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Breakup of supercontinent Pangea cooled mantle and thinned crust

Researchers at the University of Texas Institute for Geophysics used the location of seismic refraction data (circles) and mantle hotspots (white stars) to examine whether mid-plate volcanism substantially influenced the thickness of aged ocean crust. The modern mid-ocean ridge system is marked by a yellow line. Areas in violet outline large igneous provinces.
Credit: The University of Texas at Austin Jackson School of Geosciences

The oceanic crust produced by the Earth today is significantly thinner than crust made 170 million years ago during the time of the supercontinent Pangea, according to University of Texas at Austin researchers.

The thinning is related to the cooling of Earth’s interior prompted by the splitting of the supercontinent Pangaea, which broke up into the continents that we have today, said Harm Van Avendonk, the lead author of the study and a senior research scientist at The University of Texas Institute for Geophysics. The findings, published in Nature Geosciences on Dec. 12, shed light on how plate tectonics has influenced the cooling of the Earth’s mantle throughout geologic history.

“What we think is happening is that the supercontinent was like an insulating blanket,” Van Avendonk said. “So when these continents started opening up and the deeper mantle was exposed, more or less, to the atmosphere and the ocean it started cooling much faster.”

All authors are from the University of Texas Institute for Geophysics (UTIG), a research unit of the Jackson School of Geosciences.

The mantle is the very hot, but mostly solid, layer of rock between the Earth’s crust and core. Magma from the mantle forms oceanic crust when it rises from the mantle to the surface at spreading centers and cools into the rock that forms the very bottom of the seafloor. Since about 2.5 billion years ago, the mantle has been cooling — a phenomenon that doesn’t influence the climate on the surface of the Earth and has nothing to do with the issue of short-term human-made climate change. This study suggests that since the breakup of Pangea, the cooling rate of the mantle has increased from 6-11 degrees Celsius per 100 million years to 15-20 degrees per 100 million years. Since cooler mantle temperatures generally produce less magma, it’s a trend that’s making modern day ocean crust thinner.

“It’s important to note the Earth seems to be cooling a lot faster now than it has been over its lifetime,” Van Avendonk said. “The current state of the Earth, where we have a lot of plate tectonic events, this allows the Earth to cool much more efficiently than it did in the past.”

The research that led to the connection between the splitting of the supercontinent and crust thickness started when Van Avendock and Ph.D. student Jennifer Harding, a study co-author, noticed an unexpected trend when studying existing data from young and old seafloor. They analyzed 234 measurements of crustal thickness from around the world and found that, on a global scale, the oldest ocean crust examined — 170 million year old rock created in the Jurassic — is about one mile thicker than the crust that’s being produced today.

“It’s something that Jenny and I found, more or less, by accident,” Van Avendonk said.

The link between crust thickness and age prompted two possible explanations — both related to the fact that hotter mantle tends to make more magma: Mantle hot spots — highly volcanic regions, such as the Hawaiian Islands and Iceland — could have thickened the old crust by covering it in layers of lava at a later time. Or, the mantle was hotter in the Jurassic than it is now.

Van Avendonk mentioned this problem during a casual conversation with Joshua “Bud” Davis, a Ph.D. student in UTIG’s plate tectonics research group and co-author, who said that the group could investigate both of the explanations using computer models of plate movement since the Jurassic and a global database of hotspots.

The analysis ruled out the hot spot theory — thick layers of old crust formed just as easily at distances greater than 600 miles from hotspots, a distance that the researchers judged was outside the influence of the hotspots. In contrast, the analysis supported the hypothesis of mantle heating during the age of Pangea, and mantle cooling after the breakup of the supercontinent.

The finding that splitting up Pangea cooled the mantle is important because it gives a more nuanced view of the mantle temperature that influences tectonics on Earth, Van Avendonk said. The researchers also note that the study illustrates the success that can come from spontaneous collaboration and leveraging basic research on a global scale.

“A cool part of this study is that it didn’t need funding,” Harding said. “We went through all the literature, and collected all the data ourselves. There’s always more information out there.”

Reference:
Harm J. A. Van Avendonk, Joshua K. Davis, Jennifer L. Harding, Lawrence A. Lawver. Decrease in oceanic crustal thickness since the breakup of Pangaea. Nature Geoscience, 2016; DOI: 10.1038/ngeo2849

Note: The above post is reprinted from materials provided by University of Texas at Austin.

Earth’s magnetic fields could track ocean heat

NASA scientists are developing a new way to use satellite observations of magnetic fields to measure heat stored in the ocean. Credit: NASA Goddard Space Flight Center

As Earth warms, much of the extra heat is stored in the planet’s ocean—but monitoring the magnitude of that heat content is a difficult task.

A surprising feature of the tides could help, however. Scientists at NASA’s Goddard Space Flight Center in Greenbelt, Maryland, are developing a new way to use satellite observations of magnetic fields to measure heat stored in the ocean.

“If you’re concerned about understanding global warming, or Earth’s energy balance, a big unknown is what’s going into the ocean,” said Robert Tyler, a research scientist at Goddard. “We know the surfaces of the oceans are heating up, but we don’t have a good handle on how much heat is being stored deep in the ocean.”

Despite the significance of ocean heat to Earth’s climate, it remains a variable that has substantial uncertainty when scientists measure it globally. Current measurements are made mainly by Argo floats, but these do not provide complete coverage in time or space. If it is successful, this new method could be the first to provide global ocean heat measurements, integrated over all depths, using satellite observations.

Tyler’s method depends on several geophysical features of the ocean. Seawater is a good electrical conductor, so as saltwater sloshes around the ocean basins it causes slight fluctuations in Earth’s magnetic field lines. The ocean flow attempts to drag the field lines around, Tyler said. The resulting magnetic fluctuations are relatively small, but have been detected from an increasing number of events including swells, eddies, tsunamis and tides.

“The recent launch of the European Space Agency’s Swarm satellites, and their magnetic survey, are providing unprecedented observational data of the magnetic fluctuations,” Tyler said. “With this comes new opportunities.”

Researchers know where and when the tides are moving ocean water, and with the high-resolution data from the Swarm satellites, they can pick out the magnetic fluctuations due to these regular ocean movements.

That’s where another geophysical feature comes in. The magnetic fluctuations of the tides depend on the electrical conductivity of the water—and the electrical conductivity of the water depends on its temperature.

For Tyler, the question then is: “By monitoring these magnetic fluctuations, can we monitor the ocean temperature?”

At the American Geophysical Union meeting in San Francisco this week, Tyler and collaborator Terence Sabaka, also at Goddard, presented the first results. They provide a key proof-of-concept of the method by demonstrating that global ocean heat content can be recovered from “noise-free” ocean tidal magnetic signals generated by a computer model. When they try to do this with the “noisy” observed signals, it doesn’t yet provide the accuracy needed to monitor changes in the heat content.

But, Tyler said, there is much room for improvement in how the data are processed and modeled, and the Swarm satellites continue to collect magnetic data. This is a first attempt at using satellite magnetic data to monitor ocean heat, he said, and there is still much more to be done before the technique could successfully resolve this key variable. For example, by identifying fluctuations caused by other ocean movements, like eddies or other tidal components, scientists can extract even more information and get more refined measurements of ocean heat content and how it’s changing.

More than 90 percent of the excess heat in the Earth system goes into the ocean, said Tim Boyer, a scientist with the National Oceanic and Atmospheric Administration’s National Centers for Environmental Information. Scientists currently monitor ocean heat with shipboard measurements and Argo floats. While these measurements and others have seen a steady increase in heat since 1955, researchers still need more complete information, he said.

“Even with the massive effort with the Argo floats, we still don’t have as much coverage of the ocean as we would really like in order to lower the uncertainties,” Boyer said. “If you’re able to measure global ocean heat content directly and completely from satellites, that would be fantastic.”

Changing ocean temperatures have impacts that stretch across the globe. In Antarctica, floating sections of the ice sheet are retreating in ways that can’t be explained only by changes in atmospheric temperatures, said Catherine Walker, an ice scientist at NASA’s Jet Propulsion Laboratory in Pasadena, California.

She and her colleagues studied glaciers in Antarctica that lose an average of 6.5 to 13 feet (2 to 4 meters) of elevation per year. They looked at different options to explain the variability in melting—surrounding sea ice, winds, salinity, air temperatures—and what correlated most was influxes of warmer ocean water.

“These big influxes of warm water come onto the continental shelf in some years and affect the rate at which ice melts,” Walker said. She and her colleagues are presenting the research at the AGU meeting.

Walker’s team has identified an area on the Antarctic Peninsula where warmer waters may have infiltrated inland, under the ice shelf—which could have impacts on sea level rise.

Float and ship measurements around Antarctica are scarce, but deep water temperature measurements can be achieved using tagged seals. That has its drawbacks, however: “It’s random, and we can’t control where they go,” Walker said. Satellite measurements of ocean heat content and temperatures would be very useful for the Southern Ocean, she added.

Ocean temperatures also impact life in the ocean—from microscopic phytoplankton on up the food chain. Different phytoplankton thrive at different temperatures and need different nutrients.

“Increased stratification in the ocean due to increased heating is going to lead to winners and losers within the phytoplankton communities,” said Stephanie Schollaert Uz, a scientist at Goddard.

In research presented this week at AGU, she took a look 50 years back. Using temperature, sea level and other physical properties of the ocean, she generated a history of phytoplankton extent in the tropical Pacific Ocean, between 1958 and 2008. Looking over those five decades, she found that phytoplankton extent varied between years and decades. Most notably, during El Niño years, water currents and temperatures prevented phytoplankton communities from reaching as far west in the Pacific as they typically do.

Digging further into the data, she found that where the El Niño was centered has an impact on phytoplankton. When the warmer waters of El Niño are centered over the Eastern Pacific, it suppresses nutrients across the basin, and therefore depresses phytoplankton growth more so than a central Pacific El Niño.

“For the first time, we have a basin-wide view of the impact on biology of interannual and decadal forcing by many El Niño events over 50 years,” Uz said.

