Planktonic foraminifera, such as these collected in the Gulf of Mexico, form the base of many marine and aquatic food chains. Upon death, their skeletons settle on the seafloor to form sedimentary rock such as limestone and chalk. Pressed together in sufficient quantities, such sedimentary rock could have a lubricating effect on the movement of continental plates. Credit: Randolph Femmer, USGS
A new study by The University of Texas at Austin has demonstrated a possible link between life on Earth and the movement of continents. The findings show that sediment, which is often comprised from pieces of dead organisms, could play a key role in determining the speed of continental drift. In addition to challenging existing ideas about how plates interact, the findings are important because they describe potential feedback mechanisms between tectonic movement, climate and life on Earth.
The study, published Nov. 15 in Earth and Planetary Science Letters, describes how sediment moving under or subducting beneath tectonic plates could regulate the movement of the plates and may even play a role in the rapid rise of mountain ranges and growth of continental crust.
The research was led by Thorsten Becker, a professor at the UT Jackson School of Geosciences and research scientist at its Institute for Geophysics (UTIG), and Whitney Behr, a research fellow at the Jackson School and professor at ETH Zurich in Switzerland.
Sediment is created when wind, water and ice erode existing rock or when the shells and skeletons of microscopic organisms like plankton accumulate on the seafloor. Sediment entering subduction zones has long been known to influence geological activity such as the frequency of earthquakes, but until now it was thought to have little influence on continental movement. That’s because the speed of subduction was believed to be dependent on the strength of the subducting plate as it bends and slides into the viscous mantle, the semi molten layer of rock beneath the Earth’s crust. Continental movement is driven by one plate sinking under another so, in this scenario, the strength of the portion of the plate being pulled into the Earth’s mantle (and the energy required to bend it) would be the primary control for the speed of the plate movement, with sediment having little effect.
However, prior research involving UTIG scientists had shown the subducting plates may be weaker and more sensitive to other influences than previously thought. This led researchers to look for other mechanisms that might impact plate velocity. They estimated how different types of rock might affect the plate interface ¬- the boundary where subducting plates meet. Subsequent modelling showed that rock made of sediment can create a lubricating effect between plates, accelerating subduction and increasing plate velocity.
This mechanism could set in motion a complex feedback loop. As plate velocity increases, there would be less time for sediment to accumulate, so the amount of subducting sediment would be reduced. This leads to slower subduction, which may allow for mountains to grow at plate boundaries as the force of the two plates running into each other causes uplift. In turn, erosion of those mountains by wind, water and other forces can produce more sediments which feed back into the subduction zone and restart the cycle by increasing the speed of subduction.
“The feedback mechanisms serve to regulate subduction speeds such that they don’t ‘runaway’ with extremely fast velocities,” said Behr.
Behr and Becker’s new model also offers a compelling explanation for variations found in plate speed, such as India’s dramatic northward acceleration some 70 million years ago. The authors propose that as India moved through equatorial seas teeming with life, an abundance of sedimentary rock formed by organic matter settling on the seafloor created a lubricating effect in the subducting plate. India’s march north accelerated from a stately 5 centimeters per year (about 2 inches) to an eye-watering 16 centimeters per year (about 6 inches). As the continent accelerated the amount of sediment being subducted decreased and India slowed before finally colliding with Asia.
Behr and Becker suggest these feedback mechanisms would have been very different in the early Earth before the formation of continents and the emergence of life. Although their model does not examine the origins of these feedback mechanisms, it does raise compelling questions about the interaction between continental movement and life on Earth.
“What is becoming clear is that the geological history of the incoming plate matters,” said Becker, who also holds the Shell Distinguished Chair in Geophysics at UT. “We will have to study in more detail how those possible feedback processes may work.”
Reference:
Whitney M. Behr, Thorsten W. Becker. Sediment control on subduction plate speeds. Earth and Planetary Science Letters, 2018; 502: 166 DOI: 10.1016/j.epsl.2018.08.057
Map of the bedrock topography beneath the ice sheet and the ice-free land surrounding the Hiawatha impact crater. The structure is 31 km wide, with a prominent rim surrounding the structure. In the central part of the impact structure, an area with elevated terrain is seen, which is typical for larger impact craters. Calculations shows that in order to generate an impact crater of this size, the earth was struck by a meteorite more than 1 km wide. Credit: The Natural History Museum of Denmark
An international team lead by researchers from the Centre for GeoGenetics at the Natural History Museum of Denmark, University of Copenhagen have discovered a 31-km wide meteorite impact crater buried beneath the ice-sheet in the northern Greenland. This is the first time that a crater of any size has been found under one of Earth’s continental ice sheets. The researchers worked for last three years to verify their discovery, initially made in the 2015. The research is described in a new study just published in the internationally recognized journal Science Advances.
The crater measures more than 31 km in diameter, corresponding to an area bigger than Paris, and placing it among the 25 largest impact craters on Earth. The crater formed when a kilometre-wide iron meteorite smashed into northern Greenland, but has since been hidden under nearly a kilometre of ice.
“The crater is exceptionally well-preserved, and that is surprising, because glacier ice is an incredibly efficient erosive agent that would have quickly removed traces of the impact. But that means the crater must be rather young from a geological perspective. So far, it has not been possible to date the crater directly, but its condition strongly suggests that it formed after ice began to cover Greenland, so younger than 3 million years old and possibly as recently as 12,000 years ago — toward the end of the last ice age” says Professor Kurt H. Kjær from the Center for GeoGenetics at the Natural History Museum of Denmark.
Giant circular depression
The crater was first discovered in July 2015 as the researchers inspected a new map of the topography beneath Greenland’s ice-sheet. They noticed an enormous, but previously undetected circular depression under Hiawatha Glacier, sitting at the very edge of the ice sheet in northern Greenland.
“We immediately knew this was something special but at the same time it became clear that it would be difficult to confirm the origin of the depression,” says Professor Kjær.
In the courtyard at the Geological Museum in Copenhagen just outside the windows of the Center for GeoGenetics sits a 20-tonne iron meteorite found in North Greenland not far from the Hiawatha Glacier.
“It was therefore not such a leap to infer that the depression could be a previously undescribed meterorite crater, but initially we lacked the evidence,” reflects Associate Professor Nicolaj K. Larsen from Aarhus University.
The crucial evidence
Their suspicion that the giant depression was a meteorite crater was reinforced when the team sent a German research plane from the Alfred Wegener Institute to fly over the Hiawatha Glacier and map the crater and the overlying ice with a new powerful ice radar. Joseph MacGregor, a glaciologist at NASA, who participated in the study and is an expert in ice radar measurements adds:
“Previous radar measurements of Hiawatha Glacier were part of a long-term NASA effort to map Greenland’s changing ice cover. What we really needed to test our hypothesis was a dense and focused radar survey there. Our colleagues at the Alfred Wegener Institute and University of Kansas did exactly that with a next-generation radar system that exceeded all expectations and imaged the depression in stunning detail. A distinctly circular rim, central uplift, disturbed and undisturbed ice layering, and basal debris. It’s all there.”
In the summers of 2016 and 2017, the research team returned to the site to map tectonic structures in the rock near the foot of the glacier and collect samples of sediments washed out from the depression through a meltwater channel.
“Some of the quartz sand washed from the crater had planar deformation features indicative of a violent impact, and this is conclusive evidence that the depression beneath the Hiawatha Glacier is a meteorite crater, ” says Professor Larsen.
The consequences of the impact on the Earth’s climate and life
Earlier studies have shown that large impacts can profoundly affect Earth’s climate, with major consequences for life on Earth at the time. It is therefore very resonable to ask when and how and this meteorite impact at the Hiawatha Glacier affected the planet.
“The next step in the investigation will be to confidently date the impact. This will be a challenge, because it will probably require recovering material that melted during the impact from the bottom of the structure, but this is crucial if we are to understand how the Hiawatha impact affected life on Earth,” concludes Professor Kjær.
Reference:
Kurt H. Kjær, Nicolaj K. Larsen, Tobias Binder, Anders A. Bjørk, Olaf Eisen, Mark A. Fahnestock, Svend Funder, Adam A. Garde, Henning Haack, Veit Helm, Michael Houmark-Nielsen, Kristian K. Kjeldsen, Shfaqat A. Khan, Horst Machguth, Iain McDonald, Mathieu Morlighem, Jérémie Mouginot, John D. Paden, Tod E. Waight, Christian Weikusat, Eske Willerslev, Joseph A. MacGregor. A large impact crater beneath Hiawatha Glacier in northwest Greenland. Science Advances, 2018; 4 (11): eaar8173 DOI: 10.1126/sciadv.aar8173
Slow-motion collisions of tectonic plates under the ocean drag about three times more water down into the deep Earth than previously estimated, according to a first-of-its-kind seismic study that spans the Mariana Trench.
The observations from the deepest ocean trench in the world have important implications for the global water cycle, according to researchers in Arts & Sciences at Washington University in St. Louis.
“People knew that subduction zones could bring down water, but they didn’t know how much water,” said Chen Cai, who recently completed his doctoral studies at Washington University. Cai is the first author of the study published in the Nov. 15 issue of the journal Nature.
“This research shows that subduction zones move far more water into Earth’s deep interior — many miles below the surface — than previously thought,” said Candace Major, a program director in the National Science Foundation’s Division of Ocean Sciences, which funded the study. “The results highlight the important role of subduction zones in Earth’s water cycle.”
“Previous estimates vary widely in the amount of water that is subducted deeper than 60 miles,” said Doug Wiens, the Robert S. Brookings Distinguished Professor in Earth and Planetary Sciences in Arts & Sciences and Cai’s research advisor for the study. “The main source of uncertainty in these calculations was the initial water content of the subducting uppermost mantle.”
To conduct this study, researchers listened to more than one year’s worth of Earth’s rumblings — from ambient noise to actual earthquakes — using a network of 19 passive, ocean-bottom seismographs deployed across the Mariana Trench, along with seven island-based seismographs. The trench is where the western Pacific Ocean plate slides beneath the Mariana plate and sinks deep into the Earth’s mantle as the plates slowly converge.
