What’s the News: The loss of large animals is wreaking havoc on Earth’s ecosystems, according to a scientific review published in Science on Friday, causing food chains to fall into disarray, clearing the way for invasive species, and even triggering the transmission of infectious diseases. The decline and disappearance of these large animals, due in large part to human factors such as hunting and habitat loss, has such strong and wide-ranging effects that the review’s authors say it may well be “humankind’s most pervasive influence on nature.”

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What’s the News: Researchers have uncovered the youngest known dinosaur bone, dating from shortly before an asteroid slammed into Mexico’s Yucatan peninsula around 65 million years ago. The find, published today in Biology Letters, has revived debate among paleontologists over what, exactly, killed the dinosaurs.

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What’s the News: A fungus that his been wiping out frog species all over the world is creeping into the last area patch of tropical mountains in the Americas escape its scourge, the Darien National Park in Panama, and scientists are scrambling to save what species they can.

Frogs have been taking a beating over the last three decades, due in large part to a ruthless killer called chytrid fungus. Identified in the late ’90s, the fungus is startlingly lethal, driving 50% of species into extinction and killing 80% of individuals within five months of appearing at one location in Panama. It spreads through water via spores, affecting even areas where humans have not penetrated. “It is the worst infectious disease ever recorded among vertebrates in terms of the number of species impacted, and its propensity to drive them to extinction,” wrote a team of scientists in a 2005 World Conservation Union report [pdf].

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It’s no secret that an alarming number of species around the world, especially vertebrates, are in trouble. But is the notion that the Earth is on the brink of a sixth major extinction event—the first since the dinosaur die-off—true, or alarmist? In Nature this week, a team of scientists sought to answer the question directly by counting as many species (and extinctions) as they could in the fossil record and the recent historical record. The result is gloomy news: There’s still a chance to avert much of the crisis, but if nothing changes, such a mass extinction event really could happen in the span of just a few centuries.

Mass extinctions include events in which 75 percent of the species on Earth disappear within a geologically short time period, usually on the order of a few hundred thousand to a couple million years. It’s happened only five times before in the past 540 million years of multicellular life on Earth. (The last great extinction occurred 65 million years ago, when the dinosaurs were wiped out.) At current rates of extinction, the study found, Earth will enter its sixth mass extinction within the next 300 to 2,000 years. [MSNBC]

That range of time the researchers give is so large because of the great diversity of life—it makes it hard to track exactly how many species are disappearing, and how quickly. (Indeed, DISCOVER has covered how biologists are discovering many new species these days just as those species face extinction). So Anthony Barnosky and his team made conservative estimates based on the available evidence. For instance, they pegged the rate of mammal extinction at 80 species out of a total of 5,000-plus in the last five centuries. That may not sound like much, but when you consider the speed at which things typically happen on a geologic scale, it is a faster rate of species loss than the previous five mass extinctions saw, scientists believe.

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The Permian extinction event was the biggest shake-up of life that Earth has ever seen: in the “Great Dying” that took place 250 million years ago, more than 90 percent of marine species were killed and about 70 percent of land animals vanished. The cause of this catastrophe has been debated for years, but new research suggests that volcanic eruptions triggered massive coal fires that pumped pollution into the air, eventually poisoning the planet.

The study, published in Nature Geoscience, is based on new findings from arctic rocks that date back to the Permian period, when all of the planet’s land masses formed a supercontinent called Pangaea. When the researchers analyzed the rocks, they found signs of a coal-based apocalypse.

Besides the usual miniscule clumps of organic matter, they also found tiny bubble-filled particles called cenospheres. These frothy little blobs form only when molten coal spews into the atmosphere, the researchers say…. [The cenospheres] must have been created when massive amounts of molten rock—more than 1 trillion metric tons—erupted through overlying coal deposits in Siberia to form lava deposits known as the Siberian Traps. [ScienceNOW]

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This fossil of an ancient winged reptile, bought from a farmer in China’s Liaoning province, tells a dramatic tale. About 160 million years ago, a female pterosaur fractured its wing and sank to the bottom of a muddy lake. Somehow, in the process of either dying or decomposing, she expelled a single egg, which has been preserved through the ages.

That’s the story that researchers told in a study published in the journal Science, anyway. And if the remarkably preserved fossil of the reptile Darwinopterus is female, they say, it sheds light on the sex differences and mating rituals of the extinct species. The preserved egg also seems to reveal new details of pterosaur reproduction.

