WFS

Formation of sedimentary layers of white clay, Tamilnadu, India

Fossil site for wood fossils, Tamilnadu, India

Fossil site in Kerala, India

Fossil wood park maintained by geological survey of India at Tamilnadu

Cretaceous fossil sites india

Fossils in rack:-Cyad

Fossils in rack:-echiniderms

Fossils in rack:-Rastellum sp

Pre-historic seabed, Cretaceous period

Some Volcanoes ‘Scream’ at Ever Higher Pitches Until They Blow Their Tops

July 20th, 2013

Riffin

It is not unusual for swarms of small earthquakes to precede a volcanic eruption. They can reach a point of such rapid succession that they create a signal called harmonic tremor that resembles sound made by various types of musical instruments, though at frequencies much lower than humans can hear.

A new analysis of an eruption sequence at Alaska’s Redoubt Volcano in March 2009 shows that the harmonic tremor glided to substantially higher frequencies and then stopped abruptly just before six of the eruptions, five of them coming in succession.

“The frequency of this tremor is unusually high for a volcano, and it’s not easily explained by many of the accepted theories,” said Alicia Hotovec-Ellis, a University of Washington doctoral student in Earth and space sciences.

Redoubt Volcano’s active lava dome as it appeared on May 8, 2009. The volcano is in the Aleutian Range about 110 miles south-southwest of Anchorage, Alaska. (Credit: Chris Waythomas, Alaska Volcano Observatory)

Documenting the activity gives clues to a volcano’s pressurization right before an explosion. That could help refine models and allow scientists to better understand what happens during eruptive cycles in volcanoes like Redoubt, she said.

The source of the earthquakes and harmonic tremor isn’t known precisely. Some volcanoes emit sound when magma — a mixture of molten rock, suspended solids and gas bubbles — resonates as it pushes up through thin cracks in Earth’s crust.

But Hotovec-Ellis believes in this case the earthquakes and harmonic tremor happen as magma is forced through a narrow conduit under great pressure into the heart of the mountain. The thick magma sticks to the rock surface inside the conduit until the pressure is enough to move it higher, where it sticks until the pressure moves it again.

Each of these sudden movements results in a small earthquake, ranging in magnitude from about 0.5 to 1.5, she said. As the pressure builds, the quakes get smaller and happen in such rapid succession that they blend into a continuous harmonic tremor.

“Because there’s less time between each earthquake, there’s not enough time to build up enough pressure for a bigger one,” Hotovec-Ellis said. “After the frequency glides up to a ridiculously high frequency, it pauses and then it explodes.”

She is the lead author of a forthcoming paper in the Journal of Volcanology and Geothermal Research that describes the research. Co-authors are John Vidale of the UW and Stephanie Prejean and Joan Gomberg of the U.S. Geological Survey.

Hotovec-Ellis is a co-author of a second paper, published online July 14 in Nature Geoscience, that introduces a new “frictional faulting” model as a tool to evaluate the tremor mechanism observed at Redoubt in 2009. The lead author of that paper is Ksenia Dmitrieva of Stanford University, and other co-authors are Prejean and Eric Dunham of Stanford.

The pause in the harmonic tremor frequency increase just before the volcanic explosion is the main focus of the Nature Geoscience paper. “We think the pause is when even the earthquakes can’t keep up anymore and the two sides of the fault slide smoothly against each other,” Hotovec-Ellis said.

She documented the rising tremor frequency, starting at about 1 hertz (or cycle per second) and gliding upward to about 30 hertz. In humans, the audible frequency range starts at about 20 hertz, but a person lying on the ground directly above the magma conduit might be able to hear the harmonic tremor when it reaches its highest point (it is not an activity she would advise, since the tremor is closely followed by an explosion).

Scientists at the USGS Alaska Volcano Observatory have dubbed the highest-frequency harmonic tremor at Redoubt Volcano “the screams” because they reach such high pitch compared with a 1-to-5 hertz starting point. Hotovec-Ellis created two recordings of the seismic activity. A 10-second recording covers about 10 minutes of seismic sound and harmonic tremor, sped up 60 times. A one-minute recording condenses about an hour of activity that includes more than 1,600 small earthquakes that preceded the first explosion with harmonic tremor.