The new seismic observations paint a more nuanced picture of the Pacific plate bending into the trench — resolving its three-dimensional structure and tracking the relative speeds of types of rock that have different capabilities for holding water.
Rock can grab and hold onto water in a variety of ways.
Ocean water atop the plate runs down into the Earth’s crust and upper mantle along the fault lines that lace the area where plates collide and bend. Then it gets trapped. Under certain temperature and pressure conditions, chemical reactions force the water into a non-liquid form as hydrous minerals — wet rocks — locking the water into the rock in the geologic plate. All the while, the plate continues to crawl ever deeper into the Earth’s mantle, bringing the water along with it.
Previous studies at subduction zones like the Mariana Trench have noted that the subducting plate could hold water. But they could not determine how much water it held and how deep it went.
“Previous conventions were based on active source studies, which can only show the top 3-4 miles into the incoming plate,” Cai said.
He was referring to a type of seismic study that uses sound waves created with the blast of an air gun from aboard an ocean research vessel to create an image of the subsurface rock structure.
“They could not be very precise about how thick it is, or how hydrated it is,” Cai said. “Our study tried to constrain that. If water can penetrate deeper into the plate, it can stay there and be brought down to deeper depths.”
The seismic images that Cai and Wiens obtained show that the area of hydrated rock at the Mariana Trench extends almost 20 miles beneath the seafloor — much deeper than previously thought.
The amount of water that can be held in this block of hydrated rock is considerable.
For the Mariana Trench region alone, four times more water subducts than previously calculated. These features can be extrapolated to predict the conditions under other ocean trenches worldwide.
“If other old, cold subducting slabs contain similarly thick layers of hydrous mantle, then estimates of the global water flux into the mantle at depths greater than 60 miles must be increased by a factor of about three,” Wiens said.
And for water in the Earth, what goes down must come up. Sea levels have remained relatively stable over geologic time, varying by less than 1,000 ft. This means that all of the water that is going down into the Earth at subduction zones must be coming back up somehow, and not continuously piling up inside the Earth.
Scientists believe that most of the water that goes down at the trench comes back from the Earth into the atmosphere as water vapor when volcanoes erupt hundreds of miles away. But with the revised estimates of water from the new study, the amount of water going into the earth seems to greatly exceed the amount of water coming out.
“The estimates of water coming back out through the volcanic arc are probably very uncertain,” said Wiens, who hopes that this study will encourage other researchers to reconsider their models for how water moves back out of the Earth. “This study will probably cause some re-evaluation.”
Moving beyond the Mariana Trench, Wiens along with a team of other scientists has recently deployed a similar seismic network offshore in Alaska to consider how water is moved down into the Earth there.
“Does the amount of water vary substantially from one subduction zone to another, based on the kind of faulting that you have when the plate bends?” Wiens asked. “There’s been suggestions of that in Alaska and in Central America. But nobody has looked at the deeper structure yet like we were able to do in the Mariana Trench.”
Reference:
Chen Cai, Douglas A. Wiens, Weisen Shen, Melody Eimer. Water input into the Mariana subduction zone estimated from ocean-bottom seismic data. Nature, 2018; 563 (7731): 389 DOI: 10.1038/s41586-018-0655-4
Artist depiction of the MMS spacecraft that provided the first view of magnetic reconnection. Credit: NASA/GSFC
Researchers at the University of New Hampshire have captured a difficult-to-view singular event involving “magnetic reconnection” — the process by which sparse particles and energy around Earth collide producing a quick but mighty explosion — in the Earth’s magnetotail, the magnetic environment that trails behind the planet.
Magnetic reconnection has remained a bit of a mystery to scientists. They know it exists and have documented the effects that the energy explosions can have — sparking auroras and possibly wreaking havoc on power grids in the case of extremely large events — but they haven’t completely understood the details. In a study published in the journal Science, the scientists outline the first views of the critical details of how this energy conversion process works in the Earth’s magnetotail.
“This was a remarkable event,” said Roy Torbert of the Space Science Center at UNH and deputy principal investigator for NASA’s Magnetospheric Multiscale mission, or MMS. “We have long known that it occurs in two types of regimes: asymmetric and symmetric but this is the first time we have seen a symmetric process.”
Magnetic reconnection occurs around Earth every day due to magnetic field lines twisting and reconnecting. It happens in different ways in different places, with different effects. Particles in highly ionized gases, called plasmas, can be converted and cause a single powerful explosion, just a fraction of a second long, that can lead to strong streams of electrons flying away at supersonic speeds. The view, which was detected as part of the scientists’ work on the MMS mission, had enough resolution to reveal its differences from other reconnection regimes around the planet like the asymmetric process found in the magnetopause around Earth which is closer to the sun.
“This is important because the more we know and understand about these reconnections,” said Torbert, “the more we can prepare for extreme events that are possible from reconnections around the Earth or anywhere in the universe.”
Magnetic reconnection also happens on the sun and across the universe — in all cases forcefully shooting out particles and driving much of the change we see in dynamic space environments — so learning about it around Earth also helps us understand reconnection in other places in the universe which cannot be reached by spacecraft. The more we understand about different types of magnetic reconnection, the more we can piece together what such explosions might look like elsewhere.
For the first reported asymmetrical event on October 16, 2015, and now this symmetrical event on July 11, 2017, NASA’s MMS mission made history by flying through magnetic reconnection events near the Earth. The four MMS spacecrafts launched from a single rocket were only inside the events for a few seconds, but the instruments which UNH researchers helped to develop were able to gather data at an unprecedented speed of one hundred times faster than ever before. As a result, for the first time, scientists could track the way the magnetic fields changed, new electric fields presented, as well as the speeds and direction of the various charged particles.
Reference:
R. B. Torbert, J. L. Burch, T. D. Phan, M. Hesse, M. R. Argall, J. Shuster, R. E. Ergun, L. Alm, R. Nakamura, K. J. Genestreti, D. J. Gershman, W. R. Paterson, D. L. Turner, I. Cohen, B. L. Giles, C. J. Pollock, S. Wang, L.-J. Chen, J. E. Stawarz, J. P. Eastwood, K. J. Hwang, C. Farrugia, I. Dors, H. Vaith, C. Mouikis, A. Ardakani, B. H. Mauk, S. A. Fuselier, C. T. Russell, R. J. Strangeway, T. E. Moore, J. F. Drake, M. A. Shay, Yuri V. Khotyaintsev, P.-A. Lindqvist, W. Baumjohann, F. D. Wilder, N. Ahmadi, J. C. Dorelli, L. A. Avanov, M. Oka, D. N. Baker, J. F. Fennell, J. B. Blake, A. N. Jaynes, O. Le Contel, S. M. Petrinec, B. Lavraud, Y. Saito. Electron-scale dynamics of the diffusion region during symmetric magnetic reconnection in space. Science, 2018; eaat2998 DOI: 10.1126/science.aat2998
The experiment on La Palma: The laser beam (yellow) generates an artificial guide star in the mesosphere. This light is collected in the receiver telescope (front left). The laser source and the receiver telescope are eight meters away from each other. Credit: Copyright Felipe Pedreros Bustos
The mesosphere, at heights between 85 and 100 kilometers above the Earth’s surface, contains a layer of atomic sodium. Astronomers use laser beams to create artificial stars, or laser guide stars (LGS), in this layer for improving the quality of astronomical observations. In 2011, researchers proposed that artificial guide stars could also be used to measure the Earth’s magnetic field in the mesosphere. An international group of scientists has recently managed to do this with a high degree of precision. The technique may also help to identify magnetic structures in the solid Earth’s lithosphere, to monitor space weather, and to measure electrical currents in the part of the atmosphere called ionosphere.
Astronomers have been using lasers to generate artificial stars for the past 20 years. A laser beam is directed from the ground into the atmosphere. In the sodium layer, it strikes sodium atoms, which absorb the energy of the laser and then start to glow. “The atoms emit light in all directions. Such artificial stars are barely visible to the naked eye but can be observed with telescopes,” explained Felipe Pedreros Bustos of Johannes Gutenberg University Mainz (JGU). In connection with the work on his doctoral thesis, the Chilean-born physicist has spent four years working on the project, which besides JGU involves the European Southern Observatory (ESO), the University of California, Berkeley and Rochester Scientific in the USA, the Italian National Institute for Astrophysics (INAF-OAR), and the University of British Columbia in Vancouver, Canada.
The artificial guide stars help astronomers to correct the distortions of light that travels through the atmosphere. The light from the artificial guide star is collected on the ground by telescopes, and the information is used to adjust in real time state-of-the-art deformable mirrors, compensating the distortions and allowing astronomical objects to be imaged sharply, down to the optical resolution, the so-called diffraction limit, of the telescope.
The precession of sodium atoms reveals the strength of the magnetic field
The participants in the collaborative project are using laser guide stars to measure the Earth’s magnetic field. An ESO LGS unit dedicated to Research and Development is housed in the Roque de los Muchachos Observatory on La Palma, the westernmost Canary Island. The availability and use of the LGS unit has allowed to perform the reported joint experiments, which also aim at increasing the brightness of laser guide stars. From the observatory, a laser beam is directed at the sodium layer which excites and spin-polarizes the atoms making most of their atomic spin point in the same direction. Due to the effect of the surrounding magnetic field, the polarized atomic spins rotate around the direction of the magnetic field similar to the motion of a gyroscope that is tilted from the vertical, a phenomenon known as Larmor precession. “A guide star becomes brighter when the modulation frequency of our laser coincides with the precession frequency of sodium,” explained Pedreros Bustos. “As the Larmor frequency is proportional to the strength of the magnetic field, we can use this method to measure the Earth’s magnetic field in the sodium layer.” The detection scheme is similar to a stroboscope.
Hence, the group has succeeded in using a well-studied, fundamental laboratory technique to observe the natural world. It fills a gap in our knowledge of the Earth’s magnetic field by allowing us to make ground-based observations of the mesosphere, which was previously difficult to access. Up to now, the magnetic field could only be directly measured on the ground, from airplanes, from balloons in the stratosphere, or from satellites.