Pterosaurs were the first vertebrates to take to the air, first appearing in the fossil record some 220 million years ago in the late Triassic period. Before their demise 65 million years ago the group evolved to include the largest flying animals ever to live – some had a wingspan of 10 metres. [New Scientist]

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The Internet has been burning up with an ice age storyline over the past few days: Researchers in Japan led by Akira Iritani announced their plan to clone  a woolly mammoth within four to six years, recreating a colossal beast not seen on Earth in thousands of years. But as enthusiastic as DISCOVER is for cloned mammoths (and believe us, we’re psyched), the project is still a long way from success.

First, the backstory.

Researchers from Kinki University’s Graduate School of Biology-Oriented Science and Technology began the study in 1997. On three occasions, the team obtained mammoth skin and muscle tissue excavated in good condition from the permafrost in Siberia. However, most nuclei in the cells were damaged by ice crystals and were unusable. The plan to clone a mammoth was abandoned. [Daily Yamiuri]

That initial effort was a DISCOVER cover story back in 1999. Now, though, the dream is back, thanks to newly developed methods to get around that icy problem.

The team, which has invited a Russian mammoth researcher and two US elephant experts to join the project, has established a technique to extract DNA from frozen cells, previously an obstacle to cloning attempts because of the damage cells sustained in the freezing process. Another Japanese researcher, Teruhiko Wakayama of the Riken Centre for Developmental Biology, succeeded in 2008 in cloning a mouse from the cells of another that had been kept in temperatures similar to frozen ground for 16 years. [AFP]

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About 540 million years ago, things were looking pretty rosy for complex life on Earth. Conditions were favorable, and the diversity of multicellular organisms took off during the so-called Cambrian Explosion. Trilobites frolicked. Brachiopods abounded. And then, things went south.

Between 490 million and 520 million years ago, a swift extinction event wiped out many of the Cambrian lifeforms. Geologists Benjamin Gill and Graham Shields-Zhou thinks they have found the trigger right in the midst of that era. According to their study in this week’s Nature, the ocean’s oxygen level plunged and the sulfur levels rose sharply 499 million years ago, killing off species that could not quickly adapt. That included some, but not all, of the trilobites that ruled the seas of the time.

Gill’s team decided to look at a specific subset of Cambrian extinctions that began 499 million years ago and lasted for 2 million to 4 million years. Other researchers had proposed that low oxygen levels — a condition known as anoxia — could be involved. But no one had marshaled enough evidence to prove that. [Science News]

The key to showing it in this case is in the chemical compositions of the samples the team collected, which hold clues to the ocean conditions of the time.

Gill and his colleagues took samples of 500-million-year-old rock from six locations around the world and measured the amounts of various isotopes of carbon and sulphur. Both were significantly different from the norm, suggesting that enormous amounts of carbon and sulphur were being buried. In modern oceans, this only occurs in low-oxygen waters like the Black Sea. [New Scientist]

The next question is, what drove down the oxygen levels so quickly? To that, Gill doesn’t have an answer. But such cyclical dramatic changes driving extinction is the rule, not the exception—there were several events during the latter Cambrian when many species were wiped out, and anoxia could have been at play in some of those, too.

Related Content:
DISCOVER: Just One Bite And Life Took Off
80beats: Ancient Rocks Show Oxygen Was Abundant Long Before Complex Life Arose
80beats: How “Snowball Earth” Could Have Triggered the Rise of Life
80beats: One of the Earth’s Earliest Animals Left Behind “Chemical Fossils”

Image: Wikimedia Commons

The continued onslaught by white nose syndrome against North America’s bats is one of the stories of the year—number 13, in fact, on DISCOVER’s Top 100 of 2010. But some help soon could be on the way in the form of Endangered Species Act protection. Earlier this month, a group of conservationists and scientists filed an emergency petition with the United States Fish and Wildlife Service to list the little brown bat under the act.

Emergency listing for a species does happen, but not very often, says Ann Froschauer, national white-nose syndrome communications leader for FWS. “Given the urgency of white-nose syndrome and recent information about predicted declines in little brown bat populations, the Service is committed to quickly reviewing scientific information, both published and provided by organizations such as these, in assessing the status of little brown bats and other bat species affected by WNS.” [Scientific American]

Listing the bats as endangered could force government action to protect them, including increased funding and the designation of critical habitat.

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The demise of the dinosaurs 65 million years ago opened the door of opportunity for mammals to take over the Earth—that much is clear. What’s coming into focus, thanks to a study out in Science, is just how fast mammals maxed out their size once the terrible lizards were out of the way.

“For the first 140 million years of our evolutionary history we really did nothing—we were really kind of boring,” Felisa Smith, an associate professor of biology at the University of New Mexico and coauthor of the new study. … But across all of the major continents, during the first 25 million years after the dinosaurs were wiped out, mammals underwent an explosive growth spurt. By 42 million years ago, however, the researchers found, the intense growth had leveled off. [Scientific American]

Smith’s team surveyed fossils from around the world, including 32 different mammalian orders. No matter where they looked, she says, they saw the same pattern. Mammals that survived the extinction event were small, mostly rodent-sized. Then all over the planet they exploded in size during that period of 20 to 25 million years.