As ocean temperatures impact processes across the Earth system, from climate to biodiversity, Tyler will continue to improve this novel magnetic remote sensing technique, to improve our future understanding of the planet.

Note: The above post is reprinted from materials provided by NASA.

Scientists redefine horned dinosaur relationships by naming two new ceratopsian tribes

Representative Image: Achelousaurus. Credit: Mariana Ruiz/Mariana Ruiz

Scientists have named two new clades, or tribes, of horned dinosaurs (ceratopsians) based on fossils collected from the United States and Alberta, Canada. The new tribes are Nasutoceratopsini and Centrosaurini. Research describing the updated relationships among horned dinosaurs appears online in the Canadian Journal of Earth Sciences.

Nasutoceratopsini includes horned dinosaurs such as Avaceratops from Montana and Nasutoceratops from Utah. These dinosaurs grew up to 6 meters (20 feet) long, weighed more than 2 tons, and had large shields extending from the back of their skulls like Triceratops. They lived about 74-76 million years ago during the Late Cretaceous Period.

Nasutoceratopsini belongs to the subfamily Centrosaurinae, which includes dinosaurs with the most elaborate head shield ornamentation ever developed, such as the spikey Styracosaurus. In contrast, nasutoceratopsins are distinguished by having large, broad frills that lacked well-developed ornamentation. Unlike their flashy contemporaries, these dinosaurs weren’t dinosaurian show-offs, choosing instead to blend into their environments.

Work recognizing the new tribe is based on a fossil skull from the Canadian Museum of Nature in Ottawa, Canada, collected almost 80 years ago in southern Alberta. Although the skull is too fragmentary to be given a new name, its distinctive unornamented shield allowed the scientists to tie it and horned dinosaur species from Utah and Montana together into a new grouping. Although all nasutoceratopsins lack shield ornamentation, they had two long brow horns above their eyes.

“Nasutoceratopsins took a different evolutionary path from their centrosaurine cousins, which typically have highly ornamented skulls” said lead author Dr. Michael Ryan, Curator of Vertebrate Paleontology at the Cleveland Museum of Natural History. “We believe that the skull ornamentation was important for attracting mates. If nasutoceratopsins lacked boney ornamentation, it’s possible that they may have used distinctive coloration patterns, social behaviors or vocalizations, like modern birds do in their courtship behaviors. But we’ll never know for sure since those latter features don’t fossilize.”

The second new tribe described by the scientists, Centrosaurini, formally acknowledges its members (such as Centrosaurus) as being a natural grouping of horned dinosaurs with highly ornamented frills and short brow horns.

The fact that the two tribes are found together over a great distance in rocks of the same age indicates that they would have overlapped in the same regions at the same time.

“It’s probably similar to how two species of rhinoceros can broadly overlap in their geographic ranges, but do not actually compete with each other for resources,” said Dr. Jordan Mallon of the Canadian Museum of Nature, a co-author on the paper. “Black rhinos will feed on woody browse, while white rhinos are primarily grass grazers. Thus, the two species tend to utilize different parts of the same environments. The assumption that centrosaurins and nasutoceratopsins may have had different feeding strategies is supported by the fact that the two tribes had different types of jaws, with the lower jaws of nasutoceratopsins being shorter and deeper.

The description of the two new horned dinosaur tribes is the latest in a series of new finds being made by Ryan and Dr. David Evans of the Royal Ontario Museum as part of their Southern Alberta Dinosaur Project, which is designed to fill in knowledge gaps about Late Cretaceous dinosaurs and study their evolution. This project focuses on the paleontology of some of oldest dinosaur-bearing rocks in Alberta and neighbouring rocks in northern Montana that are of the same age.

Reference:
Michael J. Ryan, Robert Holmes, Jordan Mallon, Mark Loewen, David C. Evans. A basal ceratopsid (Centrosaurinae: Nasutoceratopsini) from the Oldman Formation (Campanian) of Alberta, Canada. Canadian Journal of Earth Sciences, 2016; 1 DOI: 10.1139/cjes-2016-0110

Note: The above post is reprinted from materials provided by Cleveland Museum of Natural History.

Researchers map New Zealand landslides with satellites, drones, helicopters, hiking boots

A University of Michigan drone inspecting a fault rupture site in New Zealand. Credit: John Manousakis

A University of Michigan-led team of geologists and engineers is mapping surface ruptures and some of the tens of thousands of landslides triggered by last month’s magnitude-7.8 earthquake in New Zealand.

The U-M-led team includes a researcher from the University of Colorado at Boulder. Working in collaboration with scientists from New Zealand’s GNS Science and the U.S. Geological Survey, they will combine observations collected by satellites, drones, helicopters and on foot to create what is expected to be the largest inventory of earthquake-triggered landslides, according to team leader and U-M geologist Marin Clark.

The high-resolution digital topographic maps the researchers create will help response teams in New Zealand determine which landslides pose the greatest threat for future sliding and for river damming that can lead to catastrophic flooding. The project is also viewed as a training exercise for future large earthquakes anticipated in places like Southern California.

The powerful New Zealand quake struck Nov. 13 near the town of Kaikoura, on the east coast of the South Island. It killed two people, generated tsunami waves several feet high and stranded hundreds of tourists who had to be evacuated by helicopter and ship.

Current estimates are that 80,000 to 100,000 landslides were triggered by ruptures along at least nine faults. About 150 of the landslides blocked river valleys, and nine are being monitored as potential threats for catastrophic flooding due to river damming.

“If the 100,000 estimate is correct, then this would be the largest documented earthquake-related landsliding event ever, slightly larger than one that occurred in China in 2008,” said Clark, U-M associate professor of earth and environmental sciences.

“The landslide dams are especially important to recognize immediately after an event like this, while there is still time to do something about them. To avoid a potentially catastrophic breach and flooding event, spillways can be constructed to drain the water.”

Members of Clark’s team went to New Zealand late last month, hiking into the affected region with handheld GPS receivers and using helicopter-based observations and drone imagery to map fault ruptures and landslides. They worked with scientists from GNS Science and the Geotechnical Engineering Extreme Events Reconnaissance Association, a volunteer organization known as GEER.

U-M scientists who made the reconnaissance trip were Adda Athanasopoulos-Zekkos, associate professor of civil and environmental engineering, and postdoctoral researcher Timothy Stahl of the Department of Earth and Environmental Sciences, who is also an NSF Postdoctoral Fellow. Clark and team member Dimitrios Zekkos, U-M associate professor of civil and environmental engineering, will travel to New Zealand next month.

The U-M-led team uses small, quad-rotor drones fitted with ultra-high-definition cameras to capture extremely detailed video images of the landslides and surface ruptures.

“Drones have totally changed how our work is done,” said Zekkos, who also used the remotely operated aerial vehicles to map landslides in Nepal—on a team led by Clark—following last year’s magnitude-7.8 earthquake there, which killed more than 8,000 people and created nearly 25,000 landslides.

“Landslides can block roads, and helicopters are expensive to operate and are often needed for other purposes after a natural disaster,” he said. “But you can quickly send a drone into places that would otherwise be practically impossible to see—and you can get really, really close.”

On Dec. 8, Clark’s team received final approval of funding from the National Science Foundation for the year-long New Zealand study. While the amount of “rapid response funding” is modest at $46,516, the NSF award also gives the researchers access to satellite imagery and supercomputers they will use to create exquisitely detailed before-and-after digital maps.

The team’s study area spans about 25,000 square miles, a region slightly larger than the state of West Virginia. The researchers will have access to stereoscopic satellite imagery of the sparsely populated, mountainous study area gathered both before and after the Nov. 13 Kaikoura earthquake.

The razor-sharp satellite images sample the surface at a 30-centimeter spacing and can recognize objects on the ground as small as 2 meters across, roughly the size of an SUV. In some cases, 1-meter resolution is possible. The pre-quake images were collected by commercial satellite company Digital Globe following New Zealand’s 2011 Christchurch earthquake, which killed 185 people.

“What’s unique about this situation is that we’ve never had high-resolution ‘before’ imagery that covers the entire area affected by a major earthquake,” Clark said.

Digital Globe is now collecting “after” images of the region affected by last month’s Kaikoura earthquake. Clark’s team will have access to both data sets.

“It’s never been done at this scale at this resolution, so this is going to give us an unprecedented view of the details of what’s happening on the ground,” she said.

Multiple satellite observations of the same ground locations from different viewing angles were combined to create stereoscopic imagery that provides a three-dimensional view of the surface. The 3-D view, in turn, enables researchers to precisely measure the elevation of surface features—including landslides.

“The 3-D models from satellite observations are not as accurate as drone-created models, but they cover much wider areas and are precise enough to measure any vertical change of more than a few tens of centimeters, or roughly the height of a beach ball,” said team member Michael Willis, assistant professor at the University of Colorado.

The satellite imagery will be used to create before-and-after digital elevation models, or DEMs, which can be thought of as extremely detailed digital topographic maps. Techniques used to generate high-resolution DEMs from stereoscopic satellite images were developed by Willis as a member of a team creating such models for the Arctic.

Knowing the exact elevation at a given point before and after a landslide allows scientists to calculate the volume of material that moved, a value that is critical when trying to assess the threat posed now and in the future, Clark said.

“Some of these landslide locations are current threats for damming and catastrophic flooding. And all of them are now more susceptible to future landsliding in response to rains,” she said. “So by knowing exactly where these landslides are and how far they’ve traveled, as well as their volume and composition, we can make better predictions about what might happen in the coming weeks, months and years.”

Data collected on foot and using drones and helicopters will be used to validate the satellite images, a process called ground truthing.

The first DEMs based on the “before” images of the affected region could be finished this month and will be provided to landslide response teams from the U.S. Geological Survey and GNS Science. DEMs based on post-quake satellite imagery could take months to complete, depending on weather and other variables.

The New Zealand project is viewed as a training exercise for future large earthquakes, including an anticipated Southern California event along the San Andreas Fault. In that case, “before” images along the San Andreas have already been collected using plane-mounted LiDAR, a surveying method that measures distance to a target by illuminating it with laser light.