In May 2018, a US-American research group had published similar findings. However, these latest measurements are much more precise, and scientists hope to improve them still further by using higher-energy lasers. “We can also use the technique to estimate atomic processes in the atmosphere, for example, how often sodium collides with other atoms such as oxygen or nitrogen. This is something that hasn’t been done before,” said Pedreros Bustos.
This artificial guide star measuring technique will be particularly useful in geophysics. It will make it possible to determine changes to the magnetic field of the Earth’s ionosphere caused by solar winds. In addition, observation of oceanic currents and large-scale magnetic structures in the upper mantle would be feasible by means of continuous surveillance of the Earth’s magnetic field at altitudes of 85 to 100 kilometers.
Reference:
Felipe Pedreros Bustos, Domenico Bonaccini Calia, Dmitry Budker, Mauro Centrone, Joschua Hellemeier, Paul Hickson, Ronald Holzlöhner, Simon Rochester. Remote sensing of geomagnetic fields and atomic collisions in the mesosphere. Nature Communications, 2018; 9 (1) DOI: 10.1038/s41467-018-06396-7
The Indus civilization was the largest—but least known—of the first great urban cultures that also included Egypt and Mesopotamia. Named for one of their largest cities, the Harappans relied on river floods to fuel their agricultural surpluses. Today, numerous remains of the Harappan settlements are located in a vast desert region far from any flowing river. Credit: Liviu Giosan, Woods Hole Oceanographic Institution; Stefan Constantinescu, University of Bucharest; James P.M. Syvitski, University of Colorado
More than 4,000 years ago, the Harappa culture thrived in the Indus River Valley of what is now modern Pakistan and northwestern India, where they built sophisticated cities, invented sewage systems that predated ancient Rome’s, and engaged in long-distance trade with settlements in Mesopotamia. Yet by 1800 BCE, this advanced culture had abandoned their cities, moving instead to smaller villages in the Himalayan foothills. A new study from the Woods Hole Oceanographic Institution (WHOI) found evidence that climate change likely drove the Harappans to resettle far away from the floodplains of the Indus.
Beginning in roughly 2500 BCE, a shift in temperatures and weather patterns over the Indus valley caused summer monsoon rains to gradually dry up, making agriculture difficult or impossible near Harappan cities, says Liviu Giosan, a geologist at WHOI and lead author on the paper that published Nov. 13, 2018, in the journal Climate of the Past.
“Although fickle summer monsoons made agriculture difficult along the Indus, up in the foothills, moisture and rain would come more regularly,” Giosan says. “As winter storms from the Mediterranean hit the Himalayas, they created rain on the Pakistan side, and fed little streams there. Compared to the floods from monsoons that the Harappans were used to seeing in the Indus, it would have been relatively little water, but at least it would have been reliable.”
Evidence for this shift in seasonal rainfall — and the Harapans’ switch from relying on Indus floods to rains near the Himalaya in order to water crops — is difficult to find in soil samples. That’s why Giosan and his team focused on sediments from the ocean floor off Pakistan’s coast. After taking core samples at several sites in the Arabian Sea, he and his group examined the shells of single-celled plankton called foraminifera (or “forams”) that they found in the sediments, helping them understand which ones thrived in the summer, and which in winter.
Once he and the team identified the season based on the forams’ fossil remains, they were able to then focus on deeper clues to the region’s climate: paleo-DNA, fragments of ancient genetic material preserved in the sediments.
“The seafloor near the mouth of the Indus is a very low-oxygen environment, so whatever grows and dies in the water is very well preserved in the sediment,” says Giosan. “You can basically get fragments of DNA of nearly anything that’s lived there.”
During winter monsoons, he notes, strong winds bring nutrients from the deeper ocean to the surface, feeding a surge in plant and animal life. Likewise, weaker winds other times of year provide fewer nutrients, causing slightly less productivity in the waters offshore.
“The value of this approach is that it gives you a picture of the past biodiversity that you’d miss by relying on skeletal remains or a fossil record. And because we can sequence billions of DNA molecules in parallel, it gives a very high-resolution picture of how the ecosystem changed over time,” adds William Orsi, paleontologist and geobiologist at Ludwig Maximilian University of Munich, who collaborated with Giosan on the work.
Sure enough, based on evidence from the DNA, the pair found that winter monsoons seemed to become stronger — and summer monsoons weaker — towards the later years of the Harappan civilization, corresponding with the move from cities to villages.
“We don’t know whether Harappan caravans moved toward the foothills in a matter of months or this massive migration took place over centuries. What we do know is that when it concluded, their urban way of life ended,” Giosan says.
The rains in the foothills seem to have been enough to hold the rural Harapans over for the next millennium, but even those would eventually dry up, likely contributing to their ultimate demise.
“We can’t say that they disappeared entirely due to climate — at the same time, the Indo-Aryan culture was arriving in the region with Iron Age tools and horses and carts. But it’s very likely that the winter monsoon played a role,” Giosan says.
The big surprise of the research, Giosan notes, is how far-flung the roots of that climate change may have been. At the time, a “new ice age” was settling in, forcing colder air down from the Arctic into the Atlantic and northern Europe. That in turn pushed storms down into the Mediterranean, leading to an upswing in winter monsoons over the Indus valley.
“It’s remarkable, and there’s a powerful lesson for today,” he notes. “If you look at Syria and Africa, the migration out of those areas has some roots in climate change. This is just the beginning — sea level rise due to climate change can lead to huge migrations from low lying regions like Bangladesh, or from hurricane-prone regions in the southern U.S. Back then, the Harappans could cope with change by moving, but today, you’ll run into all sorts of borders. Political and social convulsions can then follow.”
Also collaborating on the study was Ann G. Dunlea, Samuel E. Munoz, Jeffrey. P. Donnelly, and Valier Galy of WHOI; William D. Orsi of Ludwig-Maximilians-Universität MuÌ?nchen; Marco Coolen and Cornelia Wuchter of Curtin University in Australia; Kaustubh Thirumalai of Brown University; Peter D. Clift of Louisiana State University; and Dorian Q. Fuller of University College, London.
The work was supported by the National Science Foundation’s Division of Ocean Sciences and internal WHOI funds.
Reference:
Liviu Giosan, William D. Orsi, Marco Coolen, Cornelia Wuchter, Ann G. Dunlea, Kaustubh Thirumalai, Samuel E. Munoz, Peter D. Clift, Jeffrey P. Donnelly, Valier Galy, Dorian Q. Fuller. Neoglacial climate anomalies and the Harappan metamorphosis. Climate of the Past, 2018; 14 (11): 1669 DOI: 10.5194/cp-14-1669-2018
A reconstruction of the Eocene of Turkey, where the small marsupial was found. Besides the marsupials, the fauna includes embrithopods (the rhino-like animals of the background, more related to elephants and sea cows), pleuraspidotheriids (primitive ungulates with a deer/dog look), a group of primates called omomyids, bats, tortoises and crocodiles. Credit: Oscar Sanisidro | University of Kansas
Islands have been vital laboratories for advancing evolutionary theory since the pioneering work of Charles Darwin and Alfred Russel Wallace in the 19th century.
Now, a new paper appearing in PLOS ONE from an international team of investigators describes two new fossil relatives of marsupials that shed light on how a unique island ecosystem evolved some 43 million years ago during the Eocene.
“Evolution in many ways is easier to study in an island context than on a large continent like North America because it’s a simpler ecosystem,” said coauthor K. Christopher Beard, Distinguished Foundation Professor of Ecology and Evolutionary Biology at the University of Kansas and senior curator with KU’s Biodiversity Institute and Natural History Museum. “Evolutionary biologists have been focusing on islands ever since Darwin and Wallace independently formulated their ideas about evolution based on their observations of plants and animals living on the Galapagos and the Malay archipelago, which is modern Indonesia.”
However, Beard said a poor fossil record for animals living on islands through “deep time,” or across a multimillion-year time frame, has hampered our understanding of exactly how island ecosystems are assembled. The new paper describes two new fossil species, identified from their teeth, that inhabited the Pontide region of modern-day north-central Turkey.
During the Eocene the Pontide region was an island in a larger version of the modern Mediterranean Sea called Tethys. At that time, Africa and Eurasia were not connected as they are today in the Middle East, but Africa was drifting northward due to plate tectonics and would eventually collide with Eurasia millions of years later. The Pontide region was sandwiched between these converging continents. This geological setting makes the Pontide region similar to the island of Sulawesi in the Indonesian archipelago, which is similarly sandwiched between the converging continents of Asia and Australia.
“No other ecosystem on the face of the planet from any time period matches what we’re finding in the Eocene of Turkey — it’s a completely unique mammalian ecosystem much like Madagascar is today,” he said. “But how did this island biota develop over time? You need fossils and time depth to see that. We’re able here to study in great detail how this ancient island evolved — where the different animals came from, how they got there and when they got there. Once they got there, some of these mammals, including one of the new marsupial lineages we’ve discovered, were able to diversify on the island. Most of the Eocene mammals on the Pontide island seem to have gotten there by swimming or rafting across parts of the Tethys Sea, instead of getting stranded on the island when it got separated from adjacent parts of Eurasia.”
Beard’s collaborators in the research were Grégoire Métais of the Museum national d’Histoire naturelle in Paris, John R. Kappelman of the University of Texas, Alexis Licht of the University of Washington, Faruk Ocakog?lu of Eskis?ehir Osmangazi University in Turkey, and KU’s Pauline M.C. Coster and Michael H. Taylor.
In the Pontide marsupial fossils — which have no living descendants — the team found evidence that distinctive forms of life that develop on islands are ill-fated in general, given enough time.
“One thing we know for sure is that the incredibly interesting and unique Eocene biota that occurred on this island in what is now Turkey at some point was totally eradicated,” Beard said. “It was eradicated when the island was reconnected to mainland Eurasia and more cosmopolitan animals were able to access it for the first time, driving the weird island biota to extinction. The message for conservation biology today is that island ecosystems are inherently ephemeral on the grand scale of macroevolutionary time. Today, conservation biologists are concerned about many endangered taxa on islands. The ugly truth that paleontology provides is that, given enough time, most island faunas are doomed to extinction. They’re cul-de-sacs of evolution — even though they’re wonderful places to study processes of evolution.”