Upward-gliding tremor immediately before a volcanic explosion also has been documented at the Arenal Volcano in Costa Rica and Soufrière Hills volcano on the Caribbean island of Montserrat.

“Redoubt is unique in that it is much clearer that that is what’s going on,” Hotovec-Ellis said. “I think the next step is understanding why the stresses are so high.”

The work was funded in part by the USGS and the National Science Foundation.

Rare Fossils Found On Brisbane Building Site

July 19th, 2013

Riffin

Australian builders have uncovered a rare trove of crocodile, frog, fish and plant fossils, in what could be a world-first.

50 million year old fossil find Brisbane — The fossils relate to the period after dinosaurs died out. Pic: tenNews

The fossils, trapped in a layer of oil shale, were found during excavation works near Brisbane’s Geebung railway station at a depth of about 15 metres (49ft).

The bones have been identified as coming from ancient crocodiles, as well as other significant material including fish, freshwater shells and plant impressions.

They are thought to be about 50 million years old.

The find – a significant insight into how animals and plants evolved after the extinction of dinosaurs – has been described as a “potential world-first”.

Queensland Museum chief executive Suzanne Miller told Australia’s Ten News: “In the whole of north Australia this is absolutely unique, and dependent on what we find, because we are just at the beginning of this project, this could be unique in the world.

“These could be some of the earliest mammals ever found.”

Geoscientists are currently examining the fossils.

Ms Miller added: “Very few sites of this age are available for study, as similar-aged sites in the greater Brisbane area are often no longer accessible due to housing and urban development.

“The construction works have fortuitously provided access to a new locality that was not previously known to palaeontologists.”

Queensland transport minister Scott Emerson said it was an “extraordinary finding in Brisbane’s backyard” and the area would be combed for further specimens.

“The fossils will provide a valuable opportunity for more detailed studies,” Mr Emerson said, adding that experts were interested in retrieving any other fossils that could be in the same area.

Queensland has some of Australia’s richest fossil deposits, including a famous dinosaur dig at Winton in the west of the state, where three new dinosaur species were discovered in 2009.

Brisbane is Australia’s third largest city, with a population of 2.2 million.

Rare Fossil of Late Cretaceous Plesiosaur Discovered

July 18th, 2013

Riffin

University of Alabama researchers have discovered the fossilized remains of a large marine reptile that once ruled the open seas 80 million years ago.

The initial discovery, made June 20 by middle-school student Noah Traylor during a UA-hosted expedition, was later identified as part of a large neck vertebra of an elasmosaur, which is a subgroup of the late Cretaceous plesiosaurs.

Elasmosaurid plesiosaurs are easily recognized by their large body size — some species reach up to 45 feet in length.

“Think Loch Ness monster,” said Dr. Dana Ehret, UA Museum paleontologist. “They have very large flippers for swimming and extremely long necks, consisting of up to about 70 neck vertebrae.”

Plesiosaurs became extinct by the end of Cretaceous, or about 65.5 million years ago, and they are generally rare in the fossil record for Alabama. This is only the second elasmosaurid specimen containing more than one or two bones found in the state, Ehret said. The first, which consists of 22 vertebrae, was found in the late 1960s and is now part of UA Collections.

An artist rendering of an elasmosaur, created by University of Alabama undergraduate student Asher Albein. (Credit: University of Alabama)

This discovery appears to be on par with the first one. To date, about 15 large vertebrae, a few paddle bones and many bone fragments have been collected, but an extensive excavation is still in progress, so Ehret is uncertain how complete this skeleton is.

“We find a lot of the more common fossils here, but this is a macropredator that is not normally found in Alabama,” Ehret said. “It’s really interesting because it gives us a bigger picture of what was happening in Alabama at that time.”

The skeleton was also not found near water. Ehret said during the late Cretaceous period, temperatures were much warmer than they are today, resulting in higher sea levels. The specimen was found in a small quarry in rural Greene County, a region commonly called the “Black Belt.”

The “Black Belt” represents the late Cretaceous shoreline in the Gulf Coast. The sediments found in this region are classified as chalk, are composed of extinct microscopic organisms and are extremely nutrient rich, making them the perfect place for farming.

