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September 2014
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Hadrosaur with huge nose discovered

Call it the Jimmy Durante of dinosaurs — a newly discovered hadrosaur with a truly distinctive nasal profile. The new dinosaur, named Rhinorex condrupus by paleontologists, lived in what is now Utah approximately 75 million years ago during the Late Cretaceous period.
The newly discovered hadrosaur, Rhinorex condrupus, has a truly distinctive nasal profile. Credit: Terry Gates

The newly discovered hadrosaur, Rhinorex condrupus, has a truly distinctive nasal profile.
Credit: Terry Gates

Rhinorex, which translates roughly into “King Nose,” was a plant-eater and a close relative of other Cretaceous hadrosaurs like Parasaurolophus and Edmontosaurus. Hadrosaurs are usually identified by bony crests that extended from the skull, although Edmontosaurus doesn’t have such a hard crest (paleontologists have discovered that it had a fleshy crest). Rhinorex also lacks a crest on the top of its head; instead, this new dinosaur has a huge nose.

Terry Gates, a joint postdoctoral researcher with NC State and the North Carolina Museum of Natural Sciences, and colleague Rodney Sheetz from the Brigham Young Museum of Paleontology, came across the fossil in storage at BYU. First excavated in the 1990s from Utah’s Neslen formation, Rhinorex had been studied primarily for its well-preserved skin impressions. When Gates and Sheetz reconstructed the skull, they realized that they had a new species.

“We had almost the entire skull, which was wonderful,” Gates says, “but the preparation was very difficult. It took two years to dig the fossil out of the sandstone it was embedded in — it was like digging a dinosaur skull out of a concrete driveway.”

Based on the recovered bones, Gates estimates that Rhinorex was about 30 feet long and weighed over 8,500 lbs. It lived in a swampy estuarial environment, about 50 miles from the coast. Rhinorex is the only complete hadrosaur fossil from the Neslen site, and it helps fill in some gaps about habitat segregation during the Late Cretaceous.

“We’ve found other hadrosaurs from the same time period but located about 200 miles farther south that are adapted to a different environment,” Gates says. “This discovery gives us a geographic snapshot of the Cretaceous, and helps us place contemporary species in their correct time and place. Rhinorex also helps us further fill in the hadrosaur family tree.”

When asked how Rhinorex may have benefitted from a large nose Gates said, “The purpose of such a big nose is still a mystery. If this dinosaur is anything like its relatives then it likely did not have a super sense of smell; but maybe the nose was used as a means of attracting mates, recognizing members of its species, or even as a large attachment for a plant-smashing beak. We are already sniffing out answers to these questions.”

Reference: Terry A. Gates, Rodney Scheetz. A new saurolophine hadrosaurid (Dinosauria: Ornithopoda) from the Campanian of Utah, North America. Journal of Systematic Palaeontology, 2014; 1 DOI: 10.1080/14772019.2014.950614

Nature of war: Chimps inherently violent

Of all of the world’s species, humans and chimpanzees are some of the only species to coordinate attacks on their own members. Since Jane Goodall introduced lethal inter-community killings, primatologists have debated the concept of warfare in this genus. New research from an international coalition of ape researchers has shed new light on the subject, suggesting that human encroachment and interference is not, as previous researchers have claimed, an influential predictor of chimp-on-chimp aggression.
The Ngogo males have just killed a male from a neighboring group. After the male is dead, one of the Ngogo males leaps on the body of the dead animal. Credit: Image courtesy of John Mitani

The Ngogo males have just killed a male from a neighboring group. After the male is dead, one of the Ngogo males leaps on the body of the dead animal.
Credit: Image courtesy of John Mitani

New research from an international coalition of ape researchers, published September 18 in the journal Nature, has shed new light on the subject, suggesting that human encroachment and interference is not, as previous researchers have claimed, an influential predictor of chimp-on-chimp aggression.

The study began as a response to a growing number of commentators claiming that chimpanzee violence was caused by human impacts. “This is an important question to get right. If we are using chimpanzees as a model for understanding human violence, we need to know what really causes chimpanzees to be violent,” said University of Minnesota researcher Michael L. Wilson, lead author on the study.