Beard said the two newly described fossil marsupials — Galatiadelphys minor and Orhaniyeia nauta — lived near the top of the food chain on the Pontide of the Eocene, because mammalian carnivores were unable to reach the small island.
“One of weirdest things about the island fauna from the Pontides is that there are no true mammalian carnivores,” he stated. “There was nothing related to cats, dogs, bears or weasels — no modern mammalian predators. They couldn’t get to the Pontide terrain because it was a little island. So, these marsupials ecologically are taking their place at the top of the food chain.”
According to the KU researcher, the newly discovered fossils demonstrate geological context has a huge influence on how ecosystems are assembled on any given island.
“Current ideas about island evolution are based on some fairly simplistic, yet fairly effective, models,” Beard stated. “These models propose that organisms colonize islands based on two main factors — how big is the island and how far away is it from nearby continental landmasses? A bigger island makes a bigger target and hosts a greater diversity of habitats, making it easier for organisms to colonize the island and once they get there they have a better chance of surviving and maybe even diversifying.”
Based on his team’s findings from the Pontide region, Beard said that geological context was at least as important as an island’s size or distance from colonizing animals’ source territory.
“All men may have been created equal, but all islands were not. The geological context of the island — here it’s in a region of active tectonic convergence — we think is swamping these other factors, size and distance to mainland,” he said. “The oddest thing about the Pontide mammal fauna is that it contains a unique mixture of animals coming from Europe, Africa and Asia. Even our two new marsupials show different evolutionary roots in the north and the south. This makes sense because the Pontide island was being sandwiched between Eurasia and Africa, and animals were arriving there from multiple directions. We can make an interesting analogy with the modern island of Sulawesi in Indonesia, which like the Pontide terrain has a mixed fauna. It mainly hosts animals like tarsiers, pigs and shrews that are clearly related to Asian species, but you also have on Sulawesi species that are obviously related to mammals from New Guinea. If you look at plate tectonics today, Sulawesi is getting sandwiched between Australia and Asia in much the same way the Pontide was being sandwiched between Africa and Asia in the Eocene.”
Beard recently returned from Turkey where he and his team conducted more fieldwork. This research was funded by multiple sources including a major grant from the US National Science Foundation.
Reference:
Grégoire Métais, Pauline M. Coster, John R. Kappelman, Alexis Licht, Faruk Ocakoğlu, Michael H. Taylor, K. Christopher Beard. Eocene metatherians from Anatolia illuminate the assembly of an island fauna during Deep Time. PLOS ONE, 2018; 13 (11): e0206181 DOI: 10.1371/journal.pone.0206181
Lijinganthus revoluta embedded in a Myanmar amber. Credit: NIGPAS
About 140 years ago, Charles Darwin seemed to be bothered by evidence suggesting the sudden occurrence of numerous angiosperms in the mid-Cretaceous. Since Darwin’s theory of evolution implies that all organisms should increase gradually, the sudden appearance of angiosperms would have represented a headache in his theory.
Therefore, the sudden occurrence of numerous angiosperms (if seen by Darwin as “the origin of angiosperms”) would rightfully have been mysterious and abominable to him.
Over more than a century of study, however, people have found many angiosperms dating to earlier periods, suggesting the origin of angiosperms was much earlier than the mid-Cretaceous. So what was the phenomenon that bothered Darwin so much?
A group led by Prof. Wang Xin from the Nanjing Institute of Geology and Palaeontology (NIGPAS) of the Chinese Academy of Sciences may have an answer. In the Nov. 13, 2018 online issue of Scientific Reports, the scientists describe a flower, Lijinganthus revoluta, embedded in Burmese amber dating to 99 million years ago (Ma). The fossil is exquisite and complete, including all parts of a perfect pentamerous flower, namely, the calyx, corolla, stamens and gynoecium, and belongs to the pentapetalae of core eudicots.
Together with contemporaneous flowers and fruits, Lijinganthus indicates that core eudicots flourished on earth about 100 Ma. Although this group can be dated back to the Barremian (about 125 Ma) by their characteristic tricolpate pollen grains, eudicots did not dominate vegetation until about 20 million years later (mid-Cretaceous).
Accompanying this core eudicot boom, gnetales and bennettitales underwent rapid decline. Apparently, what bothered Darwin was not the assumed “origin of angiosperms,” but a core eudicot. According to current knowledge of the fossil record, angiosperms originated much earlier.
Reference:
Zhong-Jian Liu et al. The Core Eudicot Boom Registered in Myanmar Amber, Scientific Reports (2018). DOI: 10.1038/s41598-018-35100-4
Reconstruction of a living Mirarce eatoni perched on the horns of the ceratopsian dinosaur Utahceratops gettyi, an animal that lived in Utah during the late Cretaceous 75 million years ago. Credit: Brian Engh illustration
During the late Cretaceous period, more than 65 million years ago, birds belonging to hundreds of different species flitted around the dinosaurs and through the forests as abundantly as they flit about our woods and fields today.
But after the cataclysm that wiped out most of the dinosaurs, only one group of birds remained: the ancestors of the birds we see today. Why did only one family survive the mass extinction?
A newly described fossil from one of those extinct bird groups, cousins of today’s birds, deepens that mystery.
The 75-million-year-old fossil, from a bird about the size of a turkey vulture, is the most complete skeleton discovered in North America of what are called enantiornithines (pronounced en-an-tea-or’-neth-eens), or opposite birds. Discovered in the Grand Staircase-Escalante area of Utah in 1992 by University of California, Berkeley, paleontologist Howard Hutchison, the fossil lay relatively untouched in University of California Museum of Paleontology at Berkeley until doctoral student Jessie Atterholt learned about it in 2009 and asked to study it.
Atterholt and Hutchison collaborated with Jingmai O’Conner, the leading expert on enantiornithines, to perform a detailed analysis of the fossil. Based on their study, enantiornithines in the late Cretaceous were the aerodynamic equals of the ancestors of today’s birds, able to fly strongly and agilely.
“We know that birds in the early Cretaceous, about 115 to 130 million years ago, were capable of flight but probably not as well adapted for it as modern birds,” said Atterholt, who is now an assistant professor and human anatomy instructor at the Western University of Health Sciences in Pomona, California. “What this new fossil shows is that enantiornithines, though totally separate from modern birds, evolved some of the same adaptations for highly refined, advanced flight styles.”
The fossil’s breast bone or sternum, where flight muscles attach, is more deeply keeled than other enantiornithines, implying a larger muscle and stronger flight more similar to modern birds. The wishbone is more V-shaped, like the wishbone of modern birds and unlike the U-shaped wishbone of earlier avians and their dinosaur ancestors. The wishbone or furcula is flexible and stores energy released during the wing stroke.
If enantiornithines in the late Cretaceous were just as advanced as modern birds, however, why did they die out with the dinosaurs while the ancestors of modern birds did not?
“This particular bird is about 75 million years old, about 10 million years before the die-off,” Atterholt said. “One of the really interesting and mysterious things about enantiornithines is that we find them throughout the Cretaceous, for roughly 100 million years of existence, and they were very successful. We find their fossils on every continent, all over the world, and their fossils are very, very common, in a lot of areas more common than the group that led to modern birds. And yet modern birds survived the extinction while enantiornithines go extinct.”
One recently proposed hypothesis argues that the enantiornithines were primarily forest dwellers, so that when forests went up in smoke after the asteroid strike that signaled the end of the Cretaceous — and the end of non-avian dinosaurs — the enantiornithines disappeared as well. Many enantiornithines have strong recurved claws ideal for perching and perhaps climbing, she said.
“I think it is a really interesting hypothesis and the best explanation I have heard so far,” Atterholt said. “But we need to do really rigorous studies of enantiornithines’ ecology, because right now that part of the puzzle is a little hand-wavey.”
Atterholt, Hutchison and O’Connor, who is at the Institute of Vertebrate Paleontology and Paleoanthropology in Beijing, China, published an analysis of the fossil today in the open-access journal PeerJ.
Theropod dinosaurs evolved into birds
All birds evolved from feathered theropods — the two-legged dinosaurs like T. rex — beginning about 150 million years ago, and developed into many lineages in the Cretaceous, between 146 and 65 million years ago.
Hutchison said that he came across the fossil eroding out of the ground in the rugged badlands of the Kaiparowits formation in the Grand Staircase-Escalante National Monument in Garfield County, Utah, just inside the boundary of the recently reduced monument. Having found bird fossils before, he recognized it as a late Cretaceous enantiornithine, and a rare one at that. Most birds from the Americas are from the late Cretaceous (100-66 million years ago) and known only from a single foot bone, often the metatarsus. This fossil was almost complete, missing only its head.
“In 1992, I was looking primarily for turtles,” Hutchison said. “But I pick up everything because I am interested in the total fauna. The other animals they occur with tells me more about the habitat.”
According to Hutchison, the area where the fossil was found dates from between 77 and 75 million years ago and was probably a major delta, like the Mississippi River delta, tropical and forested with lots of dinosaurs but also crocodiles, alligators, turtles and fish.
Unlike most bird fossils found outside America, in particular those from China, the fossil was not smashed flat. The classic early Cretaceous bird, Archaeopteryx, was flattened in sandstone, which preserved a beautiful panoply of feathers and the skeletal layout. Chinese enantiornithines, mostly from the early Cretaceous, are equally beautiful and smashed flatter than a pancake.
“On one hand, it’s great — you get the full skeleton most of the time, you get soft tissue preservation, including feathers. But it also means everything is crushed and deformed,” she said. “Not that our fossils have zero deformation, but overall most of the bones have really beautiful three-dimensional preservation, and just really, really great detail. We see places where muscles and tendons were attaching, all kinds of interesting stuff to anatomists.”
Once Hutchison prepared the fossils and placed them in the UC Museum of Paleontology collection, they drew the attention of a few budding and established paleontologists, but no one completed an analysis.
“The stuff is legendary. People in the vertebrate paleontology community have known about this thing forever and ever, and it just happened that everyone who was supposedly working on it got too busy and it fell by the wayside and just never happened,” Atterholt said. “I was honored and incredibly excited when Howard said that I could take on the project. I was over the moon.”