The discovery was made during the Museum’s Expedition 35, which was hosted by UA’s Alabama Museum of Natural History and led by Randy Mecredy, director of the Museum. The expedition is an annual summer program that is open to middle and high-school students.

In addition to Ehret, others involved in the excavation include students from the expedition, Dr. Takehito “Ike” Ikejiri with UA’s department of geological sciences, museum staff, Dr. Prescott Atkinson of the University of Alabama at Birmingham, the UA Museum’s Board of Regents and a few UA geology students.

The bones were initially excavated in place from the chalk in the quarry. Once they were able to determine the size and extent of the individual bones, those working the excavation could take them out of the ground and transport them back to the museum. Some pieces came back loose, while others were wrapped to prevent them from falling apart.

In the paleontology lab, the bones are now being unwrapped and prepared. Specimens are washed and scrubbed to remove loose sediments, and, for those that are still embedded in the chalk sediment, Ehret said they will use different tools to remove the sediment.

It will take several weeks to prepare the bones properly and then harden them to ensure they will not later fall apart. Once finished, the specimen will be displayed in UA’s Smith Hall.

“From a research standpoint, this is an important find. To have this many pieces, you can do an extensive comparative analysis,” Mecredy said. “But, it’s also having the ability to take high-school and middle-school students in the field where they find these things. It inspires them to pursue science-related fields.”

Scientists Cast Doubt On Theory of What Triggered Antarctic Glaciation

July 15th, 2013

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A team of U.S. and U.K. scientists has found geologic evidence that casts doubt on one of the conventional explanations for how Antarctica’s ice sheet began forming. Ian Dalziel, research professor at The University of Texas at Austin’s Institute for Geophysics and professor in the Jackson School of Geosciences, and his colleagues report the findings today in an online edition of the journal Geology.

The Antarctic Circumpolar Current (ACC), an ocean current flowing clockwise around the entire continent, insulates Antarctica from warmer ocean water to the north, helping maintain the ice sheet. For several decades, scientists have surmised that the onset of a complete ACC played a critical role in the initial glaciation of the continent about 34 million years ago.

Now, rock samples from the central Scotia Sea near Antarctica reveal the remnants of a now-submerged volcanic arc that formed sometime before 28 million years ago and might have blocked the formation of the ACC until less than 12 million years ago. Hence, the onset of the ACC may not be related to the initial glaciation of Antarctica, but rather to the subsequent well-documented descent of the planet into a much colder “icehouse” glacial state.

“If you had sailed into the Scotia Sea 25 million years ago, you would have seen a scattering of volcanoes rising above the water,” says Dalziel. “They would have looked similar to the modern volcanic arc to the east, the South Sandwich Islands.”

Using multibeam sonar to map seafloor bathymetry, which is analogous to mapping the topography of the land surface, the team identified seafloor rises in the central Scotia Sea. They dredged the seafloor at various points on the rises and discovered volcanic rocks and sediments created from the weathering of volcanic rocks. These samples are distinct from normal ocean floor lavas and geochemically identical to the presently active South Sandwich Islands volcanic arc to the east of the Scotia Sea that today forms a barrier to the ACC, diverting it northward.

This is a physiographic map of the present-day Scotia Sea, Drake Passage and adjacent land masses. The white arrows show the present path of the several branches of the deep Antarctic Circumpolar Current (ACC) centered on its core. The area of study in the central Scotia Sea (CSS) is shown by the black box to the south of South Georgia island (SG). The volcano symbols mark the active South Sandwich volcanic arc (SSA). (WSS = western Scotia Sea; ESS = eastern Scotia Sea) (Credit: University of Texas at Austin)

Using a technique known as argon isotopic dating, the researchers found that the samples range in age from about 28 million years to about 12 million years. The team interpreted these results as evidence that an ancient volcanic arc, referred to as the ancestral South Sandwich arc (ASSA), was active in the region during that time and probably much earlier. Because the samples were taken from the current seafloor surface and volcanic material accumulates from the bottom up, the researchers infer that much older volcanic rock lies beneath.

Combined with models of how the seafloor sinks vertically with the passage of time, the team posits that the ASSA originally rose above sea level and would have blocked deep ocean currents such as the ACC.

