Modern volcanism tied to events occurring soon after Earth's birth

Plumes of hot magma from the volcanic hotspot that formed Réunion Island in the Indian Ocean rise from an unusually primitive source deep beneath Earth's surface, according to new work in Nature from Carnegie's Bradley Peters, Richard Carlson, and Mary Horan along with James Day of the Scripps Institution of Oceanography.

A fieldwork photo from Réunion Island shows the flank of the Cirque de Cilaos,
looking out towards the Indian Ocean [Credit: Bradley Peters]

Réunion marks the present-day location of the hotspot that 66 million years ago erupted the Deccan Traps flood basalts, which cover most of India and may have contributed to the extinction of the dinosaurs. Flood basalts and other hotspot lavas are thought to originate from different portions of Earth's deep interior than most volcanoes at Earth's surface and studying this material may help scientists understand our home planet's evolution.

The heat from Earth's formation process caused extensive melting of the planet, leading Earth to separate into two layers when the denser iron metal sank inward toward the center, creating the core and leaving the silicate-rich mantle floating above.

Over the subsequent 4.5 billion years of Earth's evolution, deep portions of the mantle would rise upwards, melt, and then separate once again by density, creating Earth's crust and changing the chemical composition of Earth's interior in the process. As crust sinks back into Earth's interior -- a phenomenon that's occurring today along the boundary of the Pacific Ocean -- the slow motion of Earth's mantle works to stir these materials, along with their distinct chemistry, back into the deep Earth.

Sunrise over the summit of Piton des Neiges, the extinct volcano on the Indian Ocean's Réunion Island
[Credit: Bradley Peters]

But not all of the mantle is as well-blended as this process would indicate. Some older patches still exist -- like powdery pockets in a poorly mixed bowl of cake batter. Analysis of the chemical compositions of Réunion Island volcanic rocks indicate that their source material is different from other, better-mixed parts of the modern mantle.

Using new isotope data, the research team revealed that Réunion lavas originate from regions of the mantle that were isolated from the broader, well-blended mantle. These isolated pockets were formed within the first ten percent of Earth's history.

Isotopes are elements that have the same number of protons, but a different number of neutrons. Sometimes, the number of neutrons present in the nucleus make an isotope unstable; to gain stability, the isotope will release energetic particles in the process of radioactive decay. This process alters its number of protons and neutrons and transforms it into a different element. This new study harnesses this process to provide a fingerprint for the age and history of distinct mantle pockets.

Looking into down into a volcanic crater of Piton de la Fournaise on Réunion Island
with dormant volcanic cones in the background [Credit: Bradley Peters]

Samarium-146 is one such unstable, or radioactive, isotope with a half-life of only 103 million years. It decays to the isotope neodymium-142. Although samarium-146 was present when Earth formed, it became extinct very early in Earth's infancy, meaning neodymium-142 provides a good record of Earth's earliest history, but no record of Earth from the period after all the samarium-146 transformed into neodymium-142. Differences in the abundances of neodymium-142 in comparison to other isotopes of neodymium could only have been generated by changes in the chemical composition of the mantle that occurred in the first 500 million years of Earth's 4.5 billion-year history.

The ratio of neodymium-142 to neodymium-144 in Réunion volcanic rocks, together with the results of lab-based mimicry and modeling studies, indicate that despite billions of years of mantle mixing, Réunion plume magma likely originates from a preserved pocket of the mantle that experienced a compositional change caused by large-scale melting of Earth's earliest mantle.

The team's findings could also help explain the origin of dense regions right at the boundary of the core and mantle called large low shear velocity provinces (LLSVPs) and ultralow velocity zones (ULVZs), reflecting the unusually slow speed of seismic waves as they travel through these regions of the deep mantle. Such regions may be relics of early melting events.

"The mantle differentiation event preserved in these hotspot plumes can both teach us about early Earth geochemical processes and explain the mysterious seismic signatures created by these dense deep-mantle zones," said lead author Peters.