The Nov. 13 New Zealand earthquake resulted from faulting on or near the boundary between the Pacific and Australian tectonic plates. At the location of the magnitude-7.8 earthquake, the Pacific plate is moving west-southwest with respect to the Australian plate at a rate of about 40 millimeters (1.6 inches) per year.

The NSF-funded New Zealand project is a collaboration between the University of Michigan and the University of Colorado at Boulder. Clark’s team also includes a collaborator from Greece, John Manousakis.

Note: The above post is reprinted from materials provided by University of Michigan.

Alpine Fault theory takes shape

Credit: Victoria University

The Alpine Fault has been assumed to be a near vertical crack, however, research published last year by Victoria scientists suggests that the fault curves under the Earth’s crust.

A study by Emily Warren-Smith, who graduates this week with a PhD in Geophysics, has added more evidence to this theory. Her results show that the fault flattens to become horizontal a few kilometres underground and underlies a wide region of the central South Island.

“The surface expression of the Alpine Fault is remarkably clear, but there is some debate about the shape of the fault as it goes several kilometres underground. So I set out to map the fault at depth,” says Emily.

“Just by observing how fast the landscape of South Island has been worn away, it is possible to look deep inside the Earth, which is remarkable.

“I collected rock samples from 30 sites across the Southern Alps. Then, in the laboratory, I analysed the crystals in these rocks using a method called fission-track thermochronology.

“By looking at tiny damage trails, the by-products of nuclear fission within the crystals, we were able to put an age on when that rock was at a certain temperature. Because we know temperatures get hotter deep underground, we can therefore figure out how long ago it was at a certain depth in the earth and calculate how fast the rocks have been moving up to the surface over the last few million years as the overlying rocks are worn away by erosion.”

Emily says the aging pattern shows rocks close to the Alpine Fault are being moved up and eroded quickly—a few millimetres per year—whereas rocks in Central Otago are much more stable and have been at the surface for longer but are still moving sideways.

“The simple explanation for this pattern is that the fault plane is horizontal in the middle of the crust, around 25 kilometres deep beneath Central Otago, and then as you get closer to the West Coast it curves to become nearly vertical at the surface. So the rocks are essentially on a conveyor belt moving sideways and then being exhumed up.”

More research needs to be done to better assess what this finding means for earthquake risk, says Emily. “Our research has told us what the Alpine Fault is doing on very long time-scales, but we are unsure of its behaviour on the scale of hundreds and thousands of years and less. For places like Wanaka and Queenstown, instead of being a hundred or so kilometres geographically away from the Alpine Fault, they’re actually only a few kilometres above it.”

The research findings were published in the American Geophysical Union journal G³.

Note: The above post is reprinted from materials provided by Victoria University.

Mountain glaciers are showing some of the strongest responses to climate change

Hintereisferner Glacier in Austria is one of the glaciers analyzed in the study. The edge of the glacier is 2.8 km (1.75 miles) farther up the valley than it was in 1880.A. Lambrecht/World Glacier Monitoring Service

Mountain glaciers have long been a favorite poster child of climate change. The near-global retreat of glaciers of the last century provides some of the most iconic imagery for communicating the reality of human-driven climate change.

But the scientific basis for their retreat has been less clear. Glaciers respond slowly to any climate changes, they are susceptible to year-to-year variations in mountain weather, and some of the largest are still catching up after the end of the Little Ice Age. Scientists can connect climate change to the overall retreat of glaciers worldwide, but linking an individual glacier’s retreat to climate change has remained a subject of debate.

The last report from the Intergovernmental Panel on Climate Change concluded only that it was “likely” that a “substantial” part of mountain glacier retreat is due to human-induced climate change—a much weaker conclusion than for temperature and other things.

Now, using statistical techniques to analyze 37 mountain glaciers around the world, a University of Washington study finds that for most of them the observed retreat is more than 99 percent likely due to climate change. In the climate report’s wording, it is “virtually certain” that the retreat of these mountain glaciers is due to climate change over the past century.

“Because of their decades-long response times, we found that glaciers are actually among the purest signals of climate change,” said Gerard Roe, a UW professor of Earth and space sciences. He is corresponding author of the study published Dec. 12 in Nature Geoscience, and presented this week at the American Geophysical Union’s annual fall meeting in San Francisco.

The new study analyzes specific glaciers with a history of length observations, and nearby weather records of temperature and precipitation. The authors also sought different glacier locations, focusing on roughly seven glaciers in each of five geographic regions: North America, Europe, Asia, Scandinavia and the Southern Hemisphere.

“We evaluate glaciers which are hanging on at high altitudes in the deserts of Asia as well as glaciers that are being beaten up by midlatitude storms in maritime climate settings,” Roe said. “The thickness, slope and area of the glaciers are different, and all of those things affect the size of the glacier length fluctuations.”

Co-authors are Florian Herla , an undergraduate student at the University of Innsbruck in Austria, and Marcia Baker, a UW professor emeritus of atmospheric sciences and Earth and space sciences.

The authors used statistical tools to compare the natural, weather-induced variations in a glacier’s length with its observed changes over the last 130 years, and establish a signal-to-noise ratio. They then use that to calculate the probability that observed retreats would have happened without any background change in the climate.

The iconic Hintereisferner Glacier in Austria has retreated 2.8 km (1.75 miles) since 1880. Results show that climate change is extremely likely to be responsible for its retreat, with the probability that the changes are natural variations being less than 0.001 percent, or one in 100,000.

Likewise, for the well-known Franz Josef Glacier in New Zealand, even though the glacier has experienced re-advances of up to 1 kilometer (0.6 miles) in a given decade, there is a less than 1 percent chance that natural variations could explain the overall 3.2 kilometers (2 miles) retreat in the last 130 years.

The least significant retreats among the glaciers studied were for Rabots Glacier in northern Sweden, and South Cascade Glacier in Washington state, with probabilities of 11 and 6 percent, respectively, that their retreats might be natural variability.

“South Cascade is at the end of the Pacific storm track, and it experiences a high degree of wintertime variability. Average wintertime snowfall generates about 3 meters (10 feet) of ice per year, whereas for glaciers in desert Asia, ice accumulation might be as low as 10 centimeters (4 inches) per year,” Roe said. “So they’re experiencing very different climate settings. As a result, their variability, and also their sensitivity to climate change, varies from place to place.”

The method uses a signal-to-noise ratio that relies on observational records for glacier length, local weather, and the basic size and shape of the glacier, but does not require detailed computer modeling. The technique could be used on any glacier that had enough observations.

Overall, the results show that changes in the 37 glaciers’ lengths are between two and 15 standard deviations away from their statistical means. That represents some of the highest signal-to-noise ratios yet documented in natural systems’ response to climate change.

“Even though the scientific analysis arguably hasn’t always been there, it now turns out that it really is true—we can look at these glaciers all around us that we see retreating, and see definitive evidence that the climate is changing,” Roe said. “That’s why people have noticed it. These glaciers are stunningly far away from where they would have been in a preindustrial climate.”

Note: The above post is reprinted from materials provided by University of Washington.

Fish fossil hunter poles apart

Professor John Long, right, during an earlier expedition in 1992. Credit: Flinders University

It’s a white Christmas with a difference for an international gang of scientists heading from McMurdo Base to the Transantarctic Mountains in a gruelling hunt for fossils older than dinosaurs.

Among them is Flinders University Strategic Professor in Palaeontology John Long, who twice ventured to Antarctica in the late 1980s and early 1990s.

In a bid to explain the transition of vertebrate life from the water to land, Professor Long has joined a new multi-year expedition funded by the National Sciences Foundation to scour the rocky, dry, desert-like valleys between Antarctic glaciers to piece together the path of evolution.

While most of Antarctica is covered by a deep sheet of ice, the Transantarctic Mountains reach up above the ice and expose pristine sheets of sedimentary rock that are in places rich in fossils.

The team, including Professor Neil Shubin from the University of Chicago, Associate Professor Adam Maloof from Princeton University, Australian National University’s Professor Tim Senden and Ted Daeschler from Drexel University in the US, are looking for well-preserved Devonian fish fossils in this remote location.

“We are looking for Late Devonian (up to 390 million year old) fossils, including fossil sharks and lobe-finned fishes that have been recently discovered in Canada’s Arctic,” says Professor Long.

“Following on from Neil Shubin’s work on Tiktaalik, we hope to find similar fishes down in Antarctica.

“Well-preserved Devonian fish fossils shed light on the big question of how did fishes evolve into the first four-limbed land animals (tetrapods, or early amphibians).

“There are also well-preserved placoderms and very old fossil sharks, so we could find out a lot about the early radiation of the first jawed fishes.”

The Devonian Period ended approximately 120 million years before the first dinosaurs appeared. It was a time when fish were diverse and abundant and fossils from that period have provided important clues to how life adapted and made the transition from the water to land.

The 375-million-year-old Tiktaalik roseae fossil is a key transitional form between fish and land animals, published as the cover story in Nature in April 2006.

The Antarctica research will continue through to mid-January 2017 and continue in the summer of 2018-19. As well as the centres of evolutionary change, the expedition hopes to find species new to science.”

Filling in the gaps in the incompletely-known Late Devonian interval will also help to answer questions about the diversification of major groups of fishes, the origin of limbed vertebrates, along with the invasion of land by plants and animals.

Professor Long tells of sub-zero conditions and hazardous climbing conditions in his book Mountains of Madness (Joseph Henry Press, 2001) about his earlier expeditions. His other book, Frozen in Time, is the first book to give a complete overview of Antarctic palaeontology (CSIRO, 2011) .

He survived the earlier experience to become President of The Society of Vertebrate Palaeontology, author of hundreds of scientific papers and even adult and children’s books about fossils.

He has earned an international reputation for finding the world’s oldest vertebrate embryo and uncovering the origins of sex after analysing the sexual reproduction of 385 million year-old fossilised fish found in Scotland.