Two other lines of evidence support the notion that the ACC didn’t begin until less than 12 million years ago. First, the northern Antarctic Peninsula and southern Patagonia didn’t become glaciated until less than approximately 12 million years ago. And second, certain species of microscopic creatures called dinoflagellates that thrive in cold polar water began appearing in sediments off southwestern Africa around 11.1 million years ago, suggesting colder water began reaching that part of the Atlantic Ocean.

Earth’s Core Affects Length of Day

July 14th, 2013

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Researchers studied the variations and fluctuations in the length of day over a one to 10 year period between 1962 and 2012

Research at the University of Liverpool has found that variations in the length of day over periods of between one and 10 years are caused by processes in Earth’s core.

Earth rotates once per day, but the length of this day varies. A year, 300million years ago, lasted about 450 days and a day would last about 21 hours.

Length of day increases

As a result of the slowing down of Earth’s rotation the length of day has increased.

The rotation of Earth on its axis, however, is affected by a number of other factors — for example, the force of the wind against mountain ranges changes the length of the day by plus or minus a millisecond over a period of a year.

Professor Richard Holme, from the School of Environmental Sciences, studied the variations and fluctuations in the length of day over a one to 10 year period between 1962 and 2012. The study took account of the effects on Earth’s rotation of atmospheric and oceanic processes to produce a model of the variations in the length of day on time scales longer than a year.

The form of core motions giving rise to variations in Earth’s length of day. (Credit: Image courtesy of University of Liverpool)

Professor Holme said: “The model shows well-known variations on decadal time scales, but importantly resolves changes over periods between one and 10 years.

“Previously these changes were poorly characterised; the study shows they can be explained by just two key signals, a steady 5.9 year oscillation and episodic jumps which occur at the same time as abrupt changes in the Earth’s magnetic field, generated in the Earth’s core.

He added: “This study changes fundamentally our understanding of short-period dynamics of the Earth’s fluid core. It leads us to conclude that the Earth’s lower mantle, which sits above the Earth’s outer core, is a poor conductor of electricity giving us new insight into the chemistry and mineralogy of the Earth’s deep interior.”

The research was conducted in partnership with the Université Paris Diderot and is published in Nature.

Recent Earthquake Activity Is Not Unusual, Scientists Say

July 13th, 2013

Riffin

China’s tragic magnitude 6.9 earthquake on April 13 and the recent devastating earthquakes in Haiti, Chile, Mexico, and elsewhere have many wondering if this earthquake activity is unusual.

Scientists say 2010 is not showing signs of unusually high earthquake activity. Since 1900, an average of 16 magnitude 7 or greater earthquakes — the size that seismologists define as major — have occurred worldwide each year. Some years have had as few as 6, as in 1986 and 1989, while 1943 had 32, with considerable variability from year to year.

With six major earthquakes striking in the first four months of this year, 2010 is well within the normal range. Furthermore, from April 15, 2009, to April 14, 2010, there have been 18 major earthquakes, a number also well within the expected variation.

“While the number of earthquakes is within the normal range, this does not diminish the fact that there has been extreme devastation and loss of life in heavily populated areas,” said USGS Associate Coordinator for Earthquake Hazards Dr. Michael Blanpied.

What will happen next? Aftershocks will continue in the regions around each of this year’s major earthquakes sites. It is unlikely that any of these aftershocks will be larger than the earthquakes experienced so far, but structures damaged in the previous events could be further damaged and should be treated with caution. Beyond the ongoing aftershock sequences, earthquakes in recent months have not raised the likelihood of future major earthquakes; that likelihood has not decreased, either. Large earthquakes will continue to occur just as they have in the past.

Though the recent earthquakes are not unusual, they are a stark reminder that earthquakes can produce disasters when they strike populated areas — especially areas where the buildings have not been designed to withstand strong shaking. What can you do to prepare? Scientists cannot predict the timing of specific earthquakes. However, families and communities can improve their safety and reduce their losses by taking actions to make their homes, places of work, schools and businesses as earthquake-safe as possible.

Insect fossil Sheds Light On Climate Change

July 12th, 2013

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Simon Fraser University biologists have discovered a new, extinct family of insects that will help scientists better understand how some animals responded to global climate change and the evolution of communities.

“The Eocene Apex of Panorpoid Family Diversity,” a paper by SFU’s Bruce Archibald and Rolf Mathewes, plus David Greenwood from Brandon University, was recently published in the Journal of Paleontology.

