Oct 24, 2016

Preferentially Earth-sized planets with lots of water

Artist’s impression of Earth-sized planets orbiting a red dwarf star.
Computer simulations by astrophysicists at the University of Bern of the formation of planets orbiting in the habitable zone of low mass stars such as Proxima Centauri show that these planets are most likely to be roughly the size of Earth and to contain large amounts of water.

In August 2016, the announcement of the discovery of a terrestrial exoplanet orbiting in the habitable zone of Proxima Centauri stimulated the imagination of the experts and the general public. After all this star is the nearest star to our sun even though it is ten times less massive and 500 times less luminous. This discovery together with the one in May 2016 of a similar planet orbiting an even lower mass star (Trappist-1) convinced astronomers that such red dwarfs (as these low mass stars are called) might be hosts to a large population of Earth-like planets.

How could these objects look like? What could they be made of? Yann Alibert and Willy Benz at the Swiss NCCR PlanetS and the Center of Space and Habitability (CSH) at the University of Bern carried out the first computer simulations of the formation of the population of planets expected to orbit stars ten times less massive than the sun.

"Our models succeed in reproducing planets that are similar in terms of mass and period to the ones observed recently," Yann Alibert explains the result of the study that has been accepted for publication as a Letter in the journal "Astronomy and Astrophysics." "Interestingly, we find that planets in close-in orbits around these type of stars are of small sizes. Typically, they range between 0.5 and 1.5 Earth radii with a peak at about 1.0 Earth radius. Future discoveries will tell if we are correct!" the researcher adds.

Ice at the bottom of the global ocean

In addition, the astrophysicists determined the water content of the planets orbiting their small host star in the habitable zone. They found that considering all the cases, around 90% of the planets are harbouring more than 10% of water. For comparison: Earth has a fraction of water of only about 0,02%. So most of these alien planets are literally water worlds in comparison! The situation could be even more extreme if the protoplanetary disks in which these planets form live longer than assumed in the models. In any case, these planets would be covered by very deep oceans at the bottom of which, owing to the huge pressure, water would be in form of ice.

Water is required for life as we know it. So could these planets be habitable indeed? "While liquid water is generally thought to be an essential ingredient, too much of a good thing may be bad," says Willy Benz. In previous studies the scientists in Bern showed that too much water may prevent the regulation of the surface temperature and destabilizes the climate. "But this is the case for Earth, here we deal with considerably more exotic planets which might be subjected to a much harsher radiation environment, and/or be in synchronous " he adds.

Following the growth of planetary embryos

To start their calculations, the scientists considered a series of a few hundreds to thousands of identical, low mass stars and around each of them a protoplanetary disk of dust and gas. Planets are formed by accretion of this material. Alibert and Benz assumed that at the beginning, in each disk there were 10 planetary embryos with an initial mass equal to the mass of the Moon. In a few day's computer time for each system the model calculated how these randomly located embryos grew and migrated. What kind of planets are formed depends on the structure and evolution of the protoplanetary disks.

Read more at Science Daily

The universe is expanding at an accelerating rate, or is it?

The universe may not be expanding at an accelerating rate, as previously thought, but rather, at a constant rate, suggests new research.
Five years ago, the Nobel Prize in Physics was awarded to three astronomers for their discovery, in the late 1990s, that the universe is expanding at an accelerating pace.

Their conclusions were based on analysis of Type Ia supernovae -- the spectacular thermonuclear explosion of dying stars -- picked up by the Hubble space telescope and large ground-based telescopes. It led to the widespread acceptance of the idea that the universe is dominated by a mysterious substance named 'dark energy' that drives this accelerating expansion.

Now, a team of scientists led by Professor Subir Sarkar of Oxford University's Department of Physics has cast doubt on this standard cosmological concept. Making use of a vastly increased data set -- a catalogue of 740 Type Ia supernovae, more than ten times the original sample size -- the researchers have found that the evidence for acceleration may be flimsier than previously thought, with the data being consistent with a constant rate of expansion.

