The mystery of the role of people and climate in the fate of Australian megafauna might have been solved in a breakthrough study.
Pleistocene kangaroo was the largest and most heavily built kangaroo known [Credit: Flinders University]
'Megafauna', giant beasts that once roamed the continent -- including wombat-like creatures as big as cars, birds more than two metres tall, and lizards more than seven metres long -- became extinct about 42,000 years ago. But the role of people in their demise has been hotly debated for decades.
For the first time, the research suggests a combination of climate change and the impact of people sealed the fate of megafauna, at least in south-eastern Australia. And that distribution of freshwater -- a precious commodity for animals and people alike as the climate warmed -- can explain regional differences in the timing at which megafauna died out.
The new study, led by a team of researchers from the ARC Centre of Excellence for Australian Biodiversity and Heritage (CABAH), analysed fossil data, climate reconstructions, and archaeological information describing patterns in human migration across south-eastern Australia.
The team developed and applied sophisticated mathematical models to test scenarios to explain regional variation in the periods during which people and megafauna coexisted.
"There has been much debate among scientists about what conditions led to this extinction event," said lead author Dr Frederik Saltre, Research Fellow and Coordinator of the Global Ecology Lab at Flinders University.
"Resolving this question is important because it is one of the oldest such extinction events anywhere after modern human beings evolved and left Africa", he added.
The findings, published in Nature Communications, are the result of analysis and complex modelling based on data including more than 10,000 fossils and archaeological records. Using high-quality fossil data and archaeological evidence of human activity, the researchers were able to map regional patterns of megafauna extinction.
They developed sophisticated models to test the impact of factors including climate, water availability, and human activity on localised patterns of megafauna extinction.
Credit: Flinders University
The extinction pattern could only be explained by the combination of people sharing the environment and the reduced of availability of freshwater due to climate change.
"The regional patterns in extinction are best explained by the hypothesis that people migrated across Australia, exploiting lakes and other sources of drinking water connecting the drier regions in between," said co-investigator Professor Corey Bradshaw of the Global Ecology Lab at Flinders University.
"It is plausible that megafauna species were attracted to the same freshwater sources as humans, thus increasing the chance of interactions."
The new insight that human pressure and climate change work together to trigger species extinction is a "stark warning" for the immediate future of the planet's biodiversity facing even stronger climate and habitat disruption, Dr Saltre concluded.
New fossils of an ancient legged snake, called Najash, shed light on the origin of the slithering reptiles.
Lifelike rendition of Najash [Credit: Raul O. Gomez, Universidad de Buenos Aires]
The fossil discoveries published in Science Advances have revealed they possessed hind legs during the first 70 million years of their evolution. They also provide details about how the flexible skull of snakes evolved from their lizard ancestors.
The evolution of the snake body has captivated researchers for a long time - representing one of the most dramatic examples of the vertebrate body's ability to adapt - but a limited fossil record has obscured our understanding of their early evolution until now.
Dr Alessandro Palci, from Flinders University, was part of the international research team that performed high-resolution (CT) scanning and light microscopy of the preserved skulls of Najash to reveal substantial new anatomical data on the early evolution of snakes.
Najash specimens from LBPA [Credit: Garberoglio et al. 2019]
"Snakes are famously legless, but then so are many lizards. What truly sets snakes apart is their highly mobile skull, which allows them to swallow large prey items. For a long time we have been lacking detailed information about the transition from the relatively rigid skull of a lizard to the super flexible skull of snakes".
"Najash has the most complete, three-dimensionally preserved skull of any ancient snake, and this is providing an amazing amount of new information on how the head of snakes evolved. It has some, but not all of the flexible joints found in the skull of modern snakes. Its middle ear is intermediate between that of lizards and living snakes, and unlike all living snakes it retains a well-developed cheekbone, which again is reminiscent of that of lizards."
Flinders University and South Australian Museum researcher Professor Mike Lee, was also part of the study, and adds "Najash shows how snakes evolved from lizards in incremental evolutionary steps, just like Darwin predicted."
CT scan reconstructions of the articulated skull of Najash [Credit: Garberoglio et al. 2019]
The new snake family tree also reveals that snakes possessed small but perfectly formed hind legs for the first 70 million years of their evolution.
"These primitive snakes with little legs weren't just a transient evolutionary stage on the way to something better. Rather, they had a highly successful body plan that persisted across many millions of years, and diversified into a range of terrestrial, burowing and aquatic niches," says Professor Lee.
As any geologist worth his or her salt will tell you, there are rocks, and then there are rocks. Next July, NASA and the European Space Agency (ESA) are launching rovers to Mars that will search for signs of past microbial life, and to find them, the scientists with NASA's Mars 2020 mission and ESA's ExoMars will need to examine different kinds of rocks that lend compelling insights into the environment in which they were made—all from 100 million miles away.