“Humans have long impacted African tropical forests and chimpanzees, and one of the long-standing questions is if human disturbance is an underlying factor causing the lethal aggression observed,” explained co-author David Morgan, PhD, research fellow with the Lester E Fisher Center for the Study and Conservation of Apes at Lincoln Park Zoo in Chicago. Morgan has studied chimpanzees deep in the forests of Republic of Congo for 14 years. “A key take-away from this research is that human influence does not spur increased aggression within or between chimpanzee communities.”

A team of 30 ape researchers assembled extensive data sets spanning five decades of research gathered from 18 chimpanzee communities experiencing varying degrees of human influence. In all, data included pattern analysis of 152 killings by chimpanzees. The key findings indicate that a majority of violent attackers and victims of attack are male chimpanzees, and the information is consistent with the theory that these acts of violence are driven by adaptive fitness benefits rather than human impacts.

“Wild chimpanzee communities are often divided into two broad categories depending on whether they exist in pristine or human disturbed environments,” explained Morgan. “In reality, however, human disturbance can occur along a continuum and study sites included in this investigation spanned the spectrum. We found human impact did not predict the rate of killing among communities.

“The more we learn about chimpanzee aggression and factors that trigger lethal attacks among chimpanzees, the more prepared park managers and government officials will be in addressing and mitigating risks to populations particularly with changing land use by humans in chimpanzee habitat,” explained Morgan.

Reference: Michael L. Wilson, Christophe Boesch, Barbara Fruth, Takeshi Furuichi, Ian C. Gilby, Chie Hashimoto, Catherine L. Hobaiter, Gottfried Hohmann, Noriko Itoh, Kathelijne Koops, Julia N. Lloyd, Tetsuro Matsuzawa, John C. Mitani, Deus C. Mjungu, David Morgan, Martin N. Muller, Roger Mundry, Michio Nakamura, Jill Pruetz, Anne E. Pusey, Julia Riedel, Crickette Sanz, Anne M. Schel, Nicole Simmons, Michel Waller, David P. Watts, Frances White, Roman M. Wittig, Klaus Zuberbühler, Richard W. Wrangham. Lethal aggression in Pan is better explained by adaptive strategies than human impacts. Nature, 2014; 513 (7518): 414 DOI: 10.1038/nature13727

Europeans descended from at least 3, not 2, groups of ancient humans

Previous work suggested that Europeans descended from two ancestral groups: indigenous hunter-gatherers and early European farmers. This new study shows that there was also a third ancestral group, the Ancient North Eurasians, who contributed genetic material to almost all present-day Europeans. The research also reveals an even older lineage, the Basal Eurasians.
This skull of a 7,000-year-old German farmer was among the ancient human bones that revealed more about the genetic heritage of present-day Europeans. Credit: Joanna Drath/University of Tübingen

This skull of a 7,000-year-old German farmer was among the ancient human bones that revealed more about the genetic heritage of present-day Europeans.
Credit: Joanna Drath/University of Tübingen

Genetic and archaeological research in the last 10 years has revealed that almost all present-day Europeans descend from the mixing of these two ancient populations. But it turns out that’s not the full story.

Researchers at Harvard Medical School and the University of Tübingen in Germany have now documented a genetic contribution from a third ancestor: Ancient North Eurasians. This group appears to have contributed DNA to present-day Europeans as well as to the people who travelled across the Bering Strait into the Americas more than 15,000 years ago.

“Prior to this paper, the models we had for European ancestry were two-way mixtures. We show that there are three groups,” said David Reich, professor of genetics at HMS and co-senior author of the study.

“This also explains the recently discovered genetic connection between Europeans and Native Americans,” Reich added. “The same Ancient North Eurasian group contributed to both of them.”

The research team also discovered that ancient Near Eastern farmers and their European descendants can trace much of their ancestry to a previously unknown, even older lineage called the Basal Eurasians.