Fossil of a newly discovered family of extinct scorpionflies from McAbee, B.C. (Credit: Image courtesy of Simon Fraser University)

The researchers named the new family the Eorpidae, after the Eocene Epoch, the age when these insects lived some 50 million years ago. The fossils were found in British Columbia and Washington state, most prominently at the McAbee Fossil Beds near Cache Creek, B.C.

This new family raises questions about its extinction. Insect families have steadily accumulated since before the Eocene, with few, scattered losses — apart from the distinct exception of a cluster of family extinctions within a group of scorpionflies that includes the Eorpidae.

“The Eorpidae was part of a cluster of six closely related families in the Eocene, but today this group is reduced to two. Why were these different?” says Archibald. “We believe the answer may lay in a combination of two large-scale challenges that would have hit them hard: the evolutionary diversification of a strong competitive group and global climate change.”

In a major evolutionary diversification, ants evolved from a small group to become major ecological players in the Eocene, now competing with these scorpionflies for the same food resource in a whole new, efficient manner.

Global climates were much warmer 50 million years ago, associated with increased atmospheric carbon, a relationship that scientists see today. Along with this, winters were mild, even in the cool, higher elevations where these insects lived. Average temperatures there were similar to modern Vancouver, but with few — if any — frost days.

When climates outside of the tropics later cooled, temperature seasonality also widened, forming the modern pattern of hot summers and freezing winters. Plant and animal groups that inhabited Eocene uplands either had to evolve tolerance for colder winters, migrate to the hot tropics and adapt to that climate, or go extinct.

“These scorpionfly families appear to have retained their need to inhabit cooler climates, but to persist there, they would need to evolve toleration for cold winters, a feat that only the two surviving families may have accomplished,” Archibald explains. “Understanding the evolutionary history of these insects adds another piece to the puzzle of how animal communities change as climate does — but in this case, when an interval of global warming ends.”

How Early Earth Kept Warm Enough to Support Life

July 11th, 2013

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Solving the “faint young sun paradox” — explaining how early Earth was warm and habitable for life beginning more than 3 billion years ago even though the sun was 20 percent dimmer than today — may not be as difficult as believed, says a new University of Colorado Boulder study.

In fact, two CU-Boulder researchers say all that may have been required to sustain liquid water and primitive life on Earth during the Archean eon 2.8 billion years ago were reasonable atmospheric carbon dioxide amounts believed to be present at the time and perhaps a dash of methane. The key to the solution was the use of sophisticated three-dimensional climate models that were run for thousands of hours on CU’s Janus supercomputer, rather than crude, one-dimensional models used by almost all scientists attempting to solve the paradox, said doctoral student Eric Wolf, lead study author.

An artist’s conception of the Earth during the late Archean, 2.8 billion years ago. Weak solar radiation requires the Earth have increased greenhouse gas amounts to remain warm. CU-Boulder doctoral student Eric Wolf Wolf and CU-Boulder Professor Brian Toon use a three-dimensional climate model to show that the late Archean may have maintained large areas of liquid surface water despite a relatively weak greenhouse. With carbon dioxide levels within constraints deduced from ancient soils, the late Archean may have had large polar ice caps but lower latitudes would have remained temperate and thus hospitable to life. The addition of methane allows the late Archean to warmed to present day mean surface temperatures. (Credit: Charlie Meeks)

“It’s really not that hard in a three-dimensional climate model to get average surface temperatures during the Archean that are in fact moderate,” said Wolf, a doctoral student in CU-Boulder’s atmospheric and oceanic sciences department. “Our models indicate the Archean climate may have been similar to our present climate, perhaps a little cooler. Even if Earth was sliding in and out of glacial periods back then, there still would have been a large amount of liquid water in equatorial regions, just like today.”

Evolutionary biologists believe life arose on Earth as simple cells roughly 3.5 billion years ago, about a billion years after the planet is thought to have formed. Scientists have speculated the first life may have evolved in shallow tide pools, freshwater ponds, freshwater or deep-sea hydrothermal vents, or even arrived on objects from space.

A cover article by Wolf and CU-Boulder Professor Brian Toon on the topic appears in the July issue of Astrobiology.