Her analysis showed that by the late Cretaceous, enantiornithines had evolved advanced adaptations for flying independent of today’s birds. In fact, they looked quite similar to modern birds: they were fully feathered and flew by flapping their wings like modern birds. The fossilized bird probably had teeth in the front of its beak and claws on its wings as well as feet. Some enantiornithines had prominent tail feathers that may have differed between male and female and been used for sexual display.
“It is quite likely that, if you saw one in real life and just glanced at it, you wouldn’t be able to distinguish it from a modern bird,” Atterholt said.
This fossil bird is also among the largest North American birds from the Cretaceous; most were the size of chickadees or crows.
“What is most exciting, however, are large patches on the forearm bones. These rough patches are quill knobs, and in modern birds they anchor the wing feathers to the skeleton to help strengthen them for active flight. This is the first discovery of quill knobs in any enantiornithine bird, which tells us that it was a very strong flier.”
Atterholt and her colleagues named the species Mirarce eatoni (meer-ark’-ee ee-tow’-nee). Mirarce combines the Latin word for wonderful, which pays homage to “the incredible, detailed, three-dimensional preservation of the fossil,” she said, with the mythical Greek character Arce, the winged messenger of the Titans. The species name honors Jeffrey Eaton, a paleontologist who for decades has worked on fossils from the Kaiparowits Formation. Eaton first enticed Hutchison to the area in search of turtles, and they were the first to report fossils from the area some 30 years ago.
Thousands of such fossils from the rocks of the Kaiparowits Formation, many of them dinosaurs, contributed to the establishment of the Grand Staircase-Escalante National Monument in 1996.
“This area contains one of the best Cretaceous fossil records in the entire world, underscoring the critical importance of protecting and preserving these parts of our natural heritage,” Atterholt said. “Reducing the size of the protected area puts some of our nation’s most valuable natural and scientific resources at risk.”
Hutchison’s field work was supported by the Annie M. Alexander endowment to the UCMP.
Reference:
Jessie Atterholt, J. Howard Hutchison, Jingmai K. O’Connor. The most complete enantiornithine from North America and a phylogenetic analysis of the Avisauridae. PeerJ, 2018; 6: e5910 DOI: 10.7717/peerj.5910
Pararhabdodon isonensis. Credit: Oscar Sanisidro / ICP
The Basturs Poble site is what is known in English as a bone bed, a geological stratum containing a great amount of fossils. The stratum dates back some 70 million years. It is the only one to have been found in Europe exclusively containing hadrosaur remains. The excavations conducted during the past ten years have yielded approximately one thousand fossils. The remains are disjointed and possibly belong to only one species: the Pararhabdodon isonensis. “We think the individuals died due to unfavourable environmental conditions, perhaps an extreme dry spell. After their death, the remains got washed away by water and then began to fossilise, but we know that the place where they died was not far away from the site,” explains Víctor Fondevilla, researcher at the Institut Català de Paleontologia Miquel Crusafont (ICP) and the Universitat Autònoma de Barcelona (UAB) and first author of the paper.
The research recently published in PLOS ONE analysed the 270 fossil remains at the site which were prepared to be studied, including skulls, jaws, teeth, vertebrae and limb bones. Researchers however did not have enough with describing and measuring each specimen, they also analysed the interior of the fossils to extract information on the age of each individual. “We can cut open the fossils and analyse their inner structure. It gives us a lot of information on the vital cycle of each of the animals,” says ICREA research lecturer at ICP Meike Köhler. Similar to the rings of trees, in sections of elongated bones we find lines of arrested growth (LAGs) which are indicators corresponding to the alternation between favourable and unfavourable periods. In this way we can calculate at what age they died.
Using this system, palaeontologists detected that at the site were a large number of young individuals and, to a lesser extent, sub-adults and adults. But no recently hatched dinosaur fossils were found. “We estimated that the youngest individuals died at two years of age and that the adults were 14 to 15,” Fondevilla explains. The fact that researchers found so many young samples makes them think that the accumulation of bones at Basturs Poble represents a natural population of herbivores, where young individuals are more abundant. “It may also be that the abundance of young remains is due to these individuals being more vulnerable to crises and therefore dying in larger quantities than adults would,” the main researcher of the study comments.
Also participating in the study were researchers from the Museum of Conca Dellà and the Friulian Museum of Natural History in Udine, Italy.
Hadrosaurs, A Well-Known Group in Catalonia
Hadrosaurs, also known as “duck-billed” dinosaurs, are a group of ornithischian herbivorous dinosaurs which lived in the Late Cretaceous period. This is probably the most well-known group of dinosaurs. Among the subfamilies there are the lambeosaurines, which can be found in Catalonia’s sites. They characteristically had a robust medium to large-sized body (weighing one kilogramme when hatching and reaching up to 3000 kilogrammes as adults), with smaller front limbs and larger hind limbs. This last trait made it possible for them to walk on two or four feet indifferently.
The skull is long and duck-billed shaped, and the jaw holds rows of stacked teeth. Their most distinctive characteristic was their cranial crest, formed by several more or less developed cranial bones. What the crest was used for remains unclear, but scientists believe it could have acted as a resonating chamber with which to amplify sounds and facilitate recognising members of the same species. Other hypotheses point to the possibility of only males having crests which aimed to attract the females.
The Pararhabdodon isonensis species is only known to have existed in the Pallars Jussà region. [nbsp]The species was described in 1985 after the discovery of remains found at Sant Romà d’Abella and its specific name — isonensis — refers to the town of Isona located near the site. These dinosaurs measured from 6 to 7 metres in length and it is estimated that the adults weighed some three tonnes.
The Pyrenees, Home to the Last Dinosaurs in Europe
Catalonia is very rich in fossiliferous sediment. Of the most relevant are the pre-Pyrennean basins, which conserve remains of different life forms from the Late Cretaceous Period (between 70 and 66 million years ago). In geological terms, that is very shortly before the great extinction which marked the end of many life forms, including non-avian dinosaurs. Located at the Pyrennean sites, therefore, are the last dinosaurs to have lived in Europe, a few hundreds of years before they disappeared from the world entirely.
The Basturs Poble site was located by scientific communicator Marc Boada in August 2001. Upon discovering fossils on the surface, he contacted palaeontologists from the Museum of Conca Dellà. Few months later a palaeontology dig was conducted which confirmed the exceptional nature of this site. After a first research dig, twelve more campaigns have been conducted as part of research projects led by Àngel Galobart, Head of the Mesozoic Fauna Research Group at ICP, and Rodrigo Gaete from the Museum of Conca Dellà.
The fossils found at Basturs Poble are conserved at the Museum of Conca Dellà. The museum’s dinosaur exhibition hall contains a sample of the most outstanding bones found at the site and a life-size recreation of a Pararhabdodon isonensis dinosaur.
Reference:
Víctor Fondevilla, Fabio Marco Dalla Vecchia, Rodrigo Gaete, Àngel Galobart, Blanca Moncunill-Solé, Meike Köhler. Ontogeny and taxonomy of the hadrosaur (Dinosauria, Ornithopoda) remains from Basturs Poble bonebed (late early Maastrichtian, Tremp Syncline, Spain). PLOS ONE, 2018; 13 (10): e0206287 DOI: 10.1371/journal.pone.0206287
Dinosaur blood vessel with adjacent bone matrix that still contains bone cells. These structures have a perfect morphological preservation over hundreds of millions of years, but are chemically transformed through oxidative crosslinking. The extract comes from a sauropod dinosaur. Credit: Jasmina Wiemann/Yale University
Burnt toast and dinosaur bones have a common trait, according to a new, Yale-led study. They both contain chemicals that, under the right conditions, transform original proteins into something new. It’s a process that may help researchers understand how soft-tissue cells inside dinosaur bones can survive for hundreds of millions of years.
A research team from Yale, the American Museum of Natural History, the University of Brussels, and the University of Bonn announced the discovery Nov. 9 in the journal Nature Communications.
Fossil soft tissue in dinosaur bones has been a controversial topic among researchers for quite some time. Hard tissues, such as bones, eggs, teeth, and enamel scales, are able to survive fossilization extremely well. Soft tissues, such as blood vessels, cells, and nerves — which are stored inside the hard tissue — are more delicate and thought to decay rapidly after death. These soft tissues are composed mainly of proteins, which are believed to completely degrade within about four million years.
Yet dinosaur bones are much older, roughly 100 million years old, and they occasionally preserve organic structures similar to cells and blood vessels. Various attempts to resolve this paradox have failed to provide a conclusive answer.
“We took on the challenge of understanding protein fossilization,” said Yale paleontologist Jasmina Wiemann, the study’s lead author. “We tested 35 samples of fossil bones, eggshells, and teeth to learn whether they preserve proteinaceous soft tissues, find out their chemical composition, and determine under what conditions they were able to survive for millions of years.”
The researchers discovered that soft tissues are preserved in samples from oxidative environments such as sandstones and shallow, marine limestones. The soft tissues were transformed into Advanced Glycoxidation and Lipoxidation end products (AGEs and ALEs), which are resistant to decay and degradation. They’re also structurally comparable to chemical compounds that stain the dark crust on toast.
AGEs and ALEs are characterized by a brownish color that stains fossil bones and teeth that contain them. The compounds are hydrophobic, which means they are resistant to the normal effects of water, and have properties that make it difficult for bacteria to consume them.
Wiemann and her colleagues made their discovery by decalcifying fossils and imaging the released soft tissue structures. They applied Raman microspectroscopy — a non-destructive method for analyzing both the inorganic and organic contents of a sample — to the extracted fossil soft tissues. During this process, laser energy directed at the tissue causes molecular vibrations that carry spectral fingerprints for the chemicals that are present.
Co-author Derek Briggs, Yale’s G. Evelyn Hutchinson Professor of Geology and Geophysics and a curator at the Yale Peabody Museum of Natural History, said the study points to localities where soft tissue may be found in fossil bones, including sandstones deposited from rivers, dune sands, and shallow marine limestones.
