Category: Environment

{Neither a giant asteroid nor a gradual die out can take full blame for dinosaurs’ demise.}

Rather, the culprit may be both, two new studies suggest.

Tens of millions of years before the asteroid delivered its killer blow some 66 million years ago, the number of dinosaur species had already begun to drop, researchers report online April 18 in the Proceedings of the National Academy of Sciences. But not all dino groups were in decline, including some maniraptoran dinosaurs, a different group of researchers suggests online April 21 in Current Biology.

At first glance, the two studies seem to conflict, but “they can coexist,” says paleontologist Michael Benton, who coauthored the PNAS paper. Both studies add to what has become an increasingly intricate picture of dinosaurs’ final days.

“Things are a wee bit more complicated than we used to think,” says Benton, of the University of Bristol in England.

In the 1960s and ‘70s, scientists generally believed that dinosaurs petered out after a long, gradual decline. That view took a U-turn in 1980, when researchers proposed that, instead, an asteroid impact might have suddenly triggered the extinction. “The flip-flop was quite extreme,” Benton says of the changed thinking. “Dinosaurs went from long-term decline to instant death.”

What actually happened, he says, is probably more nuanced. Benton and colleagues analyzed the number of dinosaur species emerging and going extinct over a huge timescale: roughly 175 million years. Around 40 million to 50 million years before the mass extinction, dinosaurs started losing species faster than they were gaining new ones, the researchers found. This loss in diversity could have made it harder for dinosaurs to bounce back from the asteroid’s catastrophic impact.

“This doesn’t in any way attack the importance of the impact,” Benton says. But across the board, he says, dinosaur species numbers were dwindling. At least two groups, however, seemed to buck the trend. Hadrosaurs (duck-billed dinosaurs) and ceratopsids (the group that includes Triceratops) were booming up until the end, the team found.

According to the Current Biology analysis, toothed maniraptorans (small birdlike relatives of velociraptors) were thriving, too. A detailed examination of more than 3,000 of these dinosaurs’ teeth suggests that these dinos’ ecosystem was pretty stable millions of years before the extinction, says study coauthor Derek Larson, a paleontologist at the Philip J. Currie Dinosaur Museum in Alberta and the University of Toronto.

Larson and colleagues looked for variations in the teeth’s dimensions, and the size of tooth serrations. Then they determined how much that variation changed over time. Big changes could be a hint that these dinos were on the decline, Larson says. But instead, “things basically stayed the same through the last 18 million years of the Cretaceous,” he says.

Toothed maniraptorans “seemed to be doing just fine right up until the extinction,” says University of Oxford paleobiologist Roger Benson, who was not involved in either study.

Larson’s team wondered why the toothed, meat-eating maniraptorans went extinct after the impact while their relatives — the beaked ancestors of modern birds — didn’t. The answer could be dietary, the researchers propose. They analyzed the diets of modern birds to try and figure out what an ancestral bird might have eaten. It probably relied on seeds, Larson says, a hardy food source that could have lasted for decades.

Seeds might have sustained ancient birds through a “nuclear winter,” the debris-darkened skies that could have blotted out the sun following an asteroid impact. When hoards of plants and animal species died out, and dinosaurs ran out of food, he says, “the only resource that would have been reliable and available would have been seeds.”

{In rare instances, DNA is known to have jumped from one species to another. If a parasite’s DNA jumps to its host’s genome, it could leave evidence of that parasitic interaction that could be found millions of years later — a DNA ‘fossil’ of sorts. An international research team led from Uppsala University has discovered a new type of so-called transposable element that occurred in the genomes of certain birds and nematodes.}

The results are published in Nature Communications.

Dr. Alexander Suh at Uppsala University is an expert on the small stretches of DNA that tend to jump from one place to another, called transposable elements. Working with a team from eleven institutions in five countries, the researchers discovered a new type of transposable element that occurred in certain bird genomes but not others.