Along with cold-climate fossil hunts, he is a pioneer of the remote and very hot Gogo fossil site in northern Western Australia. The perfectly preserved 3-D fish fossils have yielded many significant discoveries, including mineralised soft tissues, the origins of complex sexual reproduction in vertebrates.

His discoveries include the State Fossil Emblem of WA (Mcnamaraspis), the mother fish with the world’s oldest vertebrate embryo (Materpiscis), a tetrapod-like fish with large holes on top of its head for air-breathing (Gogonasus), and the oldest evidence for copulation in vertebrates (Microbrachius). He has published seven papers in Nature and Science in the past 10 years, with four of these first authored.

Note: The above post is reprinted from materials provided by Flinders University.

Antarctic Ice Sheet study reveals 8,000-year record of climate change

Iceberg in the Weddell Sea. Credit: Mike Weber

An international team of researchers has found that the Antarctic Ice Sheet plays a major role in regional and global climate variability – a discovery that may also help explain why sea ice in the Southern Hemisphere has been increasing despite the warming of the rest of the Earth.

Results of the study, co-authored by Michael Weber, a paleoclimatologist and visiting scientist at the University of Cambridge, along with colleagues from the USA, New Zealand and Germany, are published this week in the journal Nature.

Global climate models that look at the last several thousand years have failed to account for the amount of climate variability captured in the paleoclimate record, according to lead author Pepijn Bakker, a climate modeller from the MARUM Center for Marine Environmental Studies at the University of Bremen in Germany.

The researchers first turned their attention to the Scotia Sea. “Most icebergs calving off the Antarctic Ice Sheet travel through this region because of the atmospheric and oceanic circulation,” explained Weber. “The icebergs contain gravel that drop into the sediment on the ocean floor – and analysis and dating of such deposits shows that for the last 8,000 years, there were centuries with more gravel and those with less.”

The research team’s hypothesis is that climate modellers have historically overlooked one crucial element in the overall climate system. They discovered that the centuries-long phases of enhanced and reduced Antarctic ice mass loss documented over the past 8,000 years have had a cascading effect on the entire climate system.

Using sophisticated computer modelling, the researchers traced the variability in iceberg calving (ice that breaks away from glaciers) to small changes in ocean temperatures.

“There is a natural variability in the deeper part of the ocean adjacent to the Antarctic Ice Sheet that causes small but significant changes in temperatures,” said co-author Andreas Schmittner, a climate modeller from Oregon State University. “When the ocean temperatures warm, it causes more direct melting of the ice sheet below the surface, and it increases the number of icebergs that calve off the ice sheet.”

Those two factors combine to provide an influx of fresh water into the Southern Ocean during these warm regimes, according to Peter Clark, a paleoclimatologist from Oregon State University, and co-author on the study.

“The introduction of that cold, fresh water lessens the salinity and cools the surface temperatures, at the same time, stratifying the layers of water,” he said. “The cold, fresh water freezes more easily, creating additional sea ice despite warmer temperatures that are down hundreds of meters below the surface.”

The discovery may help explain why sea ice is currently expanding in the Southern Ocean despite global warming, the researchers say.

“This response is well-known, but what is less-known is that the input of fresh water also leads to changes far away in the northern hemisphere, because it disrupts part of the global ocean circulation,” explained Nick Golledge from the University of Wellington, New Zealand, an ice-sheet modeller and study co-author. “Meltwater from the Antarctic won’t just raise global sea level, but might also amplify climate changes around the world. Some parts of the North Atlantic may end up with warmer temperatures as a consequence of part of Antarctica melting.”

Golledge used a computer model to simulate how the Antarctic Ice Sheet changed as it came out of the last ice age and into the present, warm period.

“The integration of data and models provides further evidence that the Antarctic Ice Sheet has experienced much greater natural variability in the past than previously anticipated,” added Weber. “We should therefore be concerned that it will possibly act very dynamically in the future, too, specifically when it comes to projecting future sea-level rise.”

Two years ago Weber led another study, also published in Nature, which found that the Antarctic Ice Sheet collapsed repeatedly and abruptly at the end of the Last Ice Age to 19,000 to 9,000 years ago.

Reference:
Pepijn Bakker et al, Centennial-scale Holocene climate variations amplified by Antarctic Ice Sheet discharge, Nature (2016). DOI: 10.1038/nature20582

Note: The above post is reprinted from materials provided by University of Cambridge.

Mysterious ‘crater’ on Antarctica indication of vulnerable ice sheet

Meltwater stream inside the crater on the Roi Baudouin ice shelf. Credit: Stef Lhermitte

The East Antarctic ice sheet appears to be more vulnerable than expected, due to a strong wind that brings warm air and blows away the snow. That is the conclusion reached by a team of climate researchers led by Jan Lenaerts (Utrecht University/KU Leuven) and Stef Lhermitte (TU Delft/KU Leuven), based on a combination of climate models, satellite observations and on-site measurements. Their conclusions will be published in Nature Climate Change on 12 December.

“Tens of meters of rising sea levels are locked away in Antarctica”, says Lenaerts. “And our research has shown that also East Antarctica is vulnerable to climate change.”

Current IPCC projections show large uncertainties in Antarctica’s contribution to sea level rise, because the role of ice shelf processes remains uncertain. Lenaerts explains: “Little climate change is observable in East Antarctica, because the area is so isolated from the rest of the world.” However, to the researchers’ astonishment, the ice shelves in some regions of East Antarctica are melting faster than scientists had previously assumed. These ice shelves appear to be extremely sensitive to climate change.

Hotspots

Through a unique combination of field work, satellite data and a climate model, the researchers were able to explain why some parts of the East Antarctica ice shelves are melting so rapidly. This is because the strong and persistent wind transports warm, dry air to the region, and blows away the snow. This darkens the surface, which subsequently absorbs more of the sun’s heat. The result is a local warmer microclimate with a few literal ‘hotspots’. Because the ice shelf is floating in the ocean, its melting does not immediately contribute to sea level rise. However, the ice shelves around Antarctica are extremely important for ice sheet stability, because they hold back the land ice. If the ice shelves collapse, this land ice ends up in the ocean and consequently sea level will rise.

Mysterious crater

Part of the research conducted by Lenaerts and Lhermitte focused on a mysterious crater that was spotted on the King Baudoin ice shelf. “At the time, the media reported that it was probably a meteorite impact crater”, Lenaerts says. “My response was: in that area? Then it’s definitely not a meteorite; it’s proof of strong melting.”

In January 2016, the researchers visited the crater and discovered that it was a collapsed lake, with a moulin – a hole in the ice- which allowed the water to flow into the ocean. Lhermitte: “That was a huge surprise. Moulins typically are observed on Greenland. And we definitely never see them on an ice shelf.” Moreover, the researchers discovered that there were many meltwater lakes hidden under the surface of the ice, some of which were kilometres across. Underwater video images provide a clear image of the amount of meltwater present in the area.

Vulnerable

Is this a sign of climate change? “The crater isn’t new; we found it on satellite images from 1989. The amount of melt water differs immensely from year to year, but it clearly increases during warm years”, according to Lhermitte. Last year, an influential publication showed that Antarctica’s contribution to rising sea levels depends largely on the stability of these melting ice shelves. Lenaerts: “That study indicated that West Antarctica is extremely sensitive to climate change. But our research now suggests that the much larger East Antarctica ice sheet is also very vulnerable.”

Reference:
Meltwater produced by wind–albedo interaction stored in an East Antarctic ice shelf, Nature Climate Change , DOI:10.1038/nclimate3180

Note: The above post is reprinted from materials provided by KU Leuven.

During last period of global warming, Antarctica warmed 2 to 3 times more than planet average

Blustery conditions at the West Antarctica ice sheet divide, a ridge where a 3.4-kilometer borehole was drilled to acquire ice cores. The tent protected the equipment and scientists as they measured temperatures down the borehole in 2011 and 2014. Credit: U.S. Geological Survey photos

Following Earth’s last ice age, which peaked 20,000 years ago, the Antarctic warmed between two and three times the average temperature increase worldwide, according to a new study by a team of American geophysicists.

The disparity — Antarctica warmed about 11 degrees Celsius, nearly 20 degrees Fahrenheit, between about 20,000 and 10,000 years ago, while the average temperature worldwide rose only about 4 degrees Celsius, or 7 degrees Fahrenheit — highlights the fact that the poles, both the Arctic in the north and the Antarctic in the south, amplify the effects of a changing climate, whether it gets warmer or cooler.

The calculations are in line with estimates from most climate models, proving that these models do a good job of estimating past climatic conditions and, very likely, future conditions in an era of climate change and global warming.

“The result is not a surprise, but if you look at the global climate models that have been used to analyze what the planet looked like 20,000 years ago — the same models used to predict global warming in the future — they are doing, on average, a very good job reproducing how cold it was in Antarctica,” said first author Kurt Cuffey, a glaciologist at the University of California, Berkeley, and professor of geography and of earth and planetary sciences. “That is noteworthy and a confirmation that we know how the system works.”

These models currently predict that as a result of today’s global climate change, Antarctica will warm twice as much as the rest of the planet, though it won’t reach its peak for a couple of hundred years. While the most likely climate change scenario, given business-as-usual greenhouse gas emissions, is a global average increase of 3 degrees Celsius (5 degrees Fahrenheit) by 2100, the Antarctic is predicted to warm eventually by around 6 degrees Celsius (10 degrees Fahrenheit).

The new results, which are the first good calculation of Antarctica’s ice age temperature and the amount of warming since, do rule out a couple of climate models that do not include enough feedback to accurately reproduce the amplified temperature in the polar regions, Cuffey said.

Cuffey and his colleagues, including Gary Clow of the U.S. Geological Survey in Lakewood, Colorado, published their results online last week in the early edition of the Proceedings of the National Academy of Sciences.

Deglaciation in Antarctica

The analysis is based on the fact that as the world warmed following the coldest part of the last ice age 20,000 years ago, the ice deep inside the Antarctic glaciers warmed more slowly than Earth’s surface, just as a frozen turkey put into a hot oven will still be cold inside even after the surface has reached oven temperature. By measuring the remaining difference — the 20,000-year old ice deep in the West Antarctic ice sheet is about 1 degree Celsius cooler than the surface — the scientists were able to estimate the original temperature based on how fast pure ice warms up.