Scientists from NASA's Mars 2020 and ESA's ExoMars projects study stromatolites, the oldest confirmed fossilized lifeforms on Earth, in the Pilbara region of North West Australia. The image was taken on Aug. 19, 2019 [Credit: NASA/JPL-Caltech]
"While we expect to find many significant rocks during both Mars 2020 and ExoMars missions, we also have to leave open the possibility we could find one or more very special rocks,the kind whose discovery would not only speak volumes about the history of Mars but contribute significantly to the discussion of life elsewhere in the universe," said Ken Farley, Mars 2020 project scientist at Caltech in Pasadena.
Guided by Martin Van Kranendonk, director of the Australian Centre for Astrobiology at the University of New South Wales, members of the two missions' science teams went on an expedition to northwestern Australia's Pilbara region to analyze, discuss and debate stromatolites—structures preserved in rock that formed in water on early Earth and contain a fossilized record of ancient microbial life. Among the science teams' stops: a stromatolite cluster in a grouping of rock called the Dresser Formation that contains some of the oldest known fossilized records of life on our world.
"Some 3.48 billion years ago, this area was home to a caldera, or collapsed volcano, filled with hot, bubbling seawater," said Van Kranendonk. "At the same time, this location was also home to structures called microbial mats—visible to the naked eye but composed of microscopic organisms. Today you would know them as simple pond scum, but back then they were the most complex lifeforms on Earth."
Likely powered by photosynthesis, along with the heat and chemical energy in the caldera, these mats lived at the water's edge, secreting a mucous that would trap grains of sediment swirling around in the water. Over time, sheet after sheet of these microbes trapped sediment on top of previous layers. When the seawater receded and the pond scum dried up and disappeared millennia later, what remained was striking evidence of this co-evolution of geology and biology.
"A stromatolite is quite subtle to the untrained eye," said Van Kranendonk. "But once you know the details, you recognize that these wavy, wrinkly rocks have a structure different from that which can be explained by just geology."
Past Life on Mars?
Of course, the Outback isn't Mars, but what happened in the Dresser Formation a billion years ago and what happened on the Red Planet at roughly the same time share some eerie similarities.
Could Mars ever have supported life? In the Australian Outback, scientists from NASA's upcoming Mars 2020 mission
and their counterparts from the joint European-Russian ExoMars mission visited the oldest convincing evidence for
life on Earth to prepare for their own searches for signs of ancient life on Mars. The field lesson in astrobiology
in the Pilbara region is being applied in the near term by NASA, ESA and Roscosmos for mission planning,
and will also pay dividends when both rovers begin to send back science data and imagery
from the Red Planet [Credit: NASA/JPL-Caltech]
Between 3 billion and 4 billion years ago at the Mars 2020 landing site, Jezero Crater, a river flowed into a body of water the size of Lake Tahoe, depositing delta sediments packed with clay and carbonate minerals. The conditions were ideal for stromatolites to form on the shorelines, which is one key reason the rover team will be touching down there in February 2021. "It's hard to think of a better recipe for life to thrive—and for its record to be preserved—than the one we see at Jezero," said Ken Williford, deputy project scientist for Mars 2020 at JPL.
If stromatolites ever existed in Jezero or at Oxia Planum, the ExoMars landing site, the teams need to know what to look for, hence this trip to the Outback. But that's not the only reason they came.
"I organized this first joint Mars 2020-ExoMars science expedition so scientists from our two great missions could gain a new perspective on these one-of-a-kind stromatolites; a laboratory setting just can't provide the same context," said Mitch Schulte, Mars 2020 program scientist at NASA Headquarters in Washington. "That applies to the experience as a whole, too—the conversations, comparing of notes and planning for future exchanges that was done here in the Pilbara will go a long way to advance Mars science."
Two Missions, Two Rovers
While the two missions both seek to find evidence of past life, each is approaching the challenge in its own way. Touching down about a week after Mars 2020, the ExoMars rover, otherwise known as the Rosalind Franklin, carries a core drill that on two or more occasions will bore almost 7 feet (2 meters) into the Martian crust. The rover will analyze the samples onsite with a sophisticated suite of scientific instruments.
The coring mechanism on NASA's Mars 2020 rover drills shallower holes but is designed to collect more than 40 rock and soil core samples. There will be on-site analysis of rocks at the coring sites, and the samples themselves will be sealed in metal tubes that will ultimately be deposited by the rover at specific sites. Future missions could then retrieve those samples and return them to Earth for the sort of laboratory analysis that just isn't possible on Mars.
"These two Mars missions will be revolutionary because they are complementary," said Teresa Fornaro, a science team member for the Mars Organic Molecule Analyzer instrument aboard ExoMars. "Two different rovers with two different sets of instruments, exploring at the same time two different landing sites. Some of the capabilities of Mars 2020 in characterizing the surface environment could help guide ExoMars on where to drill. Conversely, knowledge of the alteration of possible organics as a function of depth by ExoMars could help Mars 2020 select the most interesting surface samples to collect for future return to Earth."
