Vos, who began the work while at the University of Zurich. “It was very, very different before humans entered the scene.”

    In absolute, albeit rough, terms the paper calculates a “normal background rate” of extinction of 0.1 extinctions per million species per year. That revises the figure of 1 extinction per million species per year that Pimm estimated in prior work in the 1990s. By contrast, the current extinction rate is more on the order of 100 extinctions per million species per year.

    Orders of magnitude, rather than precise numbers are about the best any method can do for a global extinction rate, de Vos said. “That’s just being honest about the uncertainty there is in these type of analyses.”

    Jurriaan de Vos
    “This reinforces the urgency to conserve what is left and to try to reduce our impacts. It was very, very different before humans entered the scene.” Photo: David Orenstein/Brown University

    From fossils to genetics

    The new estimate improves markedly on prior ones mostly because it goes beyond the fossil record. Fossils are helpful sources of information, but their shortcomings include disproportionate representation of hard-bodied sea animals and the problem that they often only allow identification of the animal or plant’s genus, but not its exact species.

    What the fossils do show clearly is that apart from a few cataclysms over geological periods — such as the one that eliminated the dinosaurs — biodiversity has slowly increased.

    The new study next examined evidence from the evolutionary family trees — phylogenies — of numerous plant and animal species. Phylogenies, constructed by studying DNA, trace how groups of species have changed over time, adding new genetic lineages and losing unsuccessful ones. They provide rich details of how species have diversified over time.

    “The diversification rate is the speciation rate minus the extinction rate,” said co-author Lucas Joppa, a scientist at Microsoft Research in Redmond, Wash. “The total number of species on earth has not been declining in recent geological history. It is either constant or increasing. Therefore, the average rate at which groups grew in their numbers of species must have been similar to or higher than the rate at which other groups lost species through extinction.”

    The work compiled scores of studies of molecular phylogenies on how fast species diversified.

    For a third approach, de Vos noted that the exponential climb of species diversity should take a steeper upward turn in the current era because the newest species haven’t gone extinct yet.

    “It’s rather like your bank account on the day you get paid,” he said. “It gets a burst of funds — akin to new species — that will quickly become extinct as you pay your bills.”

    By comparing that rise of the number of species from the as-yet unchecked speciation rate with the historical trend (it was “log-linear”) evident in the phylogenies, he could therefore create a predictive model of what the counteracting historical extinction rate must have been.

    The researchers honed their models by testing them with simulated data for which they knew an actual extinction rate. The final models yielded accurate results. They tested the models to see how they performed when certain key assumptions were wrong and on average the models remained correct (in the aggregate, if not always for every species group).

    All three data approaches together yielded a normal background extinction rate squarely in the order of 0.1 extinctions per million species per year.

    A human role

    There is little doubt among the scientists that humans are not merely witnesses to the current elevated extinction rate. This paper follows a recent one in Science , authored by Pimm, Joppa, and other colleagues, that tracks where species are threatened or confined to small ranges around the globe. In most cases, the main cause of extinctions is human population growth and per capita consumption, although the paper also notes how humans have been able to promote conservation.

    The new study, Pimm said, emphasizes that the current extinction rate is a more severe crisis than previously understood.

    “We’ve known for 20 years that current rates of species extinctions are exceptionally high,” said Pimm, president of the conservation nonprofit organization SavingSpecies. “This new study comes up with a better estimate of the normal background rate — how fast species would go extinct were it not for human actions. It’s lower than we thought, meaning that the current extinction crisis is much worse by comparison.”

    Other authors on the paper are John Gittleman and Patrick Stephens of the University of Georgia.

    See the full article here.

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