Clow measured twice, once in 2011 and again in 2014, the temperature in a 3.4-kilometer-deep (2-mile-deep) borehole from which the West Antarctic Sheet Divide ice core had been drilled during an eight-year project that ended in 2011. Ice at the bottom of the borehole was deposited about 70,000 years ago; ice about one-sixth of the way up about 50,000 years ago; and ice about one-third of the way to the surface 20,000 years ago.

Cuffey developed a technique to combine these temperature measurements, which are smoothed as a result of heat diffusion in the ice, with isotopic measurements of old ice to come up with an estimated temperature of 11.3 degrees, plus or minus 1.8 degrees Celsius, warming since the depths of the ice age.

Interestingly, the Antarctic temperature increased much more rapidly than did Arctic temperatures after the glacial maximum. By 15,000 years ago, Antarctica had warmed to about 75 percent of its temperature today. The Arctic took another 3,000-4,000 years to warm this much, primarily because of the fact that the Northern Hemisphere had huge ice sheets to buffer warming, and the fact that changes in ocean currents and Earth’s orbital configuration accelerated warming in the south.

Antarctica was also more sensitive to global carbon dioxide levels, Cuffey said, which increased as the global temperature increased because of changing ocean currents that caused upwelling of carbon-dioxide-rich waters from the depths of the ocean.

The situation today, with global warming driven primarily by human emissions of carbon dioxide from burning fossil fuels, is different from natural cycles, he said. The ability of the oceans to take up carbon dioxide cannot keep up with the rising levels of greenhouse gases in the atmosphere, which means carbon dioxide and global temperatures will continue to increase unless humans cut their carbon dioxide emissions.

Reference:
Kurt M. Cuffey, Gary D. Clow, Eric J. Steig, Christo Buizert, T. J. Fudge, Michelle Koutnik, Edwin D. Waddington, Richard B. Alley, Jeffrey P. Severinghaus. Deglacial temperature history of West Antarctica. Proceedings of the National Academy of Sciences, 2016; 201609132 DOI: 10.1073/pnas.1609132113

Note: The above post is reprinted from materials provided by University of California – Berkeley.

New study finds mammals during age of dinosaurs packed a powerful bite

A rendering of the early marsupial relative, Didelphodon vorax. This opossum-sized mammal had pound-for-pound, the strongest bite force of any mammal ever recorded and could eat a wide variety of foods, including snails and small dinosaurs. Credit: Misaki Ouchida

Move over, hyenas and saber-toothed cats; there’s a mammal with an even stronger bite. A new study by Burke Museum and University of Washington paleontologists describes an early marsupial relative called Didelphodon vorax that lived alongside ferocious dinosaurs and had, pound-for-pound, the strongest bite force of any mammal ever recorded.

Published in the journal Nature Communications, the team’s findings suggest mammals were more varied during the Age of Dinosaurs than previously believed. Didelphodon was able to eat a variety of foods, and was likely a scavenger-predator who could eat prey ranging from snails to small dinosaurs.

In addition, the team re-traced the origins of marsupials. Previous theories attribute South America as the origin of marsupials, but anatomical features of the Didelphodon point to marsupials originating in North America 10-20 million years earlier than originally thought, and later dispersing and diversifying in South America.

“What I love about Didelphodon vorax is that it crushes the classic mold of Mesozoic mammals,” Dr. Gregory P. Wilson, Burke Museum Adjunct Curator of Vertebrate Paleontology and University of Washington Associate Professor of Biology, said. “Instead of a shrew-like mammal meekly scurrying into the shadows of dinosaurs, this badger-sized mammal would’ve been a fearsome predator on the Late Cretaceous landscape–even for some dinosaurs.”

All of these findings are made possible by four fossil specimens recently discovered in the 69-66 million-year-old deposits of the Hell Creek Formation in Montana and North Dakota. Prior to these discoveries, the 60 known species of metatherians (marsupials and their closest relatives) from the Cretaceous of North America — including Didelphodon — were almost all identified through fragments of jaw bones or teeth, providing a limited glimpse into marsupials’ closest relatives. These four fossils include a nearly-complete skull from the North Dakota Geological Survey State Fossil collection, a partial snout and an upper jaw bone from the Burke Museum’s collections, and another upper jaw from the Sierra College Natural History Museum.

By analyzing never-before-seen parts of Didelphodon’s anatomy, Dr. Wilson and his colleagues were able to determine these marsupial relatives were about the size of today’s Virginia opossum and were the largest metatherian from the Cretaceous. With a nearly complete skull to measure, they were able to estimate the overall size of Didelphodon, which ranged from 5.3-11.5 pounds. To test the bite force of Didelphodon, Abby Vander Linden, a UW Biology research technician in Burke Museum Curator of Mammalogy Dr. Sharlene Santana’s lab and now a graduate student at University of Massachusetts Amherst, CT-scanned the fossils and compared the gaps in reconstructed skulls where jaw muscles would go to present-day mammals with known bite forces. Bite force measurements indicate that pound-for-pound, Didelphodon had the strongest bite force of any mammal that has ever lived. In addition to the bite force, Didelphodon’s canines were similar to living felines and hyenas — suggesting they could handle biting into bone, biting deep and killing prey. Its shearing molars and big rounded premolars, combined with powerful jaws and jaw muscles indicate it had a specific niche in the food web as a predator or scavenger capable of crushing hard bone or shells, and was capable of eating prey as big as it was–even possibly small dinosaurs.

“I expected Didelphodon to have a fairly powerful bite based on the robust skull and teeth, but even I was surprised when we performed the calculations and found that, when adjusted for body size, it was capable of a stronger pound-for-pound bite than a hyena,” Vander Linden said. “That’s a seriously tough mammal.”

Co-author Dr. Jonathan Calede, former UW Biology graduate student and now a visiting assistant professor at Bucknell University, also examined “microwear” patterns, or tiny pits and scratches on the specimens’ teeth, to indicate what the animals were eating as their “last suppers” (most likely one-to-two days before the animals died). By comparing the microwear patterns from Didelphodon to the teeth of other fossilized species and current-day mammals with known diets from the Burke’s mammal collection, Calede found Didelphodon was an omnivore that likely consumed a range of vertebrates, plants and hard-shelled invertebrates like molluscs and crayfish, but few insects, spiders and annelids (earthworms and leeches).

“The interesting thing about these fossils is that they allowed us to study the ecology of Didelphodon from many angles,” Calede said. “The strength of the conclusions come from the convergence of microwear with bite force analysis, studies of the shape and breakage of the teeth, as well as the shape of the skull as a whole.”

In addition to learning much more about the biology of Didelphodon, the newly-described skull features on these fossils provide clues that help clarify the origin of all marsupials. The team found five major lineages of marsupial ancestors and marsupials themselves diverged in North America 100-85 million years ago. Marsupial relatives also got larger and ate a wider variety of foods, coinciding with an increase in diversity of other early mammals and flowering plants. Most of this North American diversity was then lost gradually from the late Campanian to Maastrichtian (79-66 million-years-ago) and then abruptly during the Cretaceous-Palaeogene (66 million-years-ago) mass extinction that also killed all dinosaurs except birds. Around this time, marsupials’ diversity and evolution shifted to South America.

“Our study highlights how, despite decades of paleontology research, new fossil discoveries and new ways of analyzing those fossils can still fundamentally impact how we view something as central to us as the evolution of our own clade, mammals,” Dr. Wilson said.

Reference:
Gregory P. Wilson, Eric G. Ekdale, John W. Hoganson, Jonathan J. Calede & Abby Vander Linden. A large carnivorous mammal from the Late Cretaceous and the North American origin of marsupials. DOI:10.1038/ncomms13734

Note: The above post is reprinted from materials provided by University of Washington.

Rock layers preserve record of ancient sea tides near Blythe, California

Credit: University of Oregon

Five million years ago, the Colorado River met the Gulf of California near the present-day desert town of Blythe, California. The evidence, say University of Oregon geologists, is in the sedimentary rocks exposed at the edges of the valley where the river flows today.

The layers vary rhythmically in thickness, reflecting the influx of sea current during strong spring and weak neap tides, and point to 330 meters (1,082 feet) of uplift of the seafloor in roughly the past 5 million years, said UO graduate student Brennan O’Connell, lead author on a paper online ahead of print in the journal Geology.

The findings provide compelling evidence that this region — the southern Bouse Formation that is rich in tidal features — once was under a northern-reaching, marine water arm of the Gulf of California. That view counters the notion that the southern Colorado River corridor was the southern-most lake of a long chain of large freshwater lakes that filled during first arrival of river waters.

“The recognition of tidal deposits in the Bouse Formation places an important new constraint on uplift of a broad region from the San Andreas fault to the western Colorado Plateau over the past 5 million years,” said co-author Rebecca J. Dorsey, a professor in the UO Department of Earth Sciences who has studied the river’s route for many years. “This study makes an important step toward resolving a 20-year-old debate about the depositional environments and tectonic significance of this area.”

The Colorado River today takes a meandering journey of some 160 miles from Blythe, passing under Interstate 10 and flowing mostly southward to where it empties into the present-day northern reach of the Gulf of California.

The lake perspective on these deposits is based on geochemical findings, including strontium, carbon and oxygen isotopes. Scientists supporting the lake theory have suggested that marine fossils found in the rocks resulted from birds carrying sea organisms into the region. The new findings, O’Connell said, complement evidence by paleontologists who have argued for a marine environment for more than 50 years based on the presence of marine fossils.

“We came at it from a new perspective,” O’Connell said. “We focused more on the features of the rocks, connecting them with both chemistry and paleontology. We wanted to understand the ancient environments these rocks were formed in by identifying distinct features. Sedimentary deposits look very different if they are produced in a lake versus a tidal setting.”