The study is published Sept. 18 in Nature.

Peering into the past

To probe the ongoing mystery of Europeans’ heritage and their relationships to the rest of the world, the international research team — including co-senior author Johannes Krause, professor of archaeo- and paleogenetics at the University of Tübingen and co-director of the new Max Planck Institute for History and the Sciences in Jena, Germany — collected and sequenced the DNA of more than 2,300 present-day people from around the world and of nine ancient humans from Sweden, Luxembourg and Germany.

The ancient bones came from eight hunter-gatherers who lived about 8,000 years ago, before the arrival of farming, and one farmer from about 7,000 years ago.

The researchers also incorporated into their study genetic sequences previously gathered from ancient humans of the same time period, including early farmers such as Ötzi “the Iceman.”

“There was a sharp genetic transition between the hunter-gatherers and the farmers, reflecting a major movement of new people into Europe from the Near East,” said Reich.

Ancient North Eurasian DNA wasn’t found in either the hunter-gatherers or the early farmers, suggesting the Ancient North Eurasians arrived in the area later, he said.

“Nearly all Europeans have ancestry from all three ancestral groups,” said Iosif Lazaridis, a research fellow in genetics in Reich’s lab and first author of the paper. “Differences between them are due to the relative proportions of ancestry. Northern Europeans have more hunter-gatherer ancestry — up to about 50 percent in Lithuanians — and Southern Europeans have more farmer ancestry.”

Lazaridis added, “The Ancient North Eurasian ancestry is proportionally the smallest component everywhere in Europe, never more than 20 percent, but we find it in nearly every European group we’ve studied and also in populations from the Caucasus and Near East. A profound transformation must have taken place in West Eurasia” after farming arrived.

When this research was conducted, Ancient North Eurasians were a “ghost population” — an ancient group known only through the traces it left in the DNA of present-day people. Then, in January, a separate group of archaeologists found the physical remains of two Ancient North Eurasians in Siberia. Now, said Reich, “We can study how they’re related to other populations.”

Room for more

The team was able to go only so far in its analysis because of the limited number of ancient DNA samples. Reich thinks there could easily be more than three ancient groups who contributed to today’s European genetic profile.

He and his colleagues found that the three-way model doesn’t tell the whole story for certain regions of Europe. Mediterranean groups such as the Maltese, as well as Ashkenazi Jews, had more Near East ancestry than anticipated, while far northeastern Europeans such as Finns and the Saami, as well as some northern Russians, had more East Asian ancestry in the mix.

The most surprising part of the project for Reich, however, was the discovery of the Basal Eurasians.

“This deep lineage of non-African ancestry branched off before all the other non-Africans branched off from one another,” he said. “Before Australian Aborigines and New Guineans and South Indians and Native Americans and other indigenous hunter-gatherers split, they split from Basal Eurasians. This reconciled some contradictory pieces of information for us.”

Next, the team wants to figure out when the Ancient North Eurasians arrived in Europe and to find ancient DNA from the Basal Eurasians.

“We are only starting to understand the complex genetic relationship of our ancestors,” said co-author Krause. “Only more genetic data from ancient human remains will allow us to disentangle our prehistoric past.”

“There are important open questions about how the present-day people of the world got to where they are,” said Reich, who is a Howard Hughes Medical Investigator. “The traditional way geneticists study this is by analyzing present-day people, but this is very hard because present-day people reflect many layers of mixture and migration.

“Ancient DNA sequencing is a powerful technology that allows you to go back to the places and periods where important demographic events occurred,” he said. “It’s a great new opportunity to learn about human history.”