Source: Carnegie Institution for Science [February 28, 2018]

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Flipside of a dinosaur mystery: 'Bloat-and-float' explains belly-up ankylosaur fossils

A scientist with the Canadian Museum of Nature has answered a long-standing mystery about why fossils of ankylosaurs -- the "armoured tanks" of the dinosaur world -- are mainly found belly-side up. In doing so, he has ruled out three other competing theories involving clumsiness, predation, and the effects of bloating as seen in armadillo roadkills.

Illustration of Euoplocephalus, an ankylosaur. Ankylosaurids are sometimes called 
the 'tanks of the Cretaceous' given their squat bodies and armored hides 
[Credit: Brett Booth Brett Booth]

Palaeontologist Dr. Jordan Mallon says the evidence points to a phenomenon called "bloat-and-float," whereby the bloating carcasses of ankylosaurs would end up in a river, flip belly-side up due to the weight of their heavy armour, and then float downstream. The remains would wash ashore, where decomposition and then fossilization would seal the dinosaur remains in their upside-down death pose.

"Textbooks have touted that ankylosaur fossils are usually found upside down, but no one has gone back and checked the records to make sure that's the case," explains Mallon. The observations date from the 1930s. Indeed, the fossils of two star ankylosaurs described in 2017, Borealopelta from Alberta and Zuul from Montana, were found upside down.

Mallon examined 32 ankylosaur fossils from Alberta (of which 26 were found belly up), photos of specimens, field notes, and other signs such as erosion of the exposed surface, sun bleaching, and the presence of lichens.

The results are published in the online journal Palaeogeography, Palaeoclimatology, Palaeoecology. Collaborators included armadillo experts Drs. Colleen McDonough and Jim Loughry of Valdosta State University in Georgia, and Dr. Don Henderson, with Drumheller Alberta's Royal Tyrrell Museum of Palaeontology.

Mallon ruled out three other theories before settling on "bloat-and-float" to explain the preponderance of the belly-up remains.

"One idea was that ankylosaurs were simply clumsy, tripping over themselves or rolling down hills and ending up dying that way," he says. But since ankylosaurs existed for about 100 million years, clumsy habits would not fit with their apparent evolutionary success.

Another theory was that ankylosaurs were prey for carnivores, such as hungry tyrannosaurids, which would flip the armoured dinosaurs onto their backs to get at the soft underbelly. "If this was true, we would expect to see signs of bite marks, especially on upside-down ones, but we saw marks on only one specimen," explains Mallon. "Since they were armoured, it makes sense that ankylosaurs were not regularly preyed upon, and the fossil evidence in museum collections supports this."

The third idea, proposed in the 1980s, is an analogy to what happens with some armadillo roadkills -- as the carcass rots and bloats, gas accumulates, and the limbs would splay out, eventually rolling the animal onto its back.

The challenge was to test this hypothesis. Enter McDonough and Loughry who are experts on modern armadillos, which also have an armoured shell. Over the summer of 2016, they studied 174 examples of dead armadillo. "Sure enough, the data show that they do not occur more often on their backs," says Mallon. The pair even examined dead armadillos placed in plexiglass cases in their backyard to keep away scavengers. Regardless of the positioning of the carcasses, bloating did not cause them to roll over onto their backs.

That left the "bloat-and-float" hypothesis as the most likely explanation for the presence of upside-down fossils. To study this, Mallon turned to computer simulations developed by Dr. Don Henderson, who specializes in the floating behaviour of animals in water.

Ankylosaur fossils in North America are found in river channel deposits, and in the Late Cretaceous Period these animals would have been living along a coastline of what is known as the Western Interior Seaway.

"We designed these models of ankylosaurs, both clubless and clubbed, and looked at their floating behavior," explains Mallon. The computer modelling showed that the animals would tend to flip upside down quite easily in water. Nodosaurids, which are ankylosaurs with no tail clubs, would flip most easily at the slightest tilt; the ankyosaurids (with clubbed tails), were more stable but could still be flipped.

"So 'bloat-and-float'" fits with their known environment, and this research helps inform about the transport behavior of dead dinosaurs, which is important to know when studying fossil ecosystems. Ultimately, this is a classic case study of the scientific method: examining alternative hypotheses, finding ways to test them, and ruling them out one-by-one. What you are left with at the end is the most likely explanation."