Thickness variations of the layers contain clues to depositional processes, she said. Stronger tides transport higher loads of sediment. O’Connell’s UO team used a mathematically driven Fourier analysis to graph the thickness of sedimentary layers in relation to tidal velocities. The results point to regular tidal cycles rather than random movements of sediment that would be produced by tributary river floods, storms, wind-generated lake currents or annual biochemically induced deposition.

“The stronger and higher the tides, the more sediment is transported, producing a thicker layer ” she said. “Spring tides produce thick layers of sediment, and neap tides produce thin layers. Differences in tidal current velocities are clearly seen in these layers of exposed sedimentary rocks. This didn’t happen in a lake. Lakes don’t have tides large enough to create such variations.”

Reference:
O’Connell O’Connell, Rebecca J. Dorsey, Eugene D. Humphreys. Tidal rhythmites in the southern Bouse Formation as evidence for post-Miocene uplift of the lower Colorado River corridor. Geology, 2016; G38608.1 DOI: 10.1130/G38608.1

Note: The above post is reprinted from materials provided by University of Oregon.

Amber specimen offers rare glimpse of feathered dinosaur tail

Silhouette of tail bones, soft tissues, and feather attachment points.
Credit: Ryan McKellar/Royal Saskatchewan Museum

Researchers from China, Canada, and the University of Bristol have discovered a dinosaur tail complete with its feathers trapped in a piece of amber.

The finding reported today in Current Biology helps to fill in details of the dinosaurs’ feather structure and evolution, which can’t be surmised from fossil evidence.

While the feathers aren’t the first to be found in amber, earlier specimens have been difficult to definitively link to their source animal, the researchers say.

Ryan McKellar, from the Royal Saskatchewan Museum in Canada, said: “The new material preserves a tail consisting of eight vertebrae from a juvenile; these are surrounded by feathers that are preserved in 3D and with microscopic detail.

“We can be sure of the source because the vertebrae are not fused into a rod or pygostyle as in modern birds and their closest relatives. Instead, the tail is long and flexible, with keels of feathers running down each side. In other words, the feathers definitely are those of a dinosaur not a prehistoric bird.”

The study’s first author Lida Xing from the China University of Geosciences in Beijing discovered the remarkable specimen at an amber market in Myitkyina, Myanmar in 2015.

The amber piece was originally seen as some kind of plant inclusion and destined to become a curiosity or piece of jewellery, but Xing recognized its potential scientific importance and suggested the Dexu Institute of Palaeontology buy the specimen.

The researchers say the specimen represents the feathered tail of a theropod preserved in mid-Cretaceous amber about 99 million years ago. While it was initially difficult to make out details of the amber inclusion, Xing and his colleagues relied on CT scanning and microscopic observations to get a closer look.

The feathers suggest the tail had a chestnut-brown upper surface and a pale or white underside. The specimen also offers insight into feather evolution. The feathers lack a well-developed central shaft or rachis. Their structure suggests that the two finest tiers of branching in modern feathers, known as barbs and barbules, arose before a rachis formed.

Professor Mike Benton from the School of Earth Sciences at the University of Bristol, added: “It’s amazing to see all the details of a dinosaur tail — the bones, flesh, skin, and feathers — and to imagine how this little fellow got his tail caught in the resin, and then presumably died because he could not wrestle free.

“There’s no thought that dinosaurs could shed their tails, as some lizards do today.”

The researchers also examined the chemistry of the tail inclusion where it was exposed at the surface of the amber. The analysis shows that the soft tissue layer around the bones retained traces of ferrous iron, a relic left over from haemoglobin that was also trapped in the sample.

The findings show the value of amber as a supplement to the fossil record. Ryan McKellar added: “Amber pieces preserve tiny snapshots of ancient ecosystems, but they record microscopic details, three-dimensional arrangements, and labile tissues that are difficult to study in other settings.

“This is a new source of information that is worth researching with intensity, and protecting as a fossil resource.”

The researchers say they are now “eager to see how additional finds from this region will reshape our understanding of plumage and soft tissues in dinosaurs and other vertebrates.”

Reference:
Lida Xing, Ryan C. McKellar, Xing Xu, Gang Li, Ming Bai, W. Scott Persons IV, Tetsuto Miyashita, Michael J. Benton, Jianping Zhang, Alexander P. Wolfe, Qiru Yi, Kuowei Tseng, Hao Ran, Philip J. Currie. A Feathered Dinosaur Tail with Primitive Plumage Trapped in Mid-Cretaceous Amber. Current Biology, 2016; DOI: 10.1016/j.cub.2016.10.008

Note: The above post is reprinted from materials provided by University of Bristol.

Fossilized evidence of a tumor in a 255-million-year-old mammal forerunner

Sketch of a gorgonopsian head, in side view. Credit: CCA 3.0/Dmitry Dogdanov

When paleontologists at the University of Washington cut into the fossilized jaw of a distant mammal relative, they got more than they bargained for — more teeth, to be specific.

As they report in a letter published Dec. 8 in the Journal of the American Medical Association Oncology, the team discovered evidence that the extinct species harbored a benign tumor made up of miniature, tooth-like structures. Known as a compound odontoma, this type of tumor is common to mammals today. But this animal lived 255 million years ago, before mammals even existed.

“We think this is by far the oldest known instance of a compound odontoma,” said senior author Christian Sidor, a UW professor of biology and curator of vertebrate paleontology at the Burke Museum of Natural History and Culture. “It would indicate that this is an ancient type of tumor.”

Before this discovery, the earliest known evidence of odontomas came from Ice Age-era fossils.

“Until now, the earliest known occurrence of this tumor was about one million years ago, in fossil mammals,” said Judy Skog, program director in the National Science Foundation’s Division of Earth Sciences, which funded the research. “These researchers have found an example in the ancestors of mammals that lived 255 million years ago. The discovery suggests that the suspected cause of an odontoma isn’t tied solely to traits in modern species, as had been thought.”

In humans and other mammals, a compound odontoma is a mass of small “toothlets” amalgamated together along with tooth tissues like dentin and enamel. They grow within the gums or other soft tissues of the jaw and can cause pain and swelling, as well as disrupt the position of teeth and other tissues. Since odontomas do not metastasize and spread throughout the body, they are considered benign tumors. But given the disruptions they cause, surgeons often opt to remove them.

Surgery was not an option for the creature studied by Sidor’s team. It was a gorgonopsian, a distant mammal relative and the apex predator during its pre-dinosaur era about 255 million years ago. Gorgonopsians are part of a larger group of animals called synapsids, which includes modern mammals as its only living member. Synapsids are sometimes called “mammal-like reptiles” because extinct synapsids possess some, but not all, of the features of mammals. The first mammals evolved over 100 million years ago.

“Most synapsids are extinct, and we — that is, mammals — are their only living descendants,” said Megan Whitney, lead author and UW biology graduate student. “To understand when and how our mammalian features evolved, we have to study fossils of synapsids like the gorgonopsians.”

Paleontologists have categorized many “mammal-like” features of gorgonopsians. For example, like us, they have teeth differentiated for specialized purposes. But Whitney started studying gorgonopsian teeth to see if they had another mammalian feature.

“Most reptiles alive today fuse their teeth directly to the jawbone,” said Whitney. “But mammals do not: We use tough, but flexible, string-like tissues to hold teeth in their sockets. And I wanted to know if the same was true for gorgonopsians.”

A purely external examination of gorgonopsian fossils wouldn’t answer this question. Whitney had to take the risky and controversial approach of slicing into a fossilized gorgonopsian jaw: looking at thin sections of jaw and tooth under a microscope to see how the tooth was nestled within its socket. Since this technique would damage the fossil, Whitney and Larry Mose, a UW undergraduate student working with her, used a solitary or “orphan” gorgonopsian lower jaw that Sidor had collected in southern Tanzania.

Mose prepared multiple thin slices from the gorgonopsian jaw — each only about as thick as a sheet of notebook paper — and mounted them onto slides. He and Whitney immediately noticed something unexpected within the jaw: embedded next to the root of the canine were irregular clusters of up to eight tiny, round objects.

At higher magnification under a microscope, Whitney discovered that the objects within each cluster resembled small, poorly differentiated teeth, or toothlets. The toothlets even harbored distinct layers of dentin and enamel.

“At first we didn’t know what to make of it,” said Whitney. “But after some investigation we realized this gorgonopsian had what looks like a textbook compound odontoma.”

At 255 million years, this is by far the oldest reported evidence for an odontoma — and possibly the first case in a non-mammal. According to Sidor, odontomas have been reported in archaeological specimens, as well as fossilized mammoths and deer. But those cases all date to within the last million years or so. Since this synapsid had an odontoma, it would indicate that this mammalian condition existed well before the first mammals had evolved.

“This discovery demonstrates how the fossil record can tell us a lot about our present-day lives — even the diseases or pathologies that are part of our mammalian heritage,” said Sidor. “And you could never tell that this creature had it from the outside.”

Reference:
Christian A. Sidor, PhD et al. Odontoma in a 255-Million-Year-Old Mammalian Forebear. Journal of the American Medical Association Oncology, December 2016 DOI: 10.1001/jamaoncol.2016.5417

Note: The above post is reprinted from materials provided by University of Washington.

Will Earth still exist 5 billion years from now?

This is a schematic view of the candidate planet’s orbit in L2 Puppis disk.
Credit: P. Kervella (CNRS / U. de Chile / Observatoire de Paris / LESIA)

What will happen to Earth when, in a few billion years’ time, the Sun is a hundred times bigger than it is today? Using the most powerful radio telescope in the world, an international team of astronomers has set out to look for answers in the star L2 Puppis. Five billion years ago, this star was very similar to the Sun as it is today.

“Five billion years from now, the Sun will have grown into a red giant star, more than a hundred times larger than its current size,” says Professor Leen Decin from the KU Leuven Institute of Astronomy. “It will also experience an intense mass loss through a very strong stellar wind. The end product of its evolution, 7 billion years from now, will be a tiny white dwarf star. This will be about the size of the Earth, but much heavier: one tea spoon of white dwarf material weighs about 5 tons.”