Reference: Iosif Lazaridis, Nick Patterson, Alissa Mittnik, Gabriel Renaud, Swapan Mallick, Karola Kirsanow, Peter H. Sudmant, Joshua G. Schraiber, Sergi Castellano, Mark Lipson, Bonnie Berger, Christos Economou, Ruth Bollongino, Qiaomei Fu, Kirsten I. Bos, Susanne Nordenfelt, Heng Li, Cesare de Filippo, Kay Prüfer, Susanna Sawyer, Cosimo Posth, Wolfgang Haak, Fredrik Hallgren, Elin Fornander, Nadin Rohland, Dominique Delsate, Michael Francken, Jean-Michel Guinet, Joachim Wahl, George Ayodo, Hamza A. Babiker, Graciela Bailliet, Elena Balanovska, Oleg Balanovsky, Ramiro Barrantes, Gabriel Bedoya, Haim Ben-Ami, Judit Bene, Fouad Berrada, Claudio M. Bravi, Francesca Brisighelli, George B. J. Busby, Francesco Cali, Mikhail Churnosov, David E. C. Cole, Daniel Corach, Larissa Damba, George van Driem, Stanislav Dryomov, Jean-Michel Dugoujon, Sardana A. Fedorova, Irene Gallego Romero, Marina Gubina, Michael Hammer, Brenna M. Henn, Tor Hervig, Ugur Hodoglugil, Aashish R. Jha, Sena Karachanak-Yankova, Rita Khusainova, Elza Khusnutdinova, Rick Kittles, Toomas Kivisild, William Klitz, Vaidutis Kučinskas, Alena Kushniarevich, Leila Laredj, Sergey Litvinov, Theologos Loukidis, Robert W. Mahley, Béla Melegh, Ene Metspalu, Julio Molina, Joanna Mountain, Klemetti Näkkäläjärvi, Desislava Nesheva, Thomas Nyambo, Ludmila Osipova, Jüri Parik, Fedor Platonov, Olga Posukh, Valentino Romano, Francisco Rothhammer, Igor Rudan, Ruslan Ruizbakiev, Hovhannes Sahakyan, Antti Sajantila, Antonio Salas, Elena B. Starikovskaya, Ayele Tarekegn, Draga Toncheva, Shahlo Turdikulova, Ingrida Uktveryte, Olga Utevska, René Vasquez, Mercedes Villena, Mikhail Voevoda, Cheryl A. Winkler, Levon Yepiskoposyan, Pierre Zalloua, Tatijana Zemunik, Alan Cooper, Cristian Capelli, Mark G. Thomas, Andres Ruiz-Linares, Sarah A. Tishkoff, Lalji Singh, Kumarasamy Thangaraj, Richard Villems, David Comas, Rem Sukernik, Mait Metspalu, Matthias Meyer, Evan E. Eichler, Joachim Burger, Montgomery Slatkin, Svante Pääbo, Janet Kelso, David Reich, Johannes Krause. Ancient human genomes suggest three ancestral populations for present-day Europeans. Nature, 2014; 513 (7518): 409 DOI: 10.1038/nature13673

Pulse of a dead star powers intense gamma rays

NASA’s Nuclear Spectroscopic Telescope Array, or NuSTAR, is helping to untangle the mystery of what powers high-energy gamma rays emanating from supernova. The observatory’s high-energy X-ray eyes were able to peer into a particular site of powerful gamma rays and confirm the source: A spinning, dead star called a pulsar.
The blue dot in this image marks the spot of an energetic pulsar -- the magnetic, spinning core of star that blew up in a supernova explosion. Credit: NASA/JPL-Caltech/SAO

The blue dot in this image marks the spot of an energetic pulsar — the magnetic, spinning core of star that blew up in a supernova explosion.
Credit: NASA/JPL-Caltech/SAO

When the most massive stars explode as supernovas, they don’t fade into the night, but sometimes glow ferociously with high-energy gamma rays. What powers these energetic stellar remains?

NASA’s Nuclear Spectroscopic Telescope Array, or NuSTAR, is helping to untangle the mystery. The observatory’s high-energy X-ray eyes were able to peer into a particular site of powerful gamma rays and confirm the source: A spinning, dead star called a pulsar. Pulsars are one of several types of stellar remnants that are left over when stars blow up in supernova explosions.