By searching DNA databases, the team discovered that the only other animals that shared the new transposable element were nematode worms that are parasites of humans and other mammals.

‘This finding was so unexpected that we were literally speechless at first,’ says Alexander Suh.

By comparing the DNA sequences of each instance of the transposable element, Suh and his team were able to figure out that the transfer of DNA between nematodes and birds occurred in two waves across the entire tropics, including remote places like Madagascar. They involved charismatic groups of birds such as parrots, hummingbirds, manakins.

Certain human diseases, such as avian flu and HIV/AIDS, are known to have jumped onto our species from animal hosts. Epidemiologists have only recently realized the importance of these so-called ‘zoonoses’. However, there are many more human diseases whose host-origins are unknown. These include lymphatic filariasis and loiasis, two serious human tropical diseases that are caused by nematode worms and spread by mosquitoes. The present study reveals that these modern human parasite species were parasites of birds from at least 25-17 million years ago. They probably did not infect mammals at the time that the transposable element was actively jumping between species, because there is no trace of it in mammal genomes.

The genomes show that the bird parasites were widespread because they infected different bird groups that occurred in each of the world’s major tropical regions and would have been isolated from each other at the time.

Genome sequences continue to reveal evolutionary history in surprising ways. Not only can comparisons of genomes assess relatedness, but interactions between specific host and parasite species can also be permanently recorded in the genome via jumping of transposable element DNA from one to the other. In this first example of that phenomenon in birds and nematodes, we learned that a class of parasites that is a present-day scourge once switched hosts from birds to mammals — a process that is all too familiar to modern epidemiologists.

{A new study in the April 22 edition of Science reveals that volcanic activity associated with the plate-tectonic movement of continents may be responsible for climatic shifts from hot to cold over tens and hundreds of millions of years throughout much of Earth’s history.}

The study, led by researchers at The University of Texas at Austin Jackson School of Geosciences, addresses why the Earth has fluctuated from periods when the planet was covered in ice to times when even the polar regions were ice-free.

The study explores very long-term shifts in Earth’s baseline climate, not short-term or human-induced climate change.

Lead researcher Ryan McKenzie said the team found that periods when volcanoes along continental arcs were more active coincided with warmer, or greenhouse, conditions over the past 720 million years. Conversely, periods when continental arc volcanos were less active coincided with colder, or icehouse, conditions.

Continental volcanic arc systems such as the Andes Mountains are created at active continental margins where two tectonic plates meet and the oceanic plate descends under the continental plate, forming a subduction zone. When this happens, magma mixes with carbon trapped in the Earth’s crust and releases carbon dioxide (CO2) gas into the atmosphere when volcanoes in the system erupt.

“Continental arc systems are plumbed through the Earth’s crust and they tend to interact with carbon reservoir rock preserved beneath the surface,” said McKenzie, who began the work as a postdoctoral researcher at the Jackson School and finished the study at Yale University.

Scientist have long known that the amount of carbon dioxide in the atmosphere influences the Earth’s climate, McKenzie said. The unanswered question is what caused the fluctuations in CO2 observed in the geologic record. Other theories have suggested that geological forces such as mountain building have, at different times in the planet’s history, introduced large amounts of new material to the Earth’s surface, and weathering of that material has drawn CO2 out of the atmosphere. The new study points to the amount of CO2 being released into the atmosphere, rather than the amount removed from it, as the primary driver of Earth’s climate.

Using nearly 200 published studies and their own fieldwork and data, researchers created a global database to reconstruct the volcanic history of continental margins over the past 720 million years.

“We studied sedimentary basins next to former volcanic arcs, which were eroded away over hundreds of millions of years,” said co-author Brian Horton, a professor in the Jackson School’s Department of Geological Sciences. “The distinguishing part of our study is that we looked at a very long geologic record — 720 million years — through multiple greenhouse-icehouse events.”