“Our results show how chemical alteration explains the fossilization of these soft tissues and identifies the types of environment where this process occurs,” Briggs said. “The payoff is a way of targeting settings in the field where this preservation is likely to occur, expanding an important source of evidence of the biology and ecology of ancient vertebrates.”
Additional co-authors of the study are Matteo Fabbri from Yale, Martin Sander and Tzu-Ruei Yang from the University of Bonn, Koen Stein from the University of Brussels, and Mark Norell from the American Museum of Natural History.
Reference:
Jasmina Wiemann, Matteo Fabbri, Tzu-Ruei Yang, Koen Stein, P. Martin Sander, Mark A. Norell, Derek E. G. Briggs. Fossilization transforms vertebrate hard tissue proteins into N-heterocyclic polymers. Nature Communications, 2018; 9 (1) DOI: 10.1038/s41467-018-07013-3
Note: The above post is reprinted from materials provided by Yale University. Original written by Jim Shelton.
Extraction of the sequence in Basa de la Mora lake by the IPE-CSIC research group of Quaternary Paleoenvironments. Credit: Anchel Belmonte Creative Commons BY-ND
Remains of chironomid subfossils, a type of insects similar to mosquitoes, were used in a study by researchers from the University of Barcelona, the Pyrenean Ecology Institute (IPE-CSIC), and the University of Bern, to reconstruct the temperature of the Iberian Peninsula in the Holocene, the geological period that goes from 11,000 years ago until now. The results of the study prove some of the climate patterns of the Holocene brought by other methodologies: a rise of temperatures in the beginning and the end of the period, higher temperatures during the Holocene Climate Optimum and a decline of temperatures after the beginning of the Late Holocene. The study, published in the journal The Holocene, is the first reconstruction of the temperature of the peninsula during this period using this indicator. According to the researchers, this is a promising tool to understand the evolution of climate over history and the main natural and anthropic climate changes that shaped ecosystems before instrumental records.
Participants in the study are the researcher Pol Tarrats, member of the research group Freshwater Ecology, Hydrology and Management (FEHM) of the UB and first author of the article, and the researchers Miguel Cañedo-Argüelles, Narcís Prat and Maria Rieradevall, from the same group; Blas Valero-Garcés and Penélope González-Sampériz, from the Pyrenean Institute of Ecology (IPE-CSIC), and Oliver Heiri, from the University of Bern (Switzerland).
Paleoclimate indicators in larval phase
Chironomidae are from the nematocera family (diptera order), similar to mosquitoes. These insects are abundant worldwide and change gender and amount depending on the temperature in which they live, so they are a good indicator of this climate variable. The research study was conducted in Basa de la Mora lake (Huesca), where researchers took the necessary sediments to carry the study out. “Regarding the records of Chironomidae, the aim of any paleoenvironmental reconstruction study is to get the larval cephalic capsules, since this is the larval phase of the insects that is developed in the sediments and that from which subfossil remains are obtained,” says Miguel Cañedo-Argüelles, postdoctoral researcher from the Department of Evolutionary Biology, Ecology and Environmental of the UB. Subfossils are biological remains whose fossilization process is not complete due the way these were buried in the sediment and still have organic matter which can be analysed.
These were taken by the IPE-CSIC Research Group of Quaternary Paleoenvironments to get a sequence covering the whole Holocene period. The approximation of temperatures is obtained by comparing the composition of insects taken from the sediment sample over the sequence of the study, with a calibration basis made of many samples of Chironomidae that are taken in the present which are associated with temperature changes. “In our case, we did not have that comparing element which is common in the study area (Pyrenees), so the sequence we got in Basa de la Mora lake was compared to the results of a study, the most developed and used one in Europe, conducted in 274 lakes in Switzerland and Norway,” says Pol Tarrats.
Regional differences regarding other reconstructions
The results of the study show a temperature rise in the beginning of the Holocene, reaching the highest values in the Holocene Climate Optimum (about 7,800 years ago). There are also high temperatures until about 6,000 years ago, when a decline of temperature started and led to the lowest values in the first stage of the late Holocene (about 4,200 and 2,000 years ago).
Last, researchers detected a rise of temperatures over the two last millenniums, but they state they have to be careful with these data. “We cannot guarantee the observed rise in the reconstruction results from a temperature rise only, we cannot rule out other variables that can influence at other levels, such as the gradual increase of the anthropic activity in the area, which can change the community of Chironomidae to species that adapt to higher temperatures, but there are also human influence indicators,” says Narcís Prat.
Although these conclusions can coincide with other paleoclimate reconstructions, results also highlight some divergences at a regional level. “These differences can occur due the fact that some indicators point out to different seasonal signs. Therefore, Chironomidae are indicators of temperature in summer, while others such as chrysophites or alkenones are related to winter/spring temperatures,” notes the researcher.
A tool to evaluate climate trends
Climate reconstruction of the past in general and temperatures in particular is a relevant tool when evaluating current climate trends within the context of climate change. For researchers, the methodology they use in this study is “an interesting tool to contrast, confirm and disprove patterns on evolution of temperature in the Holocene, as well as adding other indicators to reconstruct temperatures to advance in this study field.”
In this sense, the aim of the research team is to develop a comparing basis to link the present Chironomidae communities in different geographical areas of the Iberian Peninsula with temperature. “This would allow us, on the one hand, confirm the influence of temperature when explaining the distribution of different species, and on the other, to use specific transfer functions for each area, which would provide a higher precision and strength to the next studies on reconstructing temperatures out of Iberian Peninsula Chironomidae,” concludes Miguel Cañedo-Argüelles.
Reference:
Pol Tarrats, Oliver Heiri, Blas Valero-Garcés, Miguel Cañedo-Argüelles, Narcís Prat, Maria Rieradevall, Penélope González-Sampériz. Chironomid-inferred Holocene temperature reconstruction in Basa de la Mora Lake (Central Pyrenees). The Holocene, 2018; 28 (11): 1685 DOI: 10.1177/0959683618788662
Xenothrix’s close relative, the red titi monkey (Callicebus cupreus). Credit: ZSL
Analysis of ancient DNA of a mysterious extinct monkey named Xenothrix — which displays bizarre body characteristics very different to any living monkey — has revealed that it was in fact most closely related to South America’s titi monkeys (Callicebinae). Having made their way overwater to Jamaica, probably on floating vegetation, their bones reveal they subsequently underwent remarkable evolutionary change.
The research published today in Proceedings of the National Academy of Sciences (12 November 2018) and carried out by a team of experts from international conservation charity ZSL (Zoological Society of London), London’s Natural History Museum (NHM), and the American Museum of Natural History in New York, also reveals that monkeys must have colonised the Caribbean islands more than once. The study reports an incredible discovery of how the unusual ecology of islands can dramatically influence animal evolution.
Xenothrix, unlike any other monkey in the world, was a slow-moving tree-dweller with relatively few teeth, and leg bones somewhat like a rodent’s. Its unusual appearance has made it difficult for scientists to work out what it was related to and how it evolved. However, the scientific team have successfully extracted the first ever ancient DNA from an extinct Caribbean primate — uncovered from bones excavated in a Jamaican cave and providing important new evolutionary insights.
Professor Samuel Turvey from ZSL, a co-author on the paper, said: “This new understanding of the evolutionary history of Xenothrix shows that evolution can take unexpected paths when animals colonise islands and are exposed to new environments. However, the extinction of Xenothrix, which evolved on an island without any native mammal predators, highlights the great vulnerability of unique island biodiversity in the face of human impacts.”
Professor Ian Barnes, whom runs the NHM’s ancient DNA lab, and co-author said: “Recovering DNA from the bones of extinct animals has become increasingly commonplace in the last few years. However, it’s still difficult with tropical specimens, where the temperature and humidity destroy DNA very quickly. I’m delighted that we’ve been able to extract DNA from these samples and resolve the complex history of the primates of the Caribbean.”
It is likely that Xenothrix’s ancestors colonised Jamaica from South America around 11 million years ago, probably after being stranded on natural rafts of vegetation that were washed out of the mouths of large South American rivers. Many other animals, such as large rodents called hutias (Capromyidae) that still survive on some Caribbean islands today, probably colonised the region in the same way.
Ross MacPhee of the American Museum of Natural History’s Mammalogy Department, a co-author of the study, said: “Ancient DNA indicates that the Jamaican monkey is really just a titi monkey with some unusual morphological features, not a wholly distinct branch of New World monkey. Evolution can act in unexpected ways in island environments, producing miniature elephants, gigantic birds, and sloth-like primates. Such examples put a very different spin on the old cliché that ‘anatomy is destiny.'”
What Xenothrix may have looked like has been greatly debated, with suggestions that it looked like a kinkajou (Potos) or a night monkey (Aotus). Living titi monkeys are small tree-dwelling monkeys found across tropical South America, with long soft red, brown, grey or black fur. They are active during the day, extremely territorial and vocal, and live up to 12 years in the wild, with the father often caring for the young.
Though the Galapagos Islands are famous for inspiring Charles Darwin’s theory of evolution, the islands of the Caribbean have also been home to some of the most unusual and mysterious species to have ever evolved. However, the Caribbean has also experienced the world’s highest rate of mammal extinction since the end of the last ice age glaciation, likely caused by hunting and habitat loss by humans, and predation by invasive mammals brought by early settlers.
Reference:
Roseina Woods, Samuel T. Turvey, Selina Brace, Ross D. E. MacPhee, Ian Barnes. Ancient DNA of the extinct Jamaican monkey Xenothrix reveals extreme insular change within a morphologically conservative radiation. Proceedings of the National Academy of Sciences, 2018; 201808603 DOI: 10.1073/pnas.1808603115
UNLV geologist Stephen Rowland discovered that a set of 28 footprints left behind by a reptile-like creature 310 million years ago are the oldest ever to be found in Grand Canyon National Park. Credit: Stephen Rowland
A geology professor at the University of Nevada, Las Vegas, has discovered that a set of 28 footprints left behind by a reptile-like creature 310 million years ago, are the oldest ever to be found in Grand Canyon National Park.