The study is published in the Nature journal Scientific Reports.

Professor Sarkar, who also holds a position at the Niels Bohr Institute in Copenhagen, said: 'The discovery of the accelerating expansion of the universe won the Nobel Prize, the Gruber Cosmology Prize, and the Breakthrough Prize in Fundamental Physics. It led to the widespread acceptance of the idea that the universe is dominated by "dark energy" that behaves like a cosmological constant -- this is now the "standard model" of cosmology.

'However, there now exists a much bigger database of supernovae on which to perform rigorous and detailed statistical analyses. We analysed the latest catalogue of 740 Type Ia supernovae -- over ten times bigger than the original samples on which the discovery claim was based -- and found that the evidence for accelerated expansion is, at most, what physicists call "3 sigma." This is far short of the "5 sigma" standard required to claim a discovery of fundamental significance.

'An analogous example in this context would be the recent suggestion for a new particle weighing 750 GeV based on data from the Large Hadron Collider at CERN. It initially had even higher significance -- 3.9 and 3.4 sigma in December last year -- and stimulated over 500 theoretical papers. However, it was announced in August that new data shows that the significance has dropped to less than 1 sigma. It was just a statistical fluctuation, and there is no such particle.'

There is other data available that appears to support the idea of an accelerating universe, such as information on the cosmic microwave background -- the faint afterglow of the Big Bang -- from the Planck satellite. However, Professor Sarkar said: 'All of these tests are indirect, carried out in the framework of an assumed model, and the cosmic microwave background is not directly affected by dark energy. Actually, there is indeed a subtle effect, the late-integrated Sachs-Wolfe effect, but this has not been convincingly detected.

'So it is quite possible that we are being misled and that the apparent manifestation of dark energy is a consequence of analysing the data in an oversimplified theoretical model -- one that was in fact constructed in the 1930s, long before there was any real data. A more sophisticated theoretical framework accounting for the observation that the universe is not exactly homogeneous and that its matter content may not behave as an ideal gas -- two key assumptions of standard cosmology -- may well be able to account for all observations without requiring dark energy. Indeed, vacuum energy is something of which we have absolutely no understanding in fundamental theory.'

Read more at Science Daily

How snakes lost a blueprint for making limbs

This image depicts mouse embryos with the ZRS from cobra or python inserted into their genomes, replacing the normal gene regulator. Their truncated limb development is visible in the comparative bone scans.
Snakes lost their limbs over 100 million years ago, but scientists have struggled to identify the genetic changes involved. A Cell paper publishing October 20 sheds some light on the process, describing a stretch of DNA involved in limb formation that is mutated in snakes. When researchers inserted the snake DNA into mice, the animals developed truncated limbs, suggesting that a critical stretch of DNA lost its ability to support limb growth during snake evolution.

"This is one of many components of the DNA instructions needed for making limbs in humans and, essentially, all other legged vertebrates. In snakes, it's broken," says Axel Visel, a geneticist at the Lawrence Berkeley National Laboratory and senior author on the paper. "It's probably one of several evolutionary steps that occurred in snakes, which, unlike most mammals and reptiles, can no longer form limbs."

Today's serpents have undergone one of the most dramatic body plan changes in the evolution of vertebrates. To study the molecular roots of this adaptation, Visel and his colleagues started looking at published snake genomes, including the genomes from basal snakes such as boa and python, which have vestigial legs -- tiny leg bones buried in their muscles -- and advanced snakes, such as viper and cobra, which that have lost all limb structures. Within these genomes, they focused specifically on a gene called Sonic hedgehog, or Shh, involved in many developmental processes -- including limb formation. The researchers delved further into one of the Shh gene regulators, a stretch of DNA called ZRS (the Zone of Polarizing Activity Regulatory Sequence) that was present but had diverged in snakes.