Specifically, researchers looked at the uranium-lead crystallization ages of the mineral zircon, which is largely created during continental volcanic arc activity. Zircon is less common in other types of volcanic settings, such as hot spots like Hawaii or island arc volcanoes such as the Marianas, so the mineral can be used to track continental arc volcanism. For the study, they looked at data for roughly 120,000 zircon grains from thousands of samples across the globe.

“We’re looking at changes in zircon production on various continents throughout Earth’s history and seeing how the changes correspond with the various icehouse and greenhouse transitions,” McKenzie said. “Ultimately, we find that during intervals of high zircon production we have greenhouse conditions, and as zircon production diminishes, we see a shift into our icehouse conditions.”

The cooler icehouse periods tended to correlate with the assembly of the Earth’s supercontinents, which was a time of diminished continental volcanism, Horton said. The warmer greenhouse periods correlated with continental breakup, a time of enhanced continental volcanism.

Jackson School researchers Shannon Loomis and Daniel Stockli, Yale University’s Noah Planavsky, and Rice University’s Cin-Ty Lee also worked on the study. The research was funded by the National Science Foundation.

{Seven fossil teeth exposed by the Panama Canal expansion project are the first evidence of a monkey on the North American continent before the Isthmus of Panama connected it to South America 3.5 million years ago. A team including Carlos Jaramillo, staff scientist at the Smithsonian Tropical Research Institute (STRI), published this discovery online in the journal, Nature today. They named the new monkey species Panamacebus transitus in honor of Panama and the monkey’s movement across the ancient seaway that divided North and South America.}

The 21 million-year-old teeth were found in the Las Cascadas Formation during a five-year intensive fossil salvage project by field crews from STRI, the University of Florida and the New Mexico Museum of Natural History and Science. Most of the mammal groups represented in the Las Cascadas formation have North American origins, despite the fact that South America is much closer, supporting the idea that Central America and western Panama represented a long peninsula extending south from North America.

During the salvage project, researchers rushed in behind engineers as they dynamited the steep canal banks. The researchers collected exposed fossils and described each location before heavy rains and fast-growing vegetation obscured evidence of the dramatic tectonic events that lifted the land bridge out of the sea to connect North and South America.

“I asked my boss for a million dollars to dig a hole in the ground,” said Jaramillo. “Then the Panamanian people voted for the Panama Canal Authority to spend $5.6 billion dollars to expand the Canal and unlocked a treasure trove for us, containing this new monkey species and many other fossils.”

“We suggest that Panamacebus was related to the capuchin (also known as “organ-grinder” monkeys) and squirrel monkeys that are found in Central and South America today,” said Jonathan Bloch, curator of vertebrate paleontology at the Florida Museum of Natural History on the University of Florida campus and lead author on the study. “Prior to this discovery, New World monkeys were thought to have evolved in isolation on South America, cut-off from North America by a wide seaway.”

Before the monkey teeth were discovered, the oldest evidence of movement of a mammal from South to North America are 8.5–9 million-year-old fossil remains of giant sloths. The authors of this report suggest two explanations: 1) that mammals from South America were more adapted to life in the South American derived forests still found in Panama and Costa Rica than to other forest types characteristic of Northern Central America or 2) that the lack of exposed fossil deposits throughout Central America means that evidence of these dispersals has yet to be revealed.

{Many scientists fear that global warming will hit staple food crops hard, with heat stress, extreme weather events and water shortages. On the other hand, higher levels of carbon dioxide–the main cause of ongoing warming–is known to boost many plants’ productivity, and reduce their use of water. So, if we keep pouring more CO2 into the air, will crops fail, or benefit? A new study tries to disentangle this complex question. It suggests that while greater warmth will reduce yields of some crops, higher CO2 could help mitigate the effects in some regions, unless other complications of global warming interfere.}

The study, by 16 researchers from a half-dozen countries, uses newly available crop models and data from ongoing large-scale field experiments. It appears this week in the journal Nature Climate Change.