Source: Canadian Museum of Nature [February 28, 2018]

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Miniscule flightless birds have lived in New Zealand's wetlands for millions of years

Fossilized bones of two new species of tiny, flightless extinct birds have been discovered by Australasian scientists in 19 to 16-million-year-old sediments of an ancient lake on the South Island of New Zealand.

A tiny extinct rail (30-40g) is overshadowed by a regular duck 
[Credit: Gavin Mouldey]

The two miniscule species—one barely larger than a sparrow—were members of the rail family, a group of birds common today in wetlands that includes swamphens, moorhens, coots and crakes. Their remains were unearthed near the town of St Bathans in Central Otago.

Many rail species can fly well and have dispersed to far-flung oceanic islands. However, flightlessness has evolved more times in this group of birds that in any other, especially on predator-free islands. The world's largest rails evolved in New Zealand, notably the flightless takahe and weka.

The study, led by scientists from Flinders University with colleagues from UNSW, Canterbury Museum and the Museum of New Zealand, is published in the Journal of Systematic Palaeontology.

Team member UNSW Professor Mike Archer, says: "This new discovery emphasizes the fact that New Zealand has long been one of the world's most extraordinary engines driving bird evolution.

"Charting how lineages like these rails have changed through time on an island that has been geographically isolated for more than 80 million years will test basic presumptions made about bird evolution in general," says Professor Archer of the of the PANGEA Research Centre in the School of Biological, Earth and Environmental Sciences.

Nineteen to 16 million years ago, a 5600 square kilometre megalake dominated the landscape of New Zealand's South Island. It was surrounded by a subtropical rainforest and plants typical of Australia and long lost from New Zealand, such as eucalypts, casuarinas, palms and cycads, were common there.

"Flightlessness in birds is often associated with an increase in size," says Ellen Mather, study lead author and Ph.D. student at Flinders University. "The weka, which is in the same family as our fossil birds and lives in New Zealand today, is about the size of a chicken. The Banded Rail, their closest flying relative, is about half that size."

The most common of the new fossil rails has been named Priscaweka parvales, meaning ancient weka with small wings. It was a mere one twentieth of the weight of a weka and was similar in size to the recently extinct Chatham rail Cabalus modestus.

Small flightless birds only exist in the absence of terrestrial mammalian predators, and New Zealand has long been recognised as the iconic example of a country with an avifauna which evolved in the absence of such predators.

When humans discovered New Zealand, the main islands had many flightless birds including giants within the nine species of moa, several kiwi, two huge geese, two adzebills, even some tiny wrens, and at least five flightless rails.

Team member, Dr. Paul Scofield, a Senior Curator at the Natural History at Canterbury Museum, says: "The new St Bathans' rails join a host of other fossil birds recovered from these deposits that show New Zealand has long been a land of birds. The discovery of these two miniscule flightless rails raises the question of 'Where did they come from?'"

The researchers suggest they had ancestors in Australia which flew across the 1500 km ocean to New Zealand in previous millennia. However, the new species are unlike any rail known elsewhere, so their exact origin or closest relatives remain a mystery.

Other than hints of large flightless moa ancestors, these rails are the first flightless birds to be described from this fauna. This is unexpected as the St Bathans Fauna contains small terrestrial mammals, which normally preclude evolution of small flightless species. The tiny flightless rails therefore strongly suggest that the mysterious mammals were not predators of small birds. Flightless birds have been a feature of the New Zealand avifauna for millions of years, much longer than previously thought. They are probably the oldest flightless rails known globally.

"The ongoing research into the fossil birds of New Zealand builds on that begun over 150 years ago. It continues to throw up revelations into the timing and origins of major groups of birds that characterize modern avifaunas" says Associate Professor Trevor Worthy of Flinders University.

Source: University of New South Wales [February 28, 2018]

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Geologists solve fossil mystery by creating 3-D 'virtual tour' through rock

Have you ever wished you could travel inside a rock? It may sound more like magic than science, but Princeton scientists have found a way to make it (almost) true.