To determine the consequences of these mutations, the researchers used CRISPR, a genome-editing method, to insert the ZRS from various other vertebrates into mice, replacing the mouse regulator. With the ZRS of other mammals, such as humans, the mice developed normal limbs. Even when they inserted the ZRS from fish, whose fins are structurally very different from limbs, the mice developed normal limbs. However, when the researchers replaced the mouse ZRS with the python or cobra version, the mice went on to develop severely truncated forelimbs and hindlimbs.

"Using these new genomic tools, we can begin to explore how different evolutionary versions of the same enhancer affect limb development and actually see what happens," says Visel. "We used to be mostly staring at sequences and speculating about molecular evolution, but now, we can really take these studies to the next level."

To identify the mutations in the snakes' ZRS that were responsible for its inactivation during snake evolution, the researchers took a closer look at the evolutionary history of individual sequence changes. By comparing the genomes of snakes and other vertebrates, they identified one particularly suspicious 17 base-pair deletion that only occurred in snakes; this deletion removed a stretch of the ZRS that has a key role in regulating the Shh gene in legged animals.

The research team turned back the evolutionary clock, restoring the missing 17 base pairs in an artificially created hybrid version of the python ZRS, and tested the edited DNA in mice. Those that carried this evolutionarily "resurrected" ZRS in their genome, replacing their normal regulator, developed normal legs. However, Visel cautions that the evolutionary events were probably more complex than just the one deletion: "There's likely some redundancy built into in the mouse ZRS. A few of the other mutations in the snake ZRS probably also played a role in its loss of function during evolution."

Read more at Science Daily

Ancient human history more complex than previously thought, researchers say

Primitive people (stock image). New research results suggest that throughout Eurasia, ancient populations interbred less than previously believed, and that -- contrary to previous findings -- the level of mixing with Neanderthals did not differ significantly between Europe and East Asia.
Relationships between the ancestors of modern humans and other archaic populations such as Neanderthals and Denisovans were likely more complex than previously thought, involving interbreeding within and outside Africa, according to a new estimator developed by geneticists. Findings were reported at the American Society of Human Genetics (ASHG) 2016 Annual Meeting in Vancouver, B.C.

In recent years, genetics has led to the revision of many assumptions about archaic populations, explained Ryan J. Bohlender, PhD, a postdoctoral researcher at the University of Texas MD Anderson Cancer Center and first author on the research. For example, the 2010 release of the Neanderthal genome led to the discovery that Neanderthals and the ancestors of modern Europeans interbred. A few years later, scientists discovered the existence of Denisovans, a population known of only through genetics, through a fossilized sample of DNA.

"My colleagues and I set out to find out what we might share with these ancient populations and how our histories interacted," Dr. Bohlender said. They developed an estimation tool to model these interactions based on parameters such as current estimates of population size and dates when populations separated -- how long ago they stopped interbreeding -- and look for inconsistencies with information known from genetic studies about the overlap between the modern human genome and those of ancient populations. Compared to previous estimators, this one made increased use of genetic data to cut down on statistical bias. The researchers then allowed estimates of population size and separation dates to vary in a series of simulations, in order to find out if adjusting these parameters better fit the genetic data.

"Using this process, we found that the population in Africa was likely about 50 percent larger than previously thought. We also found that an archaic-modern human separation date of 440,000 years ago was the best fit, suggesting that Neanderthals diverged from our lineage 100,000 years more recently than we thought," Dr. Bohlender said. "We got the same separation date using data from multiple modern human populations, which is a good sign."

In addition, their results suggest that throughout Eurasia, ancient populations interbred less than previously believed, and that -- contrary to previous findings -- the level of mixing with Neanderthals did not differ significantly between Europe and East Asia.

The findings bring up many new questions, including to what extent the new estimator can be trusted, why it produces results that differ from prevailing estimates, and how to reconcile these differences.

"Overall, our findings confirm the human family tree is more complicated than we think it is," Dr. Bohlender said. "For example, other archaic populations are likely to have existed, like the Denisovans, who we didn't know about except through genetics." They plan to try out simulations with multiple other populations, to see if this adds some clarity to the results.