“Most of the discussion around climate impacts focuses only on changes in temperature and precipitation,” said lead author Delphine Deryng, an environmental scientist at Columbia University’s Center for Climate Systems Research, the NASA Goddard Institute for Space Studies and the University of Chicago’s Computation Institute. “To adapt adequately, we need to understand all the factors involved.” Deryng cautions that the study should not be interpreted to mean that increasing carbon dioxide is a friend to humanity–only that its direct effects must be included in any calculation of what the future holds.

Many studies say that as temperatures rise, crops across the world will suffer as average temperatures become unsuitable for traditionally grown crops, and droughts, heat waves or extreme bouts of precipitation become more common. Agricultural scientists say that losses could be mitigated to some extent by switching crops, developing varieties adapted to the new conditions, or moving some crop-growing regions poleward. But such adaptations pose daunting challenges.

Due to human activities, average global levels of atmospheric carbon dioxide have risen by more than a quarter since 1960; they now stand at around 400 parts per million, and are expected to keep increasing, along with temperature. At the same time, experiments since the 1980s have shown that higher levels of carbon dioxide in the air helps plants build biomass. The concept is relatively simple; plants take in carbon to build their tissues, and if there is more carbon around, they have an easier time. Leaves take in air through tiny openings called stomata, but in the process the stomata lose water; with more carbon available, they don’t have to open up as much, and conserve moisture.

However, much of the initial evidence for so-called CO2 fertilization has come from lab experiments on isolated plants. These do not account for environmental factors that might affect plants even more powerfully in a warming world, including possibly increased insect and fungus attacks. Thus, suggestions that the greenhouse gas itself might prove a boon to crops have aroused deep skepticism.

In 2014, Deryng and her colleagues published the first global calculation of how heat waves might affect crops, and found that maize, spring wheat and soybeans would all suffer. When they added the effects of carbon-dioxide fertilization, they found that maize yields would still go down–but that spring wheat and soybeans might actually go up. Some media misinterpreted the study to say that climate change might help agriculture overall. The picture is much more complicated, say the authors.

The new study looks at how rising temperatures and carbon dioxide along with changes in rainfall and cloud cover might combine to affect how efficiently maize, soybeans, wheat, and rice can use water and grow. It confirms that heat and water stress alone will damage yields; but when carbon dioxide is accounted for, all four crops will use water more efficiently by 2080.

Based on the current biomass of these crops, water-use efficiency would rise an average of 27 percent in wheat; 18 percent in soybeans; 13 percent in maize; and 10 percent in rice. All things considered, the study projects that average yields of current rain-fed wheat areas (mostly located in higher latitudes including the United States, Canada and Europe), might go up by almost 10 percent, while consumption of water would go down a corresponding amount. On the other hand, average yields of irrigated wheat, which account for much of India and China’s production, could decline by 4 percent. Maize, according to the new projections, would still be a loser most everywhere, even with higher water efficiency; yields would go down about 8.5 percent. The study is less conclusive on the overall effects on rice and soybean yields; half of the projections show an increase in yield and half a net decline.

Deryng says the study is sturdier than past research, because it uses new data from experiments done in actual farm fields, and a half-dozen global crop models, several of which only recently became available. Nevertheless, she says, the uncertainties remain large. Field experiments, which involve blowing CO2 over sizable farm fields for entire growing seasons, have been done only at a handful of sites in the United States, Germany, Australia, Japan and China–not in Africa, India or Latin America, where subsistence farming are mainstays of daily life. She noted that greater yield also might not translate to more nutrition. For example, greater carbon uptake might not be balanced by other nutrients such as nitrogen, and trace elements like zinc and iron that are needed to make crops nutritious.

Bruce Kimball, a retired researcher with the U.S. Department of Agriculture who has studied crop-CO2 interactions, said the paper does “a good job on a huge scale,” though, he said, “more data from more crops from more locations” is needed.” Kimball cautioned also that previous research has shown that the benefits of higher CO2 levels tend to bottom out after a certain point — but that the damage done by heat only gets worse as temperatures mount. “Thus, for greater warming and higher CO2 the results would likely be more pessimistic than shown in this paper,” he said.