This is not the first time pulsars have been discovered to be the culprits behind intense gamma rays, but NuSTAR has helped in a case that was tougher to crack due to the distance of the object in question. NuSTAR joins NASA’s Chandra X-ray Observatory and Fermi Gamma-ray Space Telescope, and the High Energy Stereoscopic System (H.E.S.S.) in Namibia, each with its own unique strengths, to better understand the evolution of these not-so-peaceful dead stars.

“The energy from this corpse of a star is enough to power the gamma-ray luminosity we are seeing,” said Eric Gotthelf of Columbia University, New York. Gotthelf explained that while pulsars are often behind these gamma rays in our galaxy, other sources can be as well, including the outer shells of the supernova remnants, X-ray binary stars and star-formation regions. Gotthelf is lead author of a new paper describing the findings in the Astrophysical Journal.

In recent years, the Max-Planck Institute for Astronomy’s H.E.S.S. experiment has identified more than 80 incredibly powerful sites of gamma rays, called high-energy gamma-ray sources, in our Milky Way. Most of these have been associated with prior supernova explosions, but for many, the primary source of observed gamma rays remains unknown.

The gamma-ray source pinpointed in this new study, called HESS J1640-465, is one of the most luminous discovered so far. It was already known to be linked with a supernova remnant, but the source of its power was unclear. While data from Chandra and the European Space Agency’s XMM-Newton telescopes hinted that the power source was a pulsar, intervening clouds of gas blocked the view, making it difficult to see.

NuSTAR complements Chandra and XMM-Newton in its capability to detect higher-energy range of X-rays that can, in fact, penetrate through this intervening gas. In addition, the NuSTAR telescope can measure rapid X-ray pulsations with fine precision. In this particular case, NuSTAR was able to capture high-energy X-rays coming at regular fast-paced pulses from HESS J1640-465. These data led to the discovery of PSR J1640-4631, a pulsar spinning five times per second — and the ultimate power source of both the high-energy X-rays and gamma rays.

How does the pulsar produce the high-energy rays? The pulsar’s strong magnetic fields generate powerful electric fields that accelerate charged particles near the surface to incredible speeds approaching that of light. The fast-moving particles then interact with the magnetic fields to produce the powerful beams of high-energy gamma rays and X-rays.

“The discovery of a pulsar engine powering HESS J1640-465 allows astronomers to test models for the underlying physics that result in the extraordinary energies generated by these rare gamma-rays sources,” said Gotthelf.

“Perhaps other luminous gamma-ray sources harbor pulsars that we can’t detect,” said Victoria Kaspi of McGill University, Montreal, Canada, a co-author on the study. “With NuSTAR, we may be able to find more hidden pulsars.”

The new data also allowed astronomers to measure the rate at which the pulsar slows, or spins down (about 30 microseconds per year), as well as how this spin-down rate varies over time. The answers will help researchers understand how these spinning magnets — the cores of dead stars — can be the source of such extreme radiation in our galaxy.

Reference: E. V. Gotthelf, J. A. Tomsick, J. P. Halpern, J. D. Gelfand, F. A. Harrison, S. E. Boggs, F. E. Christensen, W. W. Craig, J. C. Hailey, V. M. Kaspi, D. K. Stern, W. W. Zhang. NuSTAR Discovery of a Young, Energetic Pulsar Associated with the Luminous Gamma-Ray Source HESS J1640–465. The Astrophysical Journal, 2014; 788 (2): 155 DOI: 10.1088/0004-637X/788/2/155

Each tree species has unique bacterial identity, microbiome research shows

Each tree species has its own bacterial identity. That’s the conclusion of researchers who studied the genetic fingerprints of bacteria on 57 species of trees growing on a Panamanian island.
Lush forest (stock image). "This study demonstrates for the first time that host plants from different plant families and with different ecological strategies possess very different microbial communities on their leaves," said lead author Steven W. Kembel. Credit: © Les Cunliffe

Lush forest (stock image). “This study demonstrates for the first time that host plants from different plant families and with different ecological strategies possess very different microbial communities on their leaves,” said lead author Steven W. Kembel.
Credit: © Les Cunliffe

“This study demonstrates for the first time that host plants from different plant families and with different ecological strategies possess very different microbial communities on their leaves,” said lead author Steven W. Kembel, a former postdoctoral researcher in the UO’s Institute of Ecology and Evolution who is now a professor of biological sciences at the University of Quebec at Montreal.