Dr. Bohlender also believes that more detailed studies of African populations may shed some light. "Africans have been underrepresented in genetics research -- they're not as well studied as European and Asian populations, yet they are more diverse genetically than any other group," he said.

From Science Daily

Oct 22, 2016

Climate change impairs survival instincts of fish and can make them swim towards predators

Carbon dioxide levels are predicted to be 2.5 times higher in the oceans by the end of this century.
Climate change is disrupting the sensory systems of fish and can even make them swim towards predators, instead of away from them, a paper by marine biologists at the University of Exeter says.

Research into the impact of rising CO2 has shown it can disrupt the senses of fish including their smell, hearing and vision.

High CO2 levels can impair the way they behave, including making them swim towards predator smells instead of away and even ignoring the sounds that normally deter them from risky habitats.

According to a paper published in the journal Global Change Biology by Dr Robert Ellis and Dr Rod Wilson, climate-change marine biologists at Exeter University, these abnormal behaviours have been linked to the effect of CO2 on how the brain processes signals from sensory organs.

CO2 levels are predicted to be 2.5 times higher in the oceans by the end of this century.

The report's authors Dr Robert Ellis and Dr Rod Wilson believe that fish farms, may be the key to establishing the long-term impact of CO2 on marine life.

In their paper, Lessons from two high CO2 worlds: future oceans and intensive aquaculture, Dr. Ellis and Dr. Wilson, alongside a colleague from Chile (Dr. Urbina), show that farmed fish often live in CO2 conditions 10 times higher than their wild cousins.

The scientists believe that further study of farmed fish -- which already provides as much seafood for human consumption as that caught in the wild -- may be crucial for understanding how aquatic species will evolve to climate change.

The captive fish farm populations living in high CO2 levels already amount to "a giant long-term laboratory experiment."

"Aquaculture may provide an 'accidental' long-term experiment that can help climate-change predictions," said Dr. Ellis. "There is the enticing possibility that fish and shellfish previously grown in high CO2 aquaculture conditions over multiple generations can offer valuable insights regarding the potential for aquatic animals in the wild to adapt to the predicted further increases in CO2."

The aquaculture industry may also benefit from what the climate change scientists study too. The abnormal behaviour seen in wild fish may not matter in farmed fish, as they are provided with abundant food and shelter and they have no predators to avoid. But while extremely high CO2 can reduce digestion efficiency in cod, recent research suggests that relatively small increases in CO2 may actually act as a growth stimulant in some fish.

Read more at Science Daily

New evolutionary finding: Species take different genetic paths to reach same trait

Jay Storz (left), Susan J. Rosowski professor of biological sciences, and Chandrasekhar Natarajan, research assistant professor in biological sciences.
Biologists have been contemplating evolutionary change since Charles Darwin first explained it.

Using modern molecular tools and fieldwork, University of Nebraska-Lincoln biologist Jay Storz and colleagues have demonstrated for the first time that different species can take different genetic paths to develop the same trait. The team's findings appear in the Oct. 21 issue of the journal Science.

"There's this really long-standing question in evolutionary genetics about the predictability of genetic change," said Storz, Susan J. Rosowski professor of biological sciences.

In other words, did species with a common, beneficial trait undergo the same genetic changes to evolve that trait? Or did the trait develop through different, and therefore unpredictable, genetic paths?

It turns out that natural selection, a primary evolutionary process, can dependably produce similar, beneficial traits in different species. But at the molecular level, the evolutionary changes tend to be highly idiosyncratic, and are therefore far less predictable.

To find that out, Storz turned to birds living in South America's Andes Mountains. Comparing high-altitude bird species with their lowland counterparts, his team determined that the high-altitude birds had evolved red blood cells with hemoglobin proteins that more readily bind oxygen molecules. This trait benefits species living in low-oxygen settings, such as the mountains.

Storz and his team tested the hemoglobin proteins from numerous high-altitude bird species and identified which differences, or mutations, in the proteins' makeup were responsible for the high-altitude trait. In most cases, the change in protein function among the different species was caused by different mutations.