{Dinosaurs were already in an evolutionary decline tens of millions of years before the meteorite impact that finally finished them off, new research has found.}

The findings provide a revolution in the understanding of dinosaur evolution. Palaeontologists previously thought that dinosaurs were flourishing right up until they were wiped out by a massive meteorite impact 66 million years ago. By using a sophisticated statistical analysis in conjunction with information from the fossil record, researchers at the Universities of Reading, UK and Bristol, UK showed that dinosaur species were going extinct at a faster pace than new ones were emerging from 50 million years before the meteorite hit.

The analyses demonstrate that while the decline in species numbers over time was effectively ubiquitous among all dinosaur groups, their patterns of species loss were different. For instance, the long-necked giant sauropod dinosaurs were in the fastest decline, whereas theropods, the group of dinosaurs that include the iconic Tyrannosaurus rex, were in a more gradual decline.

Dr Manabu Sakamoto, University of Reading, the palaeontologist who led the research, said: “We were not expecting this result. While the asteroid impact is still the prime candidate for the dinosaurs’ final disappearance, it is clear that they were already past their prime in an evolutionary sense.”

{{‘Losing their edge’}}

“Our work is ground-breaking in that, once again, it will change our understanding of the fate of these mighty creatures. While a sudden apocalypse may have been the final nail in the coffin, something else had already been preventing dinosaurs from evolving new species as fast as old species were dying out.

“This suggests that for tens of millions of years before their ultimate demise, dinosaurs were beginning to lose their edge as the dominant species on Earth.”

Professor Mike Benton of the University of Bristol, one of the co-authors of the research, said: “All the evidence shows that the dinosaurs, which had already been around, dominating terrestrial ecosystems for 150 million years, somehow lost the ability to speciate fast enough. This was likely to have contributed to their inability to recover from the environmental crisis caused by the impact.”

It is thought that a giant asteroid’s impact with Earth 66 million years ago threw up millions of tonnes of dust, blacking out the sun, causing short-term global cooling and widespread loss of vegetation. This ecological disaster meant that large animals reliant on the abundance of plants died out, along with the predators that fed on them.

The new research suggests that other factors, such as the break-up of continental land masses, sustained volcanic activity and other ecological factors, may possibly have influenced the gradual decline of dinosaurs.

{{‘Room for mammals’}}

This observed decline in dinosaurs would have had implications for other groups of species. Dr Chris Venditti, an evolutionary biologist from the University of Reading and co-author of paper said: “The decline of the dinosaurs would have left plenty of room for mammals, the group of species which humans are a member of, to flourish before the impact, priming them to replace dinosaurs as the dominant animals on earth.”

Dr Sakamoto points out that the study might provide insight into future biodiversity loss. He said: “Our study strongly indicates that if a group of animals is experiencing a fast pace of extinction more so than they can replace, then they are prone to annihilation once a major catastrophe occurs. This has huge implications for our current and future biodiversity, given the unprecedented speed at which species are going extinct owing to the ongoing human-caused climate change.”

{Scientists from the German Primate Center (DPZ), the University of Kentucky, the American Duke Lemur Center and the Université d’Antananarivo in Madagascar have described three new species of mouse lemurs. They live in the South and East of Madagascar and increase the number of known mouse lemur species to 24. As little as 20 years ago, only two species of these small, nocturnal primates were known. New genetic methods and expeditions to remote areas have made the new descriptions possible.}

Mouse lemurs are small, nocturnal primates, which are only found in Madagascar — and they all look very similar with their brown fur and large eyes. Different species can be distinguished reliably only by means of genetic methods. However, how great the difference between two populations has to be to define it as a new species is a source of continuous discussion. “By using new, objective methods to assess genetic differences between individuals, we were able to find independent evidence that these three mouse lemurs represent new species,” says Peter Kappeler, Head of the Behavioral Ecology and Sociobiology Unit at the German Primate Center. In addition, the analysis confirmed the status of the previously described 21 species. “The genetic techniques we used could facilitate species identification, thus also contributing to further new descriptions in other animal groups,” says Peter Kappeler.