This metamorphosis will have a dramatic impact on the planets of our Solar System. Mercury and Venus, for instance, will be engulfed in the giant star and destroyed.

“But the fate of the Earth is still uncertain,” continues Decin. “We already know that our Sun will be bigger and brighter, so that it will probably destroy any form of life on our planet. But will the Earth’s rocky core survive the red giant phase and continue orbiting the white dwarf?”

To answer this question, an international team of astronomers observed the evolved star L2 Puppis. This star is 208 light years away from Earth — which, in astronomy terms, means nearby. The researchers used the ALMA radio telescope, which consists of 66 individual radio antennas that together form a giant virtual telescope with a 16-kilometre diameter.

“We discovered that L2 Puppis is about 10 billion years old,” says Ward Homan from the KU Leuven Institute of Astronomy. “Five billion years ago, the star was an almost perfect twin of our Sun as it is today, with the same mass. One third of this mass was lost during the evolution of the star. The same will happen with our Sun in the very distant future.”

300 million kilometres from L2 Puppis — or twice the distance between the Sun and the Earth — the researchers detected an object orbiting the giant star. In all likelihood, this is a planet that offers a unique preview of our Earth five billion years from now.

A deeper understanding of the interactions between L2 Puppis and its planet will yield valuable information on the final evolution of the Sun and its impact on the planets in our Solar System. Whether the Earth will eventually survive the Sun or be destroyed is still uncertain. L2 Puppis may be the key to answering this question.

Reference:
P. Kervella, W. Homan, A. M. S. Richards, L. Decin, I. McDonald, M. Montargès, K. Ohnaka. ALMA observations of the nearby AGB star L2 Puppis. Astronomy & Astrophysics, 2016; 596: A92 DOI: 10.1051/0004-6361/201629877

Note: The above post is reprinted from materials provided by KU Leuven.

Longest-living animal gives up ocean climate secrets

Credit: Paul Butler

A study of the longest-living animal on Earth, the quahog clam, has provided researchers with an unprecedented insight into the history of the oceans.

By studying the chemistry of growth rings in the shells of the quahog clam, an international team led by experts from Cardiff University and Bangor University have pieced together the history of the North Atlantic Ocean over the past 1000 years and discovered how its role in driving the atmospheric climate has drastically changed.

The research team showed that prior to the industrial period (pre AD 1800), changes in the North Atlantic Ocean, brought about by variations in the Sun’s activity and volcanic eruptions, were driving our climate and led to changes in the atmosphere, which subsequently impacted our weather.

However, this has switched during the industrial period (1800-2000) and changes in the North Atlantic are now synchronous with, or lag behind, changes in the atmosphere, which the researchers believe could be due to the influences of greenhouse gases.

The results are extremely important in terms of discerning how changes in the North Atlantic Ocean may impact the climate and the weather across the Northern Hemisphere in the future.

The findings have been published in the journal Nature Communications.

The quahog clam, also known as a hard clam or chowder clam, is an edible mollusc native to the continental shelf seas of North America and Europe that can live for over 500 years.

The chemistry in the growth rings in the shells of the clam — which occur much like the annual growth rings in the centre of trees — can act as a proxy for the chemical make-up of the oceans, enabling researchers to reconstruct a history of how the oceans have changed over the past 1000 years with unprecedented dating precision.

By comparing this record with records of solar variability, volcanic eruptions and atmospheric air temperatures, the researchers have been able to construct a bigger picture and investigate how each of these things have been linked to one another over time.

Lead author of the study Dr David Reynolds, from the School of Earth and Ocean Sciences, said: “Our results show that solar variability and volcanic eruptions play a significant role in driving variability in the oceans over the past 1000 years. Results also showed that marine variability has played an active role in driving changes to Northern Hemisphere air temperatures in the pre-industrial era.

“This trend is not seen during the industrial period, where Northern Hemisphere temperature changes, driven by humanmade forcings, precede variability in the marine environment.”

Up until now, instrumental observations of the oceans have only spanned the last 100 years or so, whilst reconstructions using marine sediment cores come with significant age uncertainties. This has limited the ability of researchers to look further back in time and examine the role the ocean plays in the wider climate system using such detailed statistical analyses.

Co-author of the study Professor Ian Hall, from the School of Earth and Ocean Sciences, said: “Our results highlight the challenge of basing our understanding of the climate system on generally short observational records.

“Whilst they likely capture an element of natural variability, the strong anthropogenic trends observed over recent decades likely masks the true natural rhythms of the climate system. These data therefore provides an invaluable archive of the natural state of the ocean system and the expression of anthropogenic change over the last 1000 years.

“If we are to continue to develop the most robust near-term predictions of future climate change we must continue to develop robust reconstructions of past ocean variability.”

Reference:
D. J. Reynolds, J. D. Scourse, P. R. Halloran, A. J. Nederbragt, A. D. Wanamaker, P. G. Butler, C. A. Richardson, J. Heinemeier, J. Eiríksson, K. L. Knudsen, I. R. Hall. Annually resolved North Atlantic marine climate over the last millennium. Nature Communications, 2016; 7: 13502 DOI: 10.1038/ncomms13502

Note: The above post is reprinted from materials provided by Cardiff University.

Island volcano monitoring system tested at Nishinoshima

Illustration of the completed Vector Tsunameter real time observation system. Credit: Kobe University

During the October cruise of KS16-16 a research team with members from the Kobe University Graduate School of Science, the University of Tokyo Earthquake Research Institute and the Japan Agency for Marine-Earth Science and Technology (JAMSTEC) tested a newly-developed island volcano monitoring system in the seas around Nishinoshima, where eruptions have been continuing since November 2013.

The monitoring system uses a wave glider that can operate autonomously relying solely on wave power. The glider is equipped with cameras for visual observation of the volcano, a GPS wave gauge that can detect tsunami caused by volcanic collapse, and a gauge that checks for earthquakes and air vibrations by measuring sonic waves in the air and water. During the system’s test run around the island researchers were able to confirm that these features were functioning correctly.

In order to monitor in real time, they continuously transmitted data from the wave gauge and earthquake/air tremor gauge to a server on the mainland 1000km from Nishinoshima using satellite transmissions.

Based on this test run, the development stages of the island volcano monitoring system are almost complete, and the group plans to start preparing the system for practical use in monitoring Japan’s numerous island volcanoes.

Note: The above post is reprinted from materials provided by Kobe University.

Seismically active Katmandu region in store for larger earthquake

Professor Steve Wesnousky of the College of Science at the University of Nevada, Reno examines layers of rock and soil in a trench in Tribeni, a small town in central Nepal, to study the frequency of large earthquakes on the Himalayan Frontal Fault. In a recently published study, his team concludes this 200-kilometer long section of the earthquake fault could rupture spontaneously in a magnitude 8 or greater earthquake causing more deaths and damage than the 2015 Gorkha earthquake.
Credit: University of Nevada, Reno.

An earthquake much more powerful and damaging than last year’s 7.8 magnitude quake could rock Katmandu and the Himalayan Frontal Fault, an international team of seismic experts has concluded. The unsettling news comes after field research and analysis in the year following the 2015 Gorkha earthquake, which killed 9,000 people and destroyed 600,000 structures throughout the region.

Geophysics professor and director of the Center for Neotectonic Studies, Steve Wesnousky of the University of Nevada, Reno, has been studying the Himalayan Frontal Fault for 20 years. He was one of the first scientists into the region to assess the geophysical impacts following last year’s quake. His latest research was published in the Elsevier science journal Earth and Planetary Science Letters.

“We conducted a number of paleoearthquake studies in the vicinity of Katmandu in the past year, digging trenches and studying soils and faultlines looking back over the past 2,000 years,” Wesnousky said. “Coupled with the historical record, it’s apparent the faults are capable of earthquakes far greater than the Gorkha earthquake.”

Last year’s earthquake and aftershocks could be viewed as a warning of a more powerful earthquake that could rock the region with even more devastating effects. The team’s observations shows the Tribeni site is probably approaching or is in the later stages of strain accumulation before a large earthquake, which could produce 15- to 30-foot high fractures in the earth.

“The sum of our observations suggest that this section of the Himalayan Frontal Thrust fault, extending about 200 kilometers from Tribeni to Bagmati, may rupture simultaneously, and the next great earthquake near Kathmandu may rupture an area significantly greater than in the Gorkha earthquake,” Wesnousky said. “It is prudent to consider that the fault near Kathmandu is in the later stages of a strain accumulation cycle prior to a great thrust earthquake, much greater than occurred in 2015. In these regards, the 2015 Gorkha earthquake did not diminish the current level of seismic hazard in Kathmandu.”

Funded by the National Science Foundation, the team visited the Katmandu region several times for hands-on study of the faultlines. They dug two deep trenches near the mouths of major rivers at Tribeni and Bagmati. They examined structural, stratigraphic (layers of rocks and soils) and radiocarbon relationships in trenches across the fault where it has produced steep banks in soil deposited by the rivers.

In these trenches is evidence that earthquake displacement along this part of the Himalayan Frontal Thrust has produced surface ruptures resulting in a scarp, a steep bank, of at least five meters or 15 feet vertical separation sometime between the years 1221 and 1262 in Tribeni, located about 200 kilometers south of Kathmandu. At the Bagmati site, the vertical separation across the scarp registers about 10 meters, or 30 feet and possibly greater, and was formed between 1031 and 1321 AD.

“The scenario we developed hypothesizes that the next great earthquake may begin to the west near Tribeni and propagate into the section of fault beneath Kathmandu that did not rupture during the 2015 Gorkha earthquake,” Wesnousky said. “The length of such a rupture would be about 200 kilometers or greater and capable of producing a magnitude 8 or greater earthquake. This scenario is not unique.”

Wesnousky’s research team includes Deepak Chamlagain, a professor at Tribhuvan University in Kathmandu, Yashurhiro Kumahara a professor at Hiroshima University in Japan, Ian Pierce of the Center for Neotectonics Studies and the Nevada Seismological Laboratory at the University of Nevada, Reno, Alina Karki of Tribhuvan University and Dipendra Gautam of the Centre for Disaster and Climate Change Studies in Kathmandu.