For the research — published this week in the online Early Edition of the Proceedings of the National Academy of Sciences — researchers gathered bacterial samples from 57 of the more than 450 tree species growing in a lowland tropical forest on Barro Colorado Island, Panama.

Using DNA sequencing technology housed at the UO’s Genomics Core Facility, scientists sequenced the bacterial 16S ribosomal RNA gene isolated from the samples. That gene, which biologists call a barcode gene, allowed researchers to identify and measure the diversity of bacteria based on millions of DNA fragments produced from bacterial communities collected from the surfaces of leaves, said Jessica Green, a professor at both the UO and Santa Fe Institute.

“Some bacteria were very abundant and present on every leaf in the forest, while others were rare and only found on the leaves of a single host species,” Kembel said. “Each tree species of tree possessed a distinctive community of bacteria on its leaves.”

In the world of microbiology, plant leaves are considered to be a habitat known as the phyllosphere. They are host to millions of bacteria, Kembel said. “These bacteria can have important effects — both positive and negative — on the health and functioning of their host plants,” he said. “For example, while some bacteria on leaves cause disease, others may protect the plant against pathogens or produce hormones that increase plant growth rates.”

In the animal microbiome, the researchers noted, studies comparing large numbers of species have shown that host diet — for example, herbivory versus carnivory — has a large effect on the structure of microbial communities in their guts. The new study, Kembel and Green said, provides a comparable understanding of the host attributes that explain patterns of microbial diversity in the plant microbiome.

“We found that the abundance of some bacterial taxa was correlated with the growth, mortality, and function of the host,” Kembel said. These included bacteria involved in nitrogen fixing and the consumption of methane, as well as bacteria linked to soil and water.

Dominating the bacterial communities were a core microbiome of taxa including Actinobacteria, Alpha-, Beta- and Gamma-Proteobacteria and Sphingobacteria. Some types of bacteria, the researcher found, were more abundant when growing on the leaves of fast-growing or slow-growing tree species, or on leaves with different concentrations of elements such as nitrogen or phosphorus.

“Because of the importance of the microbiome for the growth and function of the host, understanding the factors that influence bacteria on the leaves of different trees could have important implications for our ability to model and conserve biological diversity and ecosystem function,” Kembel said. “Ultimately, we hope that understanding the factors that explain variation in bacterial abundances across host species will help us better manage biological diversity in forests and the health and function of forest ecosystems.”

Reference: S. W. Kembel, T. K. O’Connor, H. K. Arnold, S. P. Hubbell, S. J. Wright, J. L. Green. Relationships between phyllosphere bacterial communities and plant functional traits in a neotropical forest. Proceedings of the National Academy of Sciences, 2014; DOI: 10.1073/pnas.1216057111

219 million stars: Astronomers release most detailed catalog ever made of the visible Milky Way

A new catalog of the visible part of the northern part of our home Galaxy, the Milky Way, includes no fewer than 219 million stars. From dark sky sites on Earth, the Milky Way appears as a glowing band stretching across the sky. To astronomers, it is the disk of our own galaxy, a system stretching across 100,000 light-years, seen edge-on from our vantage point orbiting the Sun. The disk contains the majority of the stars in the galaxy, including the Sun, and the densest concentrations of dust and gas.
A density map of part of the Milky Way disk, constructed from IPHAS data. The axes show galactic latitude and longitude, coordinates that relate to the position of the centre of the galaxy. The mapped data are the counts of stars detected in i, the longer (redder) wavelength broad band of the survey, down to a faint limit of 19th magnitude. Although this is just a small section of the full map, it portrays in exquisite detail the complex patterns of obscuration due to interstellar dust. Credit: Hywel Farnhill, University of Hertfordshire