"What this indicates is that there are many possible mutations that can all produce the same phenotypic effect (trait)," Storz said. "We can't predict which particular mutations are responsible for these changes." One possible reason for this variability is that during evolution, the hemoglobins of different species have each accumulated their own unique set of mutations. Given these distinct genetic backgrounds, a mutation that produces a beneficial effect in one species may produce a detrimental effect in a different species.

To test this theory, Storz's team used genetic engineering tools to reconstruct and resurrect the hemoglobin proteins of several ancestral bird species, including the ancestor common to all birds, which existed more than 100 million years ago. Engineering the high-altitude hemoglobin mutations into the ancient bird proteins resulted in vastly different effects than in contemporary birds.

As evolution advances through time, different mutations accumulate in distinct species and settings. Natural selection applies similar pressures for species to adapt as they move to higher altitudes, for example, but the adaptation must take different genetic paths to get there.

Read more at Science Daily

Oct 21, 2016

Earliest evidence in fossil record for right-handedness

David Frayer, KU professor emeritus of anthropology, is lead author on a recent study published in the Journal of Evolution that found striations on teeth of a Homo habilis fossil 1.8 million years old moved from left to right, indicating the earliest evidence in the fossil record for right-handedness. Researchers believe the marks came from using a tool to try to cut food being pulled from the mouth with the left hand.
Perhaps the bias against left-handers dates back much further than we thought.

By examining striations on teeth of a Homo habilis fossil, a new discovery led by a University of Kansas researcher has found the earliest evidence for right-handedness in the fossil record dating back 1.8 million years.

"We think that tells us something further about lateralization of the brain," said David Frayer, a KU professor emeritus of anthropology and the lead author of the study. "We already know that Homo habilis had brain lateralization and was more like us than like apes. This extends it to handedness, which is key."

The findings were published online this week in the Journal of Human Evolution. The researchers made the discovery after analyzing small cut marks, or labial striations, which are the lip side of the anterior teeth in an intact upper jaw fossil, known as OH-65, found in a stream channel of the Olduvai Gorge in Tanzania.

Frayer said among the network of deep striations found only on the lip face of the upper front teeth most cut marks veered from left down to the right. Analysis of the marks makes it likely they came from when OH-65 used a tool with its right hand to cut food it was holding in its mouth while pulling with the left hand. The scratches can be seen with the naked eye, but a microscope was used to determine their alignment and to quantify their angulation.

"Experimental work has shown these scratches were most likely produced when a stone tool was used to process material gripped between the anterior teeth and the tool occasionally struck the labial face leaving a permanent mark on the tooth's surface," Frayer said.

Based on the direction of the marks, it's evident the Homo habilis was right-handed. It's a sample of one, but because this is the first potential evidence of a dominant handed pre-Neanderthal, Frayer said, the study could lead to a search for the marks in other early Homo fossils.

"Handedness and language are controlled by different genetic systems, but there is a weak relationship between the two because both functions originate on the left side of the brain," he said. "One specimen does not make an incontrovertible case, but as more research is done and more discoveries are made, we predict that right-handedness, cortical reorganization and language capacity will be shown to be important components in the origin of our genus."

Multiple lines of research point to the likelihood that brain reorganization, the use of tools and use of a dominant hand occurred early in the human lineage. Today, researchers estimate that 90 percent of humans are right-handed, and this differs from apes which are closer to a 50-50 ratio. Until now, no one looked for directionality of striations in the earliest specimens representing our evolutionary lineage.

Read more at Science Daily

Oldest known planet-forming disk discovered

An artist's conception of this unusual system.
A group of citizen scientists and professional astronomers, including Carnegie's Jonathan Gagné, joined forces to discover an unusual hunting ground for exoplanets. They found a star surrounded by the oldest known circumstellar disk -- a primordial ring of gas and dust that orbits around a young star and from which planets can form as the material collides and aggregates.