Scientists have been trying to solve the faint young sun paradox since 1972, when Cornell University scientist Carl Sagan — Toon’s doctoral adviser at the time — and colleague George Mullen broached the subject. Since then there have been many studies using 1-D climate models to try to solve the faint young sun paradox — with results ranging from a hot, tropical Earth to a “snowball Earth” with runaway glaciation — none of which have conclusively resolved the problem.

“In our opinion, the one-dimensional models of early Earth created by scientists to solve this paradox are too simple — they are essentially taking the early Earth and reducing it to a single column atmospheric profile,” said Toon. “One-dimensional models are simply too crude to give an accurate picture.”

Wolf and Toon used a general circulation model known as the Community Atmospheric Model version 3.0 developed by the National Center for Atmospheric Research in Boulder and which contains 3-D atmosphere, ocean, land, cloud and sea ice components. The two researchers also “tuned up” the model with a sophisticated radiative transfer component that allowed for the absorption, emission and scattering of solar energy and an accurate calculation of the greenhouse effect for the unusual atmosphere of early Earth, where there was no oxygen and no ozone, but lots of CO₂ and possibly methane.

The simplest solution to the faint sun paradox, which duplicates Earth’s present climate, involves maintaining roughly 20,000 parts per million of the greenhouse gas CO₂ and 1,000 ppm of methane in the ancient atmosphere some 2.8 billion years ago, said Wolf. While that may seem like a lot compared to today’s 400 ppm of CO₂ in the atmosphere, geological studies of ancient soil samples support the idea that CO₂ likely could have been that high during that time period. Methane is considered to be at least 20 times more powerful as a greenhouse gas than CO₂ and could have played a significant role in warming the early Earth as well, said the CU researchers.

There are other reasons to believe that CO₂ was much higher in the Archean, said Toon, who along with Wolf is associated with CU’s Laboratory for Atmospheric and Space Physics. The continental area of Earth was smaller back then so there was less weathering of the land and a lower release of minerals to the oceans. As a result there was a smaller conversion of CO₂ to limestone in the ocean. Likewise, there were no “rooted” land plants in the Archean, which could have accelerated the weathering of the soils and indirectly lowered the atmospheric abundance of CO₂, Toon said.

Another solution to achieving a habitable but slightly cooler climate under the faint sun conditions is for the Archean atmosphere to have contained roughly 15,000 to 20,000 ppm of CO₂ and no methane, said Wolf. “Our results indicate that a weak version of the faint young sun paradox, requiring only that some portion of the planet’s surface maintain liquid water, may be resolved with moderate greenhouse gas inventories,” the authors wrote in Astrobiology.

“Even if half of Earth’s surface was below freezing back in the Archean and half was above freezing, it still would have constituted a habitable planet since at least 50 percent of the ocean would have remained open,” said Wolf. “Most scientists have not considered that there might have been a middle ground for the climate of the Archean.

“The leap from one-dimensional to three-dimensional models is an important step,” said Wolf. “Clouds and sea ice are critical factors in determining climate, but the one-dimensional models completely ignore them.”

Has the faint young sun paradox finally been solved? “I don’t want to be presumptuous here,” said Wolf. “But we show that the paradox is definitely not as challenging as was believed over the past 40 years. While we can’t say definitively what the atmosphere looked like back then without more geological evidence, it is certainly not a stretch at all with our model to get a warm early Earth that would have been hospitable to life.”

“The Janus supercomputer has been a tremendous addition to the campus, and this early Earth climate modeling project would have impossible without it,” said Toon. The researchers estimated the project required roughly 6,000 hours of supercomputer computation time, an effort equal to about 10 years on a home computer.

The study was funded by two NASA grants and by the National Science Foundation, which supports CU-Boulder’s Janus supercomputer used for the study.

The Origin of the Turtle Shell: Mystery Solved

July 10th, 2013

Riffin

A team of researchers from Japan has finally solved the riddle of the origin of the turtle shell.

By observing the development of different animal species and confirming their results with fossil analysis and genomic data, researchers from the RIKEN Center for Developmental Biology show that the shell on the turtle’s back derives only from its ancestors’ ribcage and not from a combination of internal and external bone structures as is often thought. Their study is published today in the journal Nature Communications.