The fossil trackway covers a fallen boulder that now rests along the Bright Angel Trail in the national park. Rowland presented his findings at the recent annual meeting of the Society of Vertebrate Paleontology.
“It’s the oldest trackway ever discovered in the Grand Canyon in an interval of rocks that nobody thought would have trackways in it, and they’re among the earliest reptile tracks on earth,” said Rowland.
Rowland said he’s not prepared to say that they’re the oldest tracks of their kind ever discovered, but it’s a possibility, as he’s still researching the discovery.
“In terms of reptile tracks, this is really old,” he said, adding that the tracks were created as the supercontinent Pangaea was beginning to form.
Rowland was first alerted to the tracks in spring 2016 by a colleague who was hiking the trail with a group of students. The boulder ended up along the trail after the collapse of a cliff.
A year later, Rowland studied the footprints up close.
“My first impression was that it looked very bizarre because of the sideways motion,” Rowland said. “It appeared that two animals were walking side-by-side. But you wouldn’t expect two lizard-like animals to be walking side-by-side. It didn’t make any sense.”
When he arrived home, he made detailed drawings, and began hypothesizing about the “peculiar, line-dancing gait” left behind by the creature.
“One reason I’ve proposed is that the animal was walking in a very strong wind, and the wind was blowing it sideways,” he said.
Another possibility is that the slope was too steep, and the animal sidestepped as it climbed the sand dune. Or, Rowland said, the animal was fighting with another creature, or engaged in a mating ritual.
“I don’t know if we’ll be able to rigorously choose between those possibilities,” he said.
He plans to publish his findings along with geologist Mario Caputo of San Diego State University in January. Rowland also hopes that the boulder is soon placed in the geology museum at the Grand Canyon National Park for both scientific and interpretive purposes.
Meanwhile, Rowland said that the footprints could belong to a reptile species that has never yet been discovered.
“It absolutely could be that whoever was the trackmaker, his or her bones have never been recorded,” Rowland said.
Earth’s water may have originated from both asteroidal material and gas left over from the formation of the Sun, according to new research. The new finding could give scientists important insights about the development of other planets and their potential to support life.
In a new study in the Journal of Geophysical Research: Planets, a journal of the American Geophysical Union, researchers propose a new theory to address the long-standing mystery of where Earth’s water came from and how it got here.
The new study challenges widely-accepted ideas about hydrogen in Earth’s water by suggesting the element partially came from clouds of dust and gas remaining after the Sun’s formation, called the solar nebula.
To identify sources of water on Earth, scientists have searched for sources of hydrogen rather than oxygen, because the latter component of water is much more abundant in the solar system.
Many scientists have historically supported a theory that all of Earth’s water came from asteroids because of similarities between ocean water and water found on asteroids. The ratio of deuterium, a heavier hydrogen isotope, to normal hydrogen serves as a unique chemical signature of water sources. In the case of Earth’s oceans, the deuterium-to-hydrogen ratio is close to what is found in asteroids.
But the ocean may not be telling the entire story of Earth’s hydrogen, according to the study’s authors.
“It’s a bit of a blind spot in the community,” said Steven Desch, a professor of astrophysics in the School of Earth and Space Exploration at Arizona State University in Tempe, Arizona and co-author of the new study, led by Peter Buseck, Regents’ Professor in the School of Earth and Space Exploration and School of Molecular Sciences at Arizona State University. “When people measure the [deuterium-to-hydrogen] ratio in ocean water and they see that it is pretty close to what we see in asteroids, it was always easy to believe it all came from asteroids.”
More recent research suggests hydrogen in Earth’s oceans does not represent hydrogen throughout the entire planet, the study’s authors said. Samples of hydrogen from deep inside the Earth, close to the boundary between the core and mantle, have notably less deuterium, indicating this hydrogen may not have come from asteroids. Noble gases helium and neon, with isotopic signatures inherited from the solar nebula, have also been found in the Earth’s mantle.
In the new study, researchers developed a new theoretical model of Earth’s formation to explain these differences between hydrogen in Earth’s oceans and at the core-mantle boundary as well as the presence of noble gases deep inside the planet.
Modeling Earth’s beginning
According to their new model, several billion years ago, large waterlogged asteroids began developing into planets while the solar nebula still swirled around the Sun. These asteroids, known as planetary embryos, collided and grew rapidly. Eventually, a collision introduced enough energy to melt the surface of the largest embryo into an ocean of magma. This largest embryo would eventually become Earth.
Gases from the solar nebula, including hydrogen and noble gases, were drawn in by the large, magma-covered embryo to form an early atmosphere. Nebular hydrogen, which contains less deuterium and is lighter than asteroidal hydrogen, dissolved into the molten iron of the magma ocean.
Through a process called isotopic fractionation, hydrogen was pulled towards the young Earth’s center. Hydrogen, which is attracted to iron, was delivered to the core by the metal, while much of the heavier isotope, deuterium, remained in the magma which eventually cooled and became the mantle, according to the study’s authors. Impacts from smaller embryos and other objects then continued to add water and overall mass until Earth reached its final size.
This new model would leave Earth with noble gases deep inside its mantle and a lower deuterium-to-hydrogen ratio in its core than in its mantle and oceans.
The authors used the model to estimate how much hydrogen came from each source. They concluded most was asteroidal in origin, but some of Earth’s water did come from the solar nebula.
“For every 100 molecules of Earth’s water, there are one or two coming from solar nebula,” said Jun Wu, assistant research professor in the School of Molecular Sciences and School of Earth and Space Exploration at Arizona State University and lead author of the study.
An insightful model
The study also offers scientists new perspectives about the development of other planets and their potential to support life, the authors said. Earth-like planets in other solar systems may not all have access to asteroids loaded with water. The new study suggests these exoplanets could have obtained water through their system’s own solar nebula.
“This model suggests that the inevitable formation of water would likely occur on any sufficiently large rocky exoplanets in extrasolar systems,” Wu said. “I think this is very exciting.”
Anat Shahar, a geochemist at the Carnegie Institution for Science, who was not involved with the study, noted the hydrogen fractionation factor, which describes how the deuterium-to-hydrogen ratio changes when the element dissolves in iron, is currently unknown and difficult to measure. For the new study, this property of hydrogen had to be estimated.
The new model, which fits in well with current research, could be tested once experiments reveal the hydrogen fractionation factor, Shahar said.
“This paper is a very creative alternative to what is an old problem,” Shahar said. “The authors have done a good job of estimating what these different fractionation factors would be without having the experiments.”
Reference:
Jun Wu, Steven J. Desch, Laura Schaefer, Linda T. Elkins-Tanton, Kaveh Pahlevan, Peter R. Buseck. Origin of Earth’s Water: Chondritic Inheritance Plus Nebular Ingassing and Storage of Hydrogen in the Core. Journal of Geophysical Research: Planets, 2018; DOI: 10.1029/2018JE005698
The skull of the holotype specimen of C. parvus (JLUM L0304-j-Zn2). Credit: Chen et al., 2018 CC-BY
The teeth of Changchunsaurus parvus, a small herbivorous dinosaur from the Cretaceous of China, represent an important and poorly-known stage in the evolution of ornithopod dentition, according to a study released November 7, 2018 in the open-access journal PLOS ONE by Jun Chen of Jilin University in China and colleagues.
Ornithischian (“bird-hipped”) dinosaurs developed an incredible diversity of teeth, including the famously complex dental batteries of derived ornithopods, but little is known about how these intricate arrangements arose from the simple tooth arrangements of early dinosaurs. Changchunsaurus parvus belongs to an early branch at or near the origins of the ornithopods, and thus may provideinsight into the ancestral state of ornithopod tooth development. In this study, Chen and colleagues took thin sections from five jaw bones of Changchunsaurus to investigate tooth composition as well as how the teeth are maintained throughout the life of the animal using histological techniques.
Among the notable features of Changchunsaurus dentition is a unique method of tooth replacement that allowed it to recycle teeth without disrupting the continuous shearing surface formed by its tooth rows. The authors also found that the teeth feature wavy enamel, a tissue type formerly thought to have evolved only in more derived ornithopods. The authors suspect these features may have arisen early on as this group of dinosaurs became specialized for herbivory.
Features of the jaws and teeth are often used to assess dinosaur phylogeny. In addition to investigating the evolution of ornithopod dentition, this study also identifies new dental traits that might help sort out ornithischian relationships in future analyses. But the authors note that this is only the first in-depth study at a dinosaur near the base of the ornithopod family tree, and that more studies on more dinosaurs will be needed to fill in the full picture of this group’s evolution.
Professor Chen Jun summarizes: “These tissue-level details of the teeth of Changchunsaurus tell us that their teeth were well-adapted to their abrasive, plant-based diets. Most surprisingly, the wavy enamel described here, presumably to make it more resistant to wear, was previously thought to be exclusive to their giant descendants, the duckbilled dinosaurs.”
Reference:
Jun Chen, Aaron R. H. LeBlanc, Liyong Jin, Timothy Huang, Robert R. Reisz. Tooth development, histology, and enamel microstructure in Changchunsaurus parvus: Implications for dental evolution in ornithopod dinosaurs. PLOS ONE, 2018; 13 (11): e0205206 DOI: 10.1371/journal.pone.0205206
Note: The above post is reprinted from materials provided by PLOS.
An international team of scientists from Leicester, Yale, Oxford and London has discovered a rare and exceptionally well-preserved tiny crustacean in 430 million-years-old rocks in Herefordshire, UK. The fossil is a new species of ostracod, a relative of crabs and shrimps and is just a few millimetres long.
This particular fossil preserves not just the animal’s hard shell but also its limbs, eyes, gut and gills. Examples of exceptional preservation in ostracods, in which soft-parts are also preserved in the fossil record, are exceedingly rare. The respiratory system includes five pairs of gills with canals that in life conveyed essential fluids. The implication is that a heart had likely evolved in representatives of this common group of micro-crustaceans by at least 430 million years ago
The specimen has been given the name Spiricopia aurita, from the Latin words for ‘breath of life’, ‘abundance’ and ‘ears’.