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The buzzwords of the week in Moscow are tiger and conservation.

Sunday marked the opening of the worldwide tiger summit, which brought together high-level representatives from the 13 tiger-habitat countries, including Russia and China, to discuss the best plan to save the tigers. The meeting goes through Wednesday.

Only about 3,200 tigers remain in the wild, and without help experts say populations will start to go extinct in less than 20 years.

“Here’s a species that’s literally on the brink of extinction,” said Jim Leape, director general of conservation group WWF. “This is the first time that world leaders have come together to focus on saving a single species, and this is a unique opportunity to mobilise the political will that’s required in saving the tiger.” [BBC News]

The working plan includes provisions to decrease poaching and smuggling of the tigers and calls for more protected habitats. Researchers say that if tigers are left alone and provided with enough habitat and prey, the population could double in 12 years.

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We know things are bad for biodiversity. But just how bad across the board? The scientists at the International Union for Conservation of Nature, as they will from time to time, just updated their Red List—an accounting of how much trouble vertebrate species face. According to them, one in five around the world is threatened, and the numbers are worse for groups like sharks and amphibians.

The survey results, which are coming out in the journal Science, are based on research conducted in nearly 40 countries. The 174 scientists studied about 25,000 species to estimate the condition of the approximately 56,000 species on the Red List. From IUCN’s release:

“The ‘backbone’ of biodiversity is being eroded,”says the emminent American ecologist and writer Professor Edward O. Wilson, at Harvard University. “One small step up the Red List is one giant leap forward towards extinction. This is just a small window on the global losses currently taking place.”

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From Ed Yong:

The bones of dinosaurs have told countless tales about their origins and behaviour, but dinosaurs left behind more than just their skeletons. As they walked about, they made tracks, and some of these also fossilised over time. They too are very informative and a new set, made by some of the dinosaurs’ closest relatives, reveals how these ruling reptiles rose to power at a leisurely pace.

Dinosaurs evolved during the Triassic period from among a broader group called the dinosauromorphs. These include all dinosaurs as well as their closest relatives, species like Lagerpeton and Lagosuchus that only just miss out on membership in the dinosaur club. Fossils of these latter animals are extremely rare and only ten or so species are well documented. Their tracks, on the other hand, are more common.

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Indeed [their footprints] suggest that the dinosauromorphs evolved in a geological heartbeat after the greatest mass extinction of all time, a cataclysmic event “when life nearly died”.

For more about the footprints, and how they might push back the date of these dinosauromorphs back to 250 million years ago, check out the rest of the post at Not Exactly Rocket Science.

Related Content:
Not Exactly Rocket Science: Walking with dinosaur ancestors – footprints put dinosaur-like beasts at scene of life’s great comeback
80beats: How Tyrannosaurs Grew from Tiny “Jackals” to Ferocious Giants
80beats: Apparent Discovery of Dino Blood May Finally Prove the Tissue Preserves

Image: American Museum of Natural History

When it comes to explaining why the woolly mammoths died out, “death from above” could be down for the count.

Nearly 13,000 years ago, North American megafauna like the mammoths and giant sloths—and even human groups like the people of the Clovis culture—disappeared as the climate entered a cold snap. As DISCOVER has noted before, there’s been a controversial hypothesis bubbling up saying that a comet impact caused it all, but other scientists have been shooting holes in that idea of the last couple years. In a study in this week’s Proceedings of the National Academy of Sciences, a team led by Tyrone Daulton pooh-poohs what may be the last major evidence that supports the impact idea.

That evidence takes the shape of nano-diamonds in ancient sediment layers, a material said to form during impacts only.

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During the Pleistocene epoch animals thought big: It was the age of the megafauna, when creatures like the mammoth, an 8-foot-long beaver, and a hippopotamus-sized wombat walked the Earth. But these giants vanished one by one, and scientists have long wondered why.

Debate over what caused the megafauna to die out has raged for 150 years, since Darwin first spotted the remains of giant ground sloths in Chile. Possible causes have ranged from human influence to climate change in the past, even to a cataclysmic meteor strike. [BBC]

Now, a discovery on the South Pacific island nation of Vanuatu seems to have answered the question for at least one species. Researchers have turned up the bones of a giant land turtle in a dump used by the people who settled on the islands 3,000 years ago, and lead researcher Trevor Worthy says the evidence strongly suggests that the turtles were hunted into extinction.

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