A density map of part of the Milky Way disk, constructed from IPHAS data. The axes show galactic latitude and longitude, coordinates that relate to the position of the centre of the galaxy. The mapped data are the counts of stars detected in i, the longer (redder) wavelength broad band of the survey, down to a faint limit of 19th magnitude. Although this is just a small section of the full map, it portrays in exquisite detail the complex patterns of obscuration due to interstellar dust.
Credit: Hywel Farnhill, University of Hertfordshire

The unaided human eye struggles to distinguish individual objects in this crowded region of the sky, but the 2.5-m mirror of the INT enabled the scientists to resolve and chart 219 million separate stars. The INT programme charted all the stars brighter than 20th magnitude — or 1 million times fainter than can be seen with the human eye.

Using the catalogue, the scientists have put together an extraordinarily detailed map of the disk of the Galaxy that shows how the density of stars varies, giving them a new and vivid insight into the structure of this vast system of stars, gas and dust.

The image included here, a cut-out from a stellar density map mined directly from the released catalogue, illustrates the new view obtained. The Turner-like brush strokes of dust shadows would grace the wall of any art gallery. Maps like these also stand as useful tests of new-generation models for the Milky Way.

The production of the catalogue, IPHAS DR2 (the second release from the survey programme The INT Photometric H-alpha Survey of the Northern Galactic Plane or IPHAS), is an example of modern astronomy’s exploitation of ‘big data’ — it contains information on the 219 million detected objects, each of which is summarised in 99 attributes.

With this catalogue release, the team are offering the world community free access to measurements taken through two broad band filters capturing light at the red end of the visible spectrum, and in a narrowband capturing the brightest hydrogen emission line, H-alpha. The inclusion of H-alpha also enables exquisite imaging of the nebulae (glowing clouds of gas) found in greatest number within the disk of the Milky Way. The stellar density map illustrated here is derived from the longest (reddest) wavelength band in which the darkening effect of the dust is moderated in a way that brings out more of its structural detail, compared to maps built at shorter (bluer) wavelengths.

Reference: Geert Barentsen, H. J. Farnhill, J. E. Drew, E. A. González-Solares, R. Greimel, M. J. Irwin, B. Miszalski, C. Ruhland, P. Groot, A. Mampaso, S. E. Sale, A. A. Henden, A. Aungwerojwit, M. J. Barlow, P. J. Carter, R. L. M. Corradi, J. J. Drake, J. Eislöffel, J. Fabregat, B. T. Gänsicke, N. P. Gentile Fusillo, S. Greiss, A. S. Hales, S. Hodgkin, L. Huckvale, J. Irwin, R. King, C. Knigge, T. Kupfer, E. Lagadec, D. J. Lennon, J. R. Lewis, M. Mohr-Smith, R. A. H. Morris, T. Naylor, Q. A. Parker, S. Phillipps, S. Pyrzas, R. Raddi, G. H. A. Roelofs, P. Rodríguez-Gil, L. Sabin, S. Scaringi, D. Steeghs, J. Suso, R. Tata, Y. C. Unruh, J. van Roestel, K. Viironen, J. S. Vink, N. A. Walton, N. J. Wright, and A. A. Zijlstra. The second data release of the INT Photometric Hα Survey of the Northern Galactic Plane (IPHAS DR2). MNRAS, September 15, 2014 DOI: 10.1093/mnras/stu1651

Impact that doomed the dinosaurs helped the forests bloom

Some 66 million years ago, a 10-km diameter chunk of rock hit the Yucatan peninsula with the force of 100 teratons of TNT. It left a crater more than 150 km across, and the resulting megatsunami, wildfires, global earthquakes and volcanism are widely accepted to have wiped out the dinosaurs and made way for the rise of the mammals. But what happened to the plants on which the dinosaurs fed?
Seen here is a Late Cretaceous specimen from the Hell Creek Formation, morphotype HC62, taxon Rhamnus cleburni. Specimens are housed at the Denver Museum of Nature and Science in Denver, Colorado. Credit: Benjamin Blonder, Doi: 10.1371/journal.pbio.1001949, CC