With an industrial grinder, a super-high-resolution camera usually used for wedding photography, and high-speed neural
networks, Princeton geoscientists Adam Maloof and Akshay Mehra can deconstruct rock samples and create three-
dimensional digital versions, which they have used to analyze specimens of Cloudina fossils gathered by Mehra (left)
and undergraduates Will Van Cleve and Christian Gray (right) of the Class of 2017 from the Byng Formation,
a fossil reef formation in a glacier-carved valley on Salient Mountain in the Canadian Rockies
[Credit: Adam Maloof and Akshay Mehra, Princeton University Department of Geosciences]

With an industrial grinder and a super-high-resolution camera, Princeton geoscientists Adam Maloof and Akshay Mehra can deconstruct rock samples and create three-dimensional digital versions that scientists can look at from any angle. In addition, they have developed software that allows the computer to segment images and isolate objects without human bias.

Using this technology in conjunction with detailed field observations, they examined a thin-shelled creature that lived over much of the world about 545 million years ago, Cloudina, generally agreed to be the first-ever "biomineralizer," an organism that can create a shell or bones in addition to soft tissue.

While previous researchers had argued that Cloudina were reef builders, Maloof and Mehra were able to use their 3-D reconstruction of the creatures' delicate tube-like structures to conclude that the fossils had been transported from other areas, suggesting that Cloudina played only a minor role in the earliest reef systems. Their work appears in the current issue of the Proceedings of the National Academy of Sciences.

"I thought going in we would learn all sorts about this amazing first biomineralizer and first reef builder, but Cloudina turned out to be more like a reef dweller," said Maloof, an associate professor of geosciences. He has now turned his focus to the next-oldest potential reef builder, a sponge called Archaeocyathid that lived about 520 million years ago.

Cloudina had proven resistant to detailed study because its delicate casing is too fragile to extract physically from the surrounding limestone, and it could not be imaged remotely with traditional X-ray tomography techniques, which require density differences between the object of interest and the surrounding material. Because Cloudina is chemically identical to limestone, the fossils were effectively invisible to X-rays.

Meet GIRI

Almost five years ago, Maloof a nd Situ Studio collaborator Brad Samuels assembled the technology to create what he now calls "flipbooks," digital renderings that move through more than a thousand wafer-thin slices through a rock. Known as "GIRI" or "the grinder," the Princeton Grinding Imaging and Reconstruction Instrument is an answer to geologists' long-standing desire to know what rocks look like on the inside.

Princeton University geoscientist Adam Maloof has spent five years perfecting a combination grinder and imaging system
that can create a three-dimensional 'virtual tour' through the inside of any solid object, from rocks to batteries. Here,
a diamond wheel grinds a sample in the Princeton Grinding Imaging and Reconstruction Instrument (GIRI) in the
Grinder Lab behind Guyot Hall, Princeton University [Credit: Adam Maloof and Akshay Mehra,
Princeton University Department of Geosciences]

"Forever -- since Darwin -- people have tried to figure out how fossils look in 3-D, when they're embedded in rock and it's hard to get them out," Maloof said. "People did serial sections just like this way back then -- but perhaps not at this scale -- where they would grind away a little rock, draw it, grind a little more, draw it. ... It can be incredibly time-consuming."

Enter GIRI, which can cut slices as thin as a few microns (less than 1 percent of a millimeter) and can run 24 hours a day for weeks on end. As each slice takes about 90 seconds to cut and image, researchers have to choose between speed and scale. Most of the specimens Maloof and Mehra have imaged are cut into 30-micron slices, about a third the thickness of a human hair. A typical inch-thick, 1,500-slice sample takes about a day and a half to grind and image; during this time, the operator needs to replace machine fluids and clean the wipers (which clear the surface after each cut) only once.

"The process is destructive," Maloof said. "Dinosaur bones, lunar samples -- there are certain specimens that people are less likely to give us. It hasn't really stopped us, because most samples are not precious. Cloudina, there are zillions of them -- we could never grind them all."

GIRI can produce a 3-D rendering of any solid object, whether or not it has the density differences needed for effective X-ray computed microtomography (usually known as X-ray CT or Micro CT). In addition, because you're taking a super-high-resolution photograph with every slice, you're always seeing the rock itself, not just the density model that remote sensing can provide.