Professor David Siveter, from the University of Leicester’s School of Geography, Geology and the Environment, said: “This is an exciting and rare find, in which the soft parts of the animal are preserved as well as its shell. In almost all cases such fleshy structures are denied to the fossil record. It gives us a tantalising window into the palaeobiology of the animal and here yields knowledge about important organ-systems and associated metabolic activities in what is a widespread group of fossil and living arthropods.”
lived in a sea that covered much of southern Britain and beyond during the Silurian period (about 443-420 million years ago). An influx of volcanic ash entombed the animals living there and they were fossilised and preserved intact within hard calcareous nodules.
The fossil was recovered from its host rock using a digital reconstruction technique that involves grinding down the actual fossil and rock, layer by wafer-thin layer, and then producing a virtual fossil. The research has been published in the Royal Society journal Biology Letters.
Reference:
David J. Siveter et al. A well-preserved respiratory system in a Silurian ostracod, Biology Letters (2018). DOI: 10.1098/rsbl.2018.0464
Teeth of Simiolus minutus, which currently reside in the National Museum of Kenya, Nairobi, were found in the Tugen Hills of Kenya. Credit: Stony Brook University
When Stony Brook University anthropologist James Rossie began sifting through sediment in the Tugen Hills of Kenya during his first day of the dig, he didn’t know he’d discover teeth from a previously undiscovered tiny ape species.
Now, a study authored by Rossie and his former doctoral advisor, the late Andrew Hill of Yale University, shows that this belongs to a new species of ape—the smallest ever yet described, weighing just under 3.5 kilograms—from 12.5 million year old sites in the Tugen Hills, giving important clues about the unexplained decline in diversity of apes during the Miocene epoch. The paper, titled “A new species of Simiolus from the middle Miocene of the Tugen Hills, Kenya,” is scheduled to published in the December issue of the Journal of Human Evolution.
The fossil molars were found at three different sites along the Tugen Hills and Lake Baringo Basin by Rossie and Hill in 2004, just more than a decade before Hill’s death in 2015. Rossie said fossil molars from the tiny ape, now housed in the National Museum of Kenya, Nairobi, show evidence of leaf eating, which suggests that it was in direct competition with the earliest colobine monkeys for food resources. Rossie said the small ape is also the latest-surviving member yet described of the small apes that flourished in the early Miocene epoch.
At the beginning of the Miocene epoch, there were only a few species of monkeys, while apes were represented by a broad radiation of species ranging from 4 to 50 kilograms; today, however, there are only a handful of ape species remaining. Precisely what caused the decrease in ape diversity and rise of monkey diversity is a mystery that paleontologists have been contemplating for decades, Rossie said, and many suspect that direct competition between the two groups was to blame.
“One thing this shows us is that some apes were leaning toward folivory [leaf eating] at just the time when monkeys were evolving their uniquely effective adaptations for it,” said Rossie, . “Under those circumstances, I’m not surprised that this is the last you see of these small apes. We’ve previously found the earliest colobine monkeys at these sites, and now we have an ape that looks like it would have been in direct competition with them for food.”
Rossie, an associate professor of anthropology in the College of Arts and Sciences, said fossil molars from the tiny ape, now housed in the National Museum of Kenya, Nairobi, show evidence of leaf eating, which suggests that it was in direct competition with the earliest colobine monkeys for food resources. Rossie said the small ape is also the latest-surviving member yet described of the small apes that flourished in the early Miocene epoch.
The greatest obstacle to solving this puzzle is the relative scarcity of fossil sites in the middle of the transition, Rossie said – from about 14 to 6 Ma. The new species comes from sites in the Tugen Hills that are among a small number of African sites in this time range.
Reference:
James B. Rossie et al. A new species of Simiolus from the middle Miocene of the Tugen Hills, Kenya, Journal of Human Evolution (2018). DOI: 10.1016/j.jhevol.2018.09.002
The wavy appearance of the enamel of Changchunsaurus in thin section and under cross-polarized light. Credit: University of Toronto Mississauga
Two new research papers take a bite out of the mysteries around how early dinosaurs and mammals evolved their unique tooth replacement and anchoring systems.
The studies, involving Professor Robert Reisz, a paleontologist at the University of Toronto Mississauga, appear in the latest issues of PLOS ONE and the Proceedings of the Royal Society B.
In the first paper, Reisz and his colleagues at Jilin University in China examined the teeth of Changchunsaurus parvus, a small herbivorous dinosaur from the Cretaceous period.
Ornithischian (“bird-hipped”) dinosaurs developed an incredible diversity of teeth, including the complex dental batteries of derived ornithopods (like the famous duck-bill dinosaurs), but little is known about how these intricate arrangements arose from the simple tooth arrangements of early dinosaurs. Changchunsaurus parvus belongs to a branch at or near the origins of the ornithopods, and thus may provide insight into early ornithopod tooth development.
In this study, Reisz and his colleagues found a unique method of tooth replacement that allowed Changchunsaurus to recycle teeth without disrupting the continuous shearing surface formed by its tooth rows. The authors also found that the teeth feature wavy enamel, a tissue type formerly thought to have evolved only in more modern ornithopods. The authors suspect these features may have arisen early on as this group of dinosaurs became specialized for eating plants.
The whole tooth: how mammals evolved their unique tooth anchoring system
In the second study, published in the Proceedings of the Royal Society B, Reisz worked with his students who are now at the University of Alberta and the University of British Columbia, as well as collaborators at the University of Washington in Seattle, and the Unidad Ejecutora Lillo in Argentina.
Any person who has worn braces knows that your teeth can slowly be pushed and pulled into their proper spots. What you may not know is that this movement is made possible by a special ligament that holds each tooth in its socket. This ligament also serves to cushion each tooth as we chew our food. The origins of this ligament, however, have been a mystery.
This study, led by former University of Toronto Mississauga PhD student Aaron LeBlanc, has solved the mystery surrounding how mammals evolved their complex tooth-anchoring system. For over a hundred years, scientists thought that this ligament evolved with the earliest mammals when they first began to chew, but this new paper shows that this system appeared first in the extinct relatives of mammals, called the therapsids.
By examining CT scans and making thin sections of fossil therapsid teeth and jaws for microscopic study, LeBlanc and his colleagues found that mammal teeth are not as unusual as we once thought. “We found evidence for this ligament system in several groups of extinct therapsids, telling us that it evolved before the first mammals were chewing their food,” says LeBlanc.
The researchers also think they’ve figured out how our therapsid ancestors evolved this ligament anchoring system. They found that in many of the fossil synapsid jaws, the teeth were rapidly fused in place by this encroaching bone, but in some therapsids, the surrounding bone grew more slowly.
“We found that some therapsids, like mammals, must have evolved this ligament anchoring system not by developing brand new tissues, but by delaying the growth of the surrounding bone,” says Reisz. “We’ve re-framed how we view the mammalian condition. We don’t think that mammals are more ‘advanced’ than the other extinct therapsids, but instead mammal teeth are frozen in an earlier state of development compared to animals that have teeth fused to the jaws.”
Both studies undertaken at the University of Toronto Mississauga involve teeth that are not firmly anchored to the jaws, but rather held in place by ligaments. There is now clear evidence that ligaments are present in both carnivorous and herbivorous dinosaurs and mammals, and these ligaments are not necessarily related to the evolution of chewing, as previously thought. Reisz hopes that ongoing research will continue to reveal a better understanding of this interesting enigma.
Reference:
Chen J, LeBlanc ARH, Jin L, Huang T, Reisz RR (2018) Tooth development, histology, and enamel microstructure in Changchunsaurus parvus: Implications for dental evolution in ornithopod dinosaurs. PLoS ONE 13(11): e0205206. DOI: 10.1371/journal.pone.0205206
The layer of the Earth we live on is broken into a dozen or so rigid slabs (called tectonic plates by geologists) that are moving relative to one another. Credit: USGS
Scientists from Germany’s Kiel University and British Antarctic Survey (BAS) have used data from the European Space Agency (ESA), Gravity field and steady-state Ocean Circulation Explorer (GOCE) mission to unveil key geological features of the Earth’s lithosphere — the rigid outer layer that includes the crust and the upper mantle.
Published this week in the journal Scientific Reports the study is a step forward in the quest to image the structure and setting of different continents using satellite gravity data, including Antarctica, the least understood piece of the whole plate tectonic puzzle. Satellite gravity provides a new tool to link the remote and ice-covered continent with the rest of the Earth. This improves our understanding of Antarctica’s deep structure, which is particularly important, as the properties of its lithosphere can also influence the overlying ice sheets.
GOCE measures differences in horizontal and vertical components of the gravity field — known as gradients. These gradients can be complex to interpret and so the authors combined these to produce simpler ‘curvature images’ that reveal large-scale tectonic features of the Earth more clearly.
Lead author, Prof. Jörg Ebbing from the Kiel University said: “Our new satellite gravity gradient images improve our knowledge of Earth’s deep structure. The satellite gravity data can be combined with seismological data to produce more consistent images of the crust and upper mantle in 3D. This is crucial to understanding how plate tectonics and deep mantle dynamics interact.”
Fausto Ferraccioli, Science Leader of Geology and Geophysics at the British Antarctic Survey and co-author of the study, said, “Satellite gravity is revolutionizing our ability to study the lithosphere of the entire Earth, including its least understood continent, Antarctica. In East Antarctica, for example, we now begin to see a more complex mosaic of ancient lithosphere provinces. GOCE shows us fundamental similarities but also unexpected differences between its lithosphere and other continents, to which it was joined until 160 million years ago.”
The new study presents a view of the Earth’s continental crust and upper mantle not previously achievable using global seismic models alone. The authors noted that, despite their similar seismic characteristics, there are contrasts in the gravity signatures for ancient parts of the lithosphere (known as cratons), indicating differences in their deep structure and composition. These features are important. Because they form the oldest cores of the lithosphere, they hold key records of Earth’s early history.
Reference:
Jörg Ebbing, Peter Haas, Fausto Ferraccioli, Folker Pappa, Wolfgang Szwillus, Johannes Bouman. Earth tectonics as seen by GOCE – Enhanced satellite gravity gradient imaging. Scientific Reports, 2018; 8 (1) DOI: 10.1038/s41598-018-34733-9