Seen here is a Late Cretaceous specimen from the Hell Creek Formation, morphotype HC62, taxon Rhamnus cleburni. Specimens are housed at the Denver Museum of Nature and Science in Denver, Colorado.
Credit: Benjamin Blonder, Doi: 10.1371/journal.pbio.1001949, CC

A new study led by researchers from the University of Arizona reveals that the impact that spelled doom for the dinosaurs also decimated the evergreen flowering plants to a much greater extent than their deciduous peers. They hypothesize that the properties of deciduous plants made them better able to respond rapidly to chaotically varying post-apocalyptic climate conditions. The results are publishing on September 16 in the open access journal PLOS Biology.

Applying biomechanical formulae to a treasure trove of thousands of fossilized leaves of angiosperms — flowering plants excluding conifers — the team was able to reconstruct the ecology of a diverse plant community thriving during a 2.2 million-year period spanning the cataclysmic impact event, believed to have wiped out more than half of plant species living at the time. The fossilized leaf samples span the last 1,400,000 years of the Cretaceous and the first 800,000 of the Paleogene.

The researchers found evidence that after the impact, fast-growing, deciduous angiosperms had replaced their slow-growing, evergreen peers to a large extent. Living examples of evergreen angiosperms, such as holly and ivy, tend to prefer shade, don’t grow very fast and sport dark-colored leaves.

“When you look at forests around the world today, you don’t see many forests dominated by evergreen flowering plants,” said the study’s lead author, Benjamin Blonder. “Instead, they are dominated by deciduous species, plants that lose their leaves at some point during the year.”

Blonder and his colleagues studied a total of about 1,000 fossilized plant leaves collected from a location in southern North Dakota, embedded in rock layers known as the Hell Creek Formation, which at the end of the Cretaceous was a lowland floodplain crisscrossed by river channels. The collection consists of more than 10,000 identified plant fossils and is housed primarily at the Denver Museum of Nature and Science. “When you hold one of those leaves that is so exquisitely preserved in your hand knowing it’s 66 million years old, it’s a humbling feeling,” said Blonder.

“If you think about a mass extinction caused by catastrophic event such as a meteorite impacting Earth, you might imagine all species are equally likely to die,” Blonder said. “Survival of the fittest doesn’t apply — the impact is like a reset button. The alternative hypothesis, however, is that some species had properties that enabled them to survive.

“Our study provides evidence of a dramatic shift from slow-growing plants to fast-growing species,” he said. “This tells us that the extinction was not random, and the way in which a plant acquires resources predicts how it can respond to a major disturbance. And potentially this also tells us why we find that modern forests are generally deciduous and not evergreen.”

Previously, other scientists found evidence of a dramatic drop in temperature caused by dust from the impact. “The hypothesis is that the impact winter introduced a very variable climate,” Blonder said. “That would have favored plants that grew quickly and could take advantage of changing conditions, such as deciduous plants.”

“We measured the mass of a given leaf in relation to its area, which tells us whether the leaf was a chunky, expensive one to make for the plant, or whether it was a more flimsy, cheap one,” Blonder explained. “In other words, how much carbon the plant had invested in the leaf.” In addition the researchers measured the density of the leaves’ vein networks, a measure of the amount of water a plant can transpire and the rate at which it can acquire carbon.

“There is a spectrum between fast- and slow-growing species,” said Blonder. “There is the ‘live fast, die young’ strategy and there is the ‘slow but steady’ strategy. You could compare it to financial strategies investing in stocks versus bonds.” The analyses revealed that while slow-growing evergreens dominated the plant assemblages before the extinction event, fast-growing flowering species had taken their places afterward.

Reference: Benjamin Blonder, Dana L. Royer, Kirk R. Johnson, Ian Miller, Brian J. Enquist. Plant Ecological Strategies Shift Across the Cretaceous–Paleogene Boundary. PLoS Biology, 2014; 12 (9): e1001949 DOI: 10.1371/journal.pbio.1001949

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