Only three years ago, the same research groups had described two new mouse lemur species. The closely related 30g Madame Berthe’s mouse lemur is the smallest primate in the world. Scientists from the German Primate Center discovered it in 1993. Besides improved analytical methods, expeditions to remote and inaccessible forests contribute to the fact that the diversity of these distant relatives of humans becomes better known. “To know the exact distribution area of individual species is necessary to identify functioning protected areas,” says Peter Kappeler, who has conducted research at the field station of the German Primate Center in Madagascar for more than 20 years. “Furthermore, this new information is an important element towards better understanding how biodiversity on Madagascar arose.”

Ganzhorn’s mouse lemur (Microcebus ganzhorni) was named after the ecologist Professor Jörg Ganzhorn from Hamburg University, who has been engaged in research and protection of lemurs for decades. It was Ganzhorn who initiated the field research of the German Primate Center in Madagascar in the 1990s. Also in the Southeast of the “Big Island” Microcebus manitatra is to be found, whose name symbolizes the expansion of the range of a subgroup from western Madagascar. The third member, Microcebus boraha, is named after its location on the Island of Sainte Marie (in Malagasy Nosy Boraha).

According to the “Red List” of the IUCN more than 100 known species of lemurs are threatened by extinction and represent the world’s most endangered group of mammals. Deforestation and hunting are the main causes of the threat to lemurs in one of the poorest countries of the world.

{Forest trees use carbon not only for themselves; they also trade large quantities of it with their neighbours. Botanists from the University of Basel report this in the journal Science. The extensive carbon trade among trees — even among different species — is conducted via symbiotic fungi in the soil.}

It is well known that plants take up carbon dioxide from the air by photosynthesis. The resulting sugar is used to build cellulose, wood pulp (lignin), protein and lipid — the building blocks of plants. While growing, the tree transports sugar from its leaves to the building sites: to the branches, stems, roots and to their symbiotic fungi below ground (mycorrhizal fungi).

Carbon dioxide shower for trees

Dr. Tamir Klein and Prof. Christian Körner of the University of Basel together with Dr. Rolf Siegwolf of the Paul Scherrer Institute (PSI) now report, that this sugar export goes further than previously thought. In a forest near Basel the researchers used a construction crane and a network of fine tubes to flood the crowns of 120 year old and 40 meter tall spruce trees with carbon dioxide that carried a label. The researchers used carbon dioxide that, compared to normal air, contains less of the rare and heavier 13C atom.

While this modification made no difference for the trees, it allowed the botanists to track the carbon through the entire tree using an atomic mass spectrometer. This way they were able to trace the path of the carbon taken up by photosynthesis from the crowns down to the root tips. The researchers found the labelled carbon not only in the roots of the marked spruce trees. The roots of the neighbouring trees also showed the same marker, even though they had not received labelled carbon dioxide. This included trees from other species.

“Forest is more than the sum of its trees”

The only way the carbon could have been exchanged from spruce to beech, pine or larch tree — or vice versa — is by the network of tiny fungal filaments of the shared mycorrhizal fungi. Understory plants which partner up with other types of fungi remained entirely unmarked. The research group called the discovered exchange of large quantities of carbon among completely unrelated tree species in a natural forest “a big surprise.”

According to the researchers, the discovery questions the concept of tree individuality with regard to the single largest constituent of the biosphere, tree carbon. Furthermore, the results of the study funded by the Swiss National Science Foundation add a new dimension to the role of mycorrhizal fungi in forests. “Evidently the forest is more than the sum of its trees,” comments Prof. Christian Körner the findings.