Led by Steven Silverberg of University of Oklahoma, the team described a newly identified red dwarf star with a warm circumstellar disk, of the kind associated with young planetary systems. Circumstellar disks around red dwarfs like this one are rare to begin with, but this star, called AWI0005x3s, appears to have sustained its disk for an exceptionally long time. The findings are published by The Astrophysical Journal Letters.

"Most disks of this kind fade away in less than 30 million years," said Silverberg. "This particular red dwarf is a candidate member of the Carina stellar association, which would make it around 45 million years old [like the rest of the stars in that group]. It's the oldest red dwarf system with a disk we've seen in one of these associations."

The discovery relied on citizen scientists from Disk Detective, a project led by NASA/GSFC's Dr. Marc Kuchner that's designed to find new circumstellar disks. At the project's website, DiskDetective.org, users make classifications by viewing ten-second videos of data from NASA surveys, including the Wide-field Infrared Survey Explorer mission (WISE) and Two-Micron All Sky Survey (2MASS) projects. Since the launch of the website in January 2014, roughly 30,000 citizen scientists have participated in this process, performing roughly 2 million classifications of celestial objects.

"Without the help of the citizen scientists examining these objects and finding the good ones, we might never have spotted this object," Kuchner said. "The WISE mission alone found 747 million [warm infrared] objects, of which we expect a few thousand to be circumstellar disks."

"Unraveling the mysteries of our universe, while contributing to the advancement of astronomy, is without a doubt a dream come true," says Hugo Durantini Luca from Argentina, one of eight citizen scientist co-authors.

Determining the age of a star can be tricky or impossible. But the Carina association, where this red dwarf was found, is a group of stars whose motions through the Galaxy indicate that they were all born at roughly the same time in the same stellar nursery.

Carnegie's Gagné devised a test that showed this newly found red dwarf and its disk are likely part of the Carina association, which was key to revealing its surprising age.

"It is surprising to see a circumstellar disk around a star that may be 45 million years old, because we normally expect these disks to dissipate within a few million years," Gagné explained. "More observations will be needed to determine whether the star is really as old as we suspect, and if it turns out to be, it will certainly become a benchmark system to understand the lifetime of disks."

Knowing that this star and its disk are so old may help scientists understand why M dwarf disks appear to be so rare.

Read more at Science Daily

Early fossil fish from China shows where our jaws came from

Life reconstruction of Qilinyu along with Guiyu and Entelognathus in Silurian waters.
Where did our jaws come from? The question is more complicated than it seems, because not all jaws are the same. In a new article, published in Science, palaeontologists from China and Sweden trace our jaws back to the extinct placoderms, armoured prehistoric fish that lived over 400 million years ago.

Jaws are an iconic and defining feature, not only of our own anatomy but of all jawed vertebrates: not for nothing did Steven Spielberg use "Jaws" as the one-word title of his immortal shark epic.

Jaws first appear in the developing embryo as a cartilage bar similar to a gill arch. In a shark, this develops directly into the adult jaws, but in an embryo of a bony fish or a human being new bones appear on the outside of the cartilage. In our own skull, these bones -- the dentary, maxilla and premaxilla -- make up the entire jaws and carry our teeth.

It is universally accepted that the dentary, maxilla and premaxilla are a shared heritage of bony fishes and tetrapods: you will find these same bones in a crocodile or a cod. But what about further back? Only one other group of fishes, the extinct placoderms, have a similar set of jaw bones. But these bones, known as 'gnathal plates' and shown to spectacular effect in the giant placoderm Dunkleosteus where they are developed into blades like sheet-metal cutters, have always been regarded as unrelated to the dentary, maxilla and premaxilla. For one thing they are located slightly further inside the mouth, and in any case the general opinion has been that placoderms and bony fishes are only very distantly related.

The picture began to change fundamentally in 2013 with the description of Entelognathus, a Silurian (423 million year old) fossil fish from Yunnan in China which combines a classic placoderm skeleton with presence of a dentary, maxilla and premaxilla. Together with the discovery of placoderm-like characteristics in some of the earliest bony fishes, this began to build a strong case for a close relationship between placoderms and bony fishes, accompanied by a substantial carry-over of placoderm characteristics into bony fishes (and hence ultimately to us). But what about those jaws, where did they come from?