Wesnousky, a member of the Nevada Seismological Laboratory in the College of Science, has six peer-reviewed scientific papers about the Himalayan fault and more than 100 papers about earthquakes published during his career. His work centers on the foothills south of Kathmandu, just over the border in India and he has expanded his study area following the historic quake, the first large quake in that area since 1930.

Following the April 2015 quake he and two of his doctoral students, Ian Pierce and Steve Angster, spent six days in the area south of Kathmandu looking for ground ruptures, following leads from villagers and residents as well as visiting various other sites studied in the past.

During their studies, the graduate students sent photos and updates about their work in the Himalayas, which are posted on the University’s website at http://www.unr.edu/science/himalayan-quake-research

Their observations are working to further define the seismic hazard of the region as well as the mechanics of fault rupture along major continental thrust faults.

A Fulbright Scholar, Wesnousky has studied earthquakes, faultlines and seismic activity throughout Nevada and parts of South America, California, Pakistan, New Zealand, Mexico, Japan, the Solomon Islands, China and India.

“Steve embodies the quintessential University professor and scientist, conducting a full body of relevant research, successful teaching and community outreach,” Jeff Thompson, dean of the College of Science, said. “He has done a wonderful job with the neotectonics center, informing the body of knowledge on the world’s most hazardous earthquake fault zones.”

 

Note: The above post is reprinted from materials provided by University of Nevada, Reno.

Fish fossils reveal how tails evolved, professor finds

Aetheretmon (facing right) display the ancestral state of two tails, a fleshy one on top of a fin. Teleosts (middle) and tetrapods have each lost one. Credit: John Megahan

Despite their obvious physical differences, elephants, lizards and trout all have something in common. They possess elongated, flexible structures at the rear of their bodies that we call tails. But a new study by a University of Pennsylvania paleobiologist reveals that the tails of fish and the tails of tetrapods, or four-limbed animals, are in fact entirely different structures, with different evolutionary histories.

With an analysis of 350-million-year-old fossil fish hatchlings, Lauren Sallan, an assistant professor in the School of Arts & Science’s Department of Earth and Environmental Science, showed that these ancient juvenile fish had both a scaly, fleshy tail and a flexible fin, one sitting atop the other. A similar dual tail structure is seen in the embryos of modern teleosts, a group of ray-finned fish that make up more than 95 percent of living fish species.

Over evolutionary time, to adapt to their environments, adult teleosts and tetrapods each lost one of these tails.

“The tetrapod tail likely started as a limb-like outgrowth in the first vertebrates, while the fish caudal fin started as a co-opted median fin, like the dorsal fin,” Sallan said. “All vertebrate tail diversity might be explained by the relative growth and loss of these two tails, with the remaining fleshy tail stunted in humans as in fishes.”

Sallan reported her findings in the journal Current Biology.

For nearly 200 years, scientists from Darwin contemporary Thomas Henry Huxley to Stephen Jay Gould pointed to the larval stage of modern teleost fish, which have an asymmetrial tail that resembles those of ancient adult ray-finned fish, as a prime example of recapitulation theory, the idea that the growth and development of organisms takes them through stages that mirror the evolutionary steps from simple to more complex organisms.

This example, however, had a notable weakness: a lack of fossils of juvenile fish ancestors. The linchpin for Sallan’s study came in the form of a series of 350-million- year-old fossil specimens of Aetheretmon valentiacum, a fish species related to teleosts. The fossils were recovered from Scotland over decades and stored in museums, but most had never been examined in detail. Unstudied specimens included the smallest known examples of the species — only 3 centimeters long — representing the earliest known stage of development for such fishes. These fossils allowed the first direct comparison between the growth stages of ancient fish and their modern teleost descendants.

Adult Aetheretmon fish possessed an asymmetrical tail, longer on the top than the bottom, which contains vertebrae. A group of modern fish called chondrosteans, which includes species such as sturgeon and paddlefish, are sometime referred to as “living fossils” and have a similar tail structure. Adult teleost tails, on the other hand, are nearly symmetrical and comprised entirely of fin.

According to recapitulation theory, juvenile Aetheretmon would have appeared to be smaller versions of the adults, exhibiting what is called direct development. Sallan’s observations found that this was not the case. The juvenile Aetheretmon in fact closely resembled modern teleost juveniles; both have a small fleshy tail containing vertebrae, similar to a lizard’s tail, overlaying a fin. As they matured, the upper tail of Aetheretmon continued to extend. In contrast, the upper portion of the tail of modern teleosts’ is stunted early and so ends up embedded in the growing body, their caudal fin instead becoming their only “tail.”

Sallan examined the tail forms of a variety of different species of fish, living and extinct, at different developmental stages, and found the same two-part structure, differently arranged, in each.

“What this shows is that ancient fish and modern fish had the same developmental starting point that has been shared over 350 million years,” said Sallan. “It’s not the ancestral tail showing up in modern teleost larvae; it’s that all fish have two different structures to their tail that have been adjusted over time based on function and ecology for all of these species.”

The analysis allows for new insights to be drawn not only about fish evolution but the evolution of vertebrates in general, as the bony, fish-like ancestors of Aetheretmon, living fishes and land-dwelling tetrapods likely had both types of tail. The vertebrae-containing tail present in Aethretmon likely represents the first limb-like growth that became the true tails in animals like lizards.

Sallan said it’s likely that the two outgrowths are governed by two different groups of genes and thus could have been subject to natural selection independently, generating large numbers of innovative forms throughout evolution.

“It tells us why we have all this diversity in fins and limbs in past and present,” Sallan said. “There might have been some lineages that favored one form over another for functional or ecological reasons. If a fish couldn’t adapt this trait, which is so vital for swimming, they might have gone extinct.”

Sallan is excited by the possibility that these findings could be evaluated by a developmental biologist to confirm the molecular pathways that generate limb outgrowth or fin placement.

“This would be an easy way of testing evolution in the lab,” she said.

 

Reference:
Lauren Sallan. Fish ‘tails’ result from outgrowth and reduction of two separate ancestral tails. Current Biology, 2016; 26 (23): R1224 DOI: 10.1016/j.cub.2016.10.036

Note: The above post is reprinted from materials provided by University of Pennsylvania.

Geoscientists size-up early dinosaurs, find surprising variation

A Coelophysis flock. Credit: Matt Celeskey

Look out your window, and you may see people of all ages and sizes roaming the street: a 6-foot-5-inch man walking beside a 4-foot-6-inch boy, for example, or a sprouting teen-ager who is much taller than a full-grown adult.

Virginia Tech geoscientists Christopher Griffin and Sterling Nesbitt discovered that this sort of variation in growth patterns in people despite their ages also occurred among early dinosaurs, and may have provided an advantage in surviving the harsh environment at the end of the Triassic Period approximately 201 million to 210 million years ago.

The discovery was published in the Proceedings of the National Academy of Sciences.

“We found that the earliest dinosaurs had a far higher level of variation in growth patterns between individuals than crocodiles and birds, their closest living relatives,” said Griffin, of Redding, California, the lead author and a first year doctoral student in the department of geosciences in the College of Science. “Not only were there many different pathways to grow from hatchling to adult, but there was an incredible amount of variation in body size, with some small individuals far more mature than some larger individuals, and some large individuals more immature than we would guess based on size alone.”

The study focused on the skeletal changes that occurred during growth in the small carnivorous dinosaur Coelophysis (SEE-lo-FY-sis), one of the earliest dinosaurs. Hundreds of these animals, ranging from young, immature individuals to older, mature individuals, were buried together by a flooded river about 208 million years ago in present day New Mexico. Griffin examined 174 fossils from this site that are housed within natural history museum collections across North America.

“As these animals grew, muscle attachment scars formed on the limb bones, and the bones of the ankle, hips, and shoulder fused together, similar to how the skull bones of a human baby fuse together during growth,” Griffin said. “Fossils of even a single partial skeleton of an early dinosaur are exceptionally rare, so to have an entire group of a single species that lived and died together provided an unparalleled opportunity to study early dinosaur growth like never before.”

Using a technique known as ontogenetic sequence analysis, Griffin was able to reconstruct the growth sequences of Coelophysis and compare them with two bird and one crocodylian species, ultimately demonstrating that the earliest dinosaurs developed differently than their living relatives.

“Studies like this are a perfect demonstration of how fossils can help us understand the evolution of peculiar features and behaviors of modern animals,” said Steve Brusatte, a paleontologist at the University of Edinburgh who was not involved in the research. “How dinosaurs grew may have been both the key to their early success and the reason that one particular unique subgroup, the birds, survives today.”

This variation in early dinosaurs had been noticed for decades, but had usually been interpreted as a difference between males and females, with one sex identified by large muscle scars and fused bones.

However, statistical tests on the large Coelophysis sample showed no evidence that there were two groups in the sample, as would be expected given variation based on sex, said Griffin. Instead, individuals were arranged on a spectrum ranging from completely lacking scars and fused bones to having all of them, which is what would be expected if these differences were based on growth.

“Large variation in early dinosaurs may have allowed them to survive harsh environmental challenges like dry climate and high levels of carbon dioxide,” said Nesbitt, an assistant professor of geosciences in the College of Science and affiliate with the university’s Global Change Center. “Understanding why dinosaurs were so successful has been a great mystery and high variation may be one of the characteristics of dinosaurs that led to their success. However, it’s difficult to determine whether this trait evolved in response to the environment, or was simply a stroke of luck that allowed these dinosaurs to survive and thrive and become the most dominate vertebrates on Earth for 150 million years.”

Griffin, who graduated with his master’s in geosciences from Virginia Tech in 2016, will continue his Ph.D. work with Nesbitt.

 

Reference:
Christopher T. Griffin, Sterling J. Nesbitt. Anomalously high variation in postnatal development is ancestral for dinosaurs but lost in birds. Proceedings of the National Academy of Sciences, 2016; 201613813 DOI: 10.1073/pnas.1613813113

Note: The above post is reprinted from materials provided by Virginia Tech.

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