Juvenile soft-shelled turtle swimming up to breathe the air. In most reptiles, birds and mammals, the rib cage movement aids breathing, but in the evolution towards turtles, the rib cage was transformed into the immovable shell covering the animal’s back. (Credit: Image courtesy of RIKEN)

The skeleton of vertebrates has evolved throughout history from two different structures, called the endo- and exoskeleton. In the human skeleton, the backbone and bones of the limbs evolved from the endoskeleton, whereas most of the skull elements derive from the exoskeleton. Fish scales and the alligator’s bony skin nodules are other examples of exoskeletons.

The origin of the shell on the turtle’s back, or carapace, was unclear until now because it comprises parts of obvious endoskeletal origin and others that look more like the exoskeleton of alligators and fish. The outer part of the turtle carapace was thought to have derived from exoskeletal bones, while the internal part has been shown to originate from ribs and vertebrae and to be connected to the internal skeleton of the animal. However, no direct evidence has been obtained to show that the bony structures developing outside the ribcage in turtles derived from the exoskeleton.

To investigate whether the turtle carapace evolved with any contribution from its ancestors’ exoskeleton, Dr. Tatsuya Hirasawa and his team carefully observed developing embryos of Chinese soft-shell turtles, chickens and alligators.

In their analysis, they compared the development of the turtle carapace, the chick’s ribs and the alligator’s bony skin nodules.

The researchers found that the major part of the turtle’s carapace is made from hypertrophied ribs and vertebrae and therefore derives solely from endoskeletal tissue.

This finding was confirmed by the observation of fossils of the ancient turtle Odontochelys and the ancient reptile Sinosaurosphargis, that both exhibit shells of endoskeletal origin. Odontochelys has a rigid shell instead of a flexible ribcage. And Sinosaurosphargis possesses an endoskeletal shell similar to the turtle’s under, and separate from, a layer of exoskeletal bones.

Taken together these results show that the turtle carapace has evolved independently from the exoskeleton. This scenario is also consistent with the recent phylogenetic analyses based on genomic data that have placed turtles in the same group as birds, crocodiles and marine reptiles like Sinosaurophargis, contradicting recent studies based solely on fossil record.

“Recently, genomic analyses had given us evidence that turtles evolved from reptiles closely related to alligators and dinosaurs, not from primitive reptiles as once thought. Our findings match the evolutionary history revealed by the genomic analyses, and we are about to unravel the mystery of when and how the turtle shell evolved,” explains Dr. Tatsuya Hirasawa who led the research.

“Our aim is to one day understand it as well as we understand the evolution of birds from dinosaurs,” he concludes.

The Evolution of Fins to Limbs in the Land Invasion Race

July 8th, 2013

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Why did animals with limbs win the race to invade land over those with fins? A new study comparing the forces acting on fins of mudskipper fish and on the forelimbs of tiger salamanders can now be used to analyze early fossils that spanned the water-to-land transition in tetrapod evolution, and further understand their capability to move on land.

Mudskipper fish and tiger salamanders have similar characteristics to early tetrapod ancestors. (Credit: Sandy Kawano)

Research conducted by Sandy Kawano and Richard Blob at Clemson University compared terrestrial locomotion in tiger salamanders and mudskipper fish, which have similar characteristics to early tetrapod ancestors.

The researchers filmed these organisms as they walked over a force platform which measures forces like a bathroom scale but separates them into 3 directions (upward, fore-aft, and side-to-side). They compared the forces experienced by the pectoral fins of the mudskipper fishes to the forelimbs and hind limbs of walking tiger salamanders. The results showed that that mudskippers’ pectoral fins experience more medial forces than the limbs of salamanders, and that the forelimbs could have a played a similar weight-bearing role as the hind limbs.

Sandy Kawano said: “The transition from fins to limbs marks the most dramatic change in orientation of the locomotor forces from contact with the ground. Using these data we can now evaluate the locomotor capabilities of numerous important fossil taxa that spanned the water-to-land transition in tetrapod evolution. We hypothesise that the medial orientation of the forces on pectoral fins would result in unreasonably high bone stresses in early amphibious fish with fins, which would explain why the evolutionary invasion of land by vertebrates was accomplished instead by tetrapods with limbs with digits.”