This is where the new fossil, Qilinyu, comes in. Qilinyu, described this week in Science by palaeontologists from the Institute of Vertebrate Paleontology and Paleoanthropology (IVPP) in Beijing and Uppsala University in Sweden, comes from the same place and time period as Entelognathus, and also combines a placoderm skeleton with dentary, maxilla and premaxilla, though the two fishes otherwise look quite different and must have had different lifestyles. Looking at the jaw bones of Entelognathus and Qilinyu we can see that they, in both fishes, combine characters of the bony fish jaw bones (they contribute to the outer surface of the face and lower jaw) and placoderm gnathal plates (they have broad biting surfaces inside the mouth). Another thing becomes apparent as well: it has been argued that placoderm gnathal plates represent an inner jaw arcade, similar in position to the 'coronoid bones' of bony fishes, and if that were true we would expect to find gnathal plates just inside of the dentary, maxilla and premaxilla of Entelognathus and Qilinyu; but there is nothing there.

Read more at Science Daily

New Aussie Dinosaur Was Half a Basketball Court Long

A new species of giant long-necked dinosaur revealed today sheds light on the likely origin of Australian sauropods.

The creature was called Savannasaurus elliottorum after grazier David Elliott, chairman of the Australian Age of Dinosaurs Museum (AAOD) in Winton, Queensland, who first found the fossil bones in the area during a sheep muster in 2005.

While the discovery site was excavated in September of that year by a team from the AAOD and Queensland Museum, it has taken the decade since to remove the bones from the rocks in which they were encased.

Savannasaurus belonged to a branch of sauropods known as titanosaurs, the largest land animals ever to have lived, said Dr Stephen Poropat of the AAOD Museum, who is lead author of a paper describing the findings in today's Scientific Reports.

He said only about 20 to 25 per cent of Savannasaurus' skeleton had been recovered with most of the torso, front limbs and pelvis intact.

"Because they are very large animals it would take a fair bit of sediment to bury it before predators come along," Dr Poropat said.

He said a tooth of a carnivorous dinosaur had been found at the fossil site, which suggested there had been some scavenging on the remains.

Dr Poropat said Savannasaurus would have been a medium-sized titanosaur about half the length of Diplodocus, measuring between 12 to 15 meters in length, with a long neck and relatively short tail.

However, he said its most distinctive feature was its hip width, which measured up to 1.5 meters.

Dr Poropat and colleagues also described another dinosaur, Diamantinasaurus matildae, first discovered in 2009, whose skeleton includes the first sauropod skull found in Australia.

Savannsaurus and the new Diamantinasaurus specimen shed light on a debate over the origin of Australian titanosaurs.

Previous studies of Australia's megafauna have suggested they were most similar to dinosaurs from Laurasia — the ancient continental mass in the Northern Hemisphere.

But Dr Poropat said this had never really made sense given the two super continents of Gondwana and Laurasia were separated.

He said the new study showed Savannasaurus and Diamantinasaurus were in fact more closely related to species from South America.

"But as the South American fossil record has improved and the Australian fossil record continues to grow, we are getting a better understanding of how close our dinosaurs were to those from South America."

Dr Poropat said it appeared Savannasaurus came to Australia around 105 million years ago from South America.

He said it appeared as if these titanosaurs took advantage of the warmer global temperatures at the time to disperse from South America through Antarctica to Australia at a time when all three continents were connected.

Dr Adam Yates, senior curator of earth sciences at the Northern Territory Museum, said he believed the paper's findings were valid.

Titanosaurs in particular represented one of the "last grey areas" of understanding in the dinosaur story.

"They are abundant and found all over the world, but their remains are often very incomplete, and as a consequence our understanding of the interrelationship of different titanosaurs is quite puzzling and we don't have a good family tree worked out yet," he said.

Read more at Discovery News