"It's destructive of course, that's the disadvantage, but what's so nice is that you get to see photographs and make direct observations," Maloof. "That's what's been so life-changing to me: I love that it's not a model. You can just see it. On any given slice, if you find something great, you can just find the slice and say, 'What did it look like?' ...We're on a virtual tour inside, rather than looking at waveforms and trying to interpret them."

Once ranging throughout Australian and New Guinea, the Tasmanian tiger disappeared from the mainland around 3000 years ago, likely due to competition with humans and dingos.

The remaining Tasmanian tiger population, isolated on Tasmania, was hunted to extinction in the early 20th century, with the last known individual dying at Hobart Zoo in 1936.

Axel Newton, PhD student and Lead Author on the paper notes, until now there have only been limited details on its growth and development. For the very first time we have been able to look inside these remarkably rare and precious specimens.

Unable to study the living species, the team had to look to the 13 Tasmanian tiger joey specimens that exist in museum collections worldwide, including three from the collection of Museums Victoria. These joey specimens, representing five stages of postnatal development, were scanned using non-invasive X-ray micro-CT scanning technology to create high resolution 3D digital models, in which all their internal structures such as skeleton and organs could be studied.

Associate Professor Andrew Pask from the University of Melbourne explains this was an incredibly effective technique to study the skeletal anatomy of the specimens without causing any damage to them.

"This research clearly demonstrates the power of CT technology. It has allowed us to scan all the known Thylacine joey specimens in the world, and study their internal structures in high resolution without having to dissect or cause damage to the specimen. By examining their bone development, we’ve been able to illustrate how the Tasmanian tiger matured and identify when they took on the appearance of a dog."

The study has also revealed the incorrect classification of two specimens held in the collection of the Tasmanian Museums and Art Gallery (TMAG). Instead, they are most likely to be quolls or Tasmanian devils, based on the number of vertebrate and presence of large epipubic bones (specialised bones that support the pouch in modern marsupials).

Tasmanian tiger [Credit: Tasmanian Museum and Art Gallery, Hobart, Tasmania]

Senior Curator of Vertebrate Zoology at TMAG, Ms Kathryn Medlock, said that the museum had received many requests to dissect its pouch young over the years but requests were always refused.

"One of the major advantages of this new technology is that it has enabled us to do research and answer many questions without destruction of the sample specimens. This is a significant advancement that also has an additional benefit of helping us to learn more about the identity of these specimens that have been in the TMAG collection for many years."

An exciting outcome of the research is that the 3D digital Tasmanian tiger models are to be made publicly available as a resource for current and future researchers.

Source: The University of Melbourne [February 21, 2018]

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Locomotion of bipedal dinosaurs might be predicted from that of ground-running birds

A new model based on ground-running birds could predict locomotion of bipedal dinosaurs based on their speed and body size, according to a study published in the open-access journal PLOS ONE by Peter Bishop from the Queensland Museum, Australia and colleagues.

Ground-running bird model may predict bipedal dinosaur locomotion
[Credit: Peter Bishop, Queensland Museum]

Previous research has investigated the biomechanics of ground-dwelling birds to better understand the how bipedal non-avian dinosaurs moved, but it has not previously been possible to empirically predict the locomotive forces that extinct dinosaurs experienced, especially those species that were much larger than living birds. Bishop and colleagues examined locomotion in 12 species of ground-dwelling birds, ranging in body mass from 45g to 80kg, as the birds moved at various speeds along enclosed racetracks while cameras recorded their movements and forceplates measured the forces their feet exerted upon the ground.

The researchers found that many physical aspects of bird locomotion change continuously as speed increases. This supports previous evidence that unlike humans, who have distinct "walking" and "running" gaits, birds move in a continuum from "walking" to "running". The authors additionally observed consistent differences in gait and posture between small and large birds.

The researchers used their data to construct the biomechanically informative, regression-derived statistical (BIRDS) Model, which requires just two inputs - body mass and speed - to predict basic features of bird locomotion, including stride length and force exerted per step. The model performed well when tested against known data. While more data are needed to improve the model, and it is unclear if it can be extrapolated to animals of much larger body mass, the researchers hope that it might help predict features of non-avian dinosaur locomotion using data from fossils and footprints.

Source: Public Library of Science [February 21, 2018]

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