When the joint Mars 2020-ExoMars science Outback expedition concluded in late August, the science teams went their separate ways. But to those who honed their stromatolite-hunting skills in the Pilbara, the influence of the trip continues.
"What is happening working out here in the field is also happening in the halls of NASA and ESA," said Schulte. "Finding evidence of life on another world, if it ever existed, will require tenacity and a whole lot of brainpower. If there is a stromatolite in the range of the rovers, I think we have a good chance of finding it ... and we'll find it together. This trip will have helped with that."
The launch window for Mars 2020 opens on July 17, 2020. It will land at Mars' Jezero Crater on Feb. 18, 2021. The launch window for ExoMars opens July 25, 2020. It will land at Oxia Planum in March 2021.
A cache of 118 million-year-old fossilized dinosaur and bird feathers has been recovered from an ancient lake deposit that once lay beyond the southern polar circle.
Australian Feathered Polar Dinosaur [Credit: Peter Trusler]
Feathered dinosaur fossils are famous, but known from a handful of localities worldwide. Examples from the Southern Hemisphere are especially rare, and mainly include only isolated feathers.
An international team of scientists has analyzed a collection of 10 such fossil feathers found in Australia, which reveal an unexpected diversity of tufted hair-like 'proto-feathers' from meat-eating dinosaurs, together with downy body feathers, and wing feathers from primitive birds that would have been used for flight.
Uniquely, the fossil feathers from Australia were all entombed in fine muddy sediments that accumulated at the bottom of a shallow lake close to the South Pole during the Age of Dinosaurs.
"Dinosaur skeletons and even the fragile bones of early birds have been found at ancient high-latitudes before. Yet, to date, no directly attributable integumentary remains have been discovered to show that dinosaurs used feathers to survive in extreme polar habitats", said Dr Benjamin Kear from Uppsala University in Sweden, a leading author on the study.
"These Australian fossil feathers are therefore highly significant because they came from dinosaurs and small birds that were living in a seasonally very cold environment with months of polar darkness every year".
The fossil feathers were discovered in the Koonwarra Fish Beds Geological Reserve, which is a heritage listed site 145 km southeast of Melbourne in Victoria, Australia.
Carnivourous Dinosaur Protofeather from Koonwarra [Credit: Melbourne Museum]
"Fossil feathers have been known from Koonwarra since the early 1960s, and were recognized as evidence of ancient birds, but have otherwise received very little scientific attention. Our study is thus the first to comprehensively document these remains, which include new specimens that were examined using cutting-edge technologies", said Dr Thomas Rich of the Melbourne Museum in Australia, who has led numerous expeditions to the Koonwarra locality.
A suite of advanced microscopic and spectroscopic techniques was employed to determine the anatomy and preservation of the Koonwarra fossil dinosaur and bird feathers.
"The Koonwarra feathers are preserved in incredible detail", said fossil bird expert Professor Patricia Vickers-Rich of Monash University and the Swinburne University of Technology in Melbourne.
"There are even tiny filament-like structures that would have 'zipped' the feather vanes together, just as in the flight feathers of modern birds".
However, unlike the structurally complex feathers of birds today, which are characterized by interlocking branches called barbs and barbules, different kinds of small dinosaurs had coverings that comprised much more simpler hair-like 'proto-feathers'.
"Dinosaur 'proto-feathers' would have been used for insulation", said Dr Martin Kundrat, of Pavol Jozef Safarik University in Slovakia, a leading author on the study.
Early Bird Feather with Colour Patterning from Koonwarra [Credit: Melbourne Museum]
"The discovery of 'proto-feathers' at Koonwarra therefore suggests that fluffy feather coats might have helped small dinosaurs keep warm in ancient polar habitats".
Microscopic remains of possible melanosomes - cellular structures that contain colour pigments - were also detected on several of the fossil feathers found at Koonwarra.
These traces occurred across the uniformly dark feather surfaces, as well as in distinct bands that might represent original patterning from the polar dinosaurs and birds.
Melanic residues have been reported on fossil feathers from elsewhere around the world, and are widely acknowledged as indicators of dinosaur colouration.
The densely packed fossil melanosomes occurring on the Koonwarra feathers could suggest dark colours that perhaps assisted in camouflage, visual communication, and/or heat absorbance in cold polar climates.
Possible preservation of biomolecules was also assessed, but proved to be too degraded, and were apparently lost during weathering of the rock.
The Koonwarra fossil feathers provide the first record of dinosaur integument from the ancient polar regions, and hint what was once a global distribution of feathered dinosaurs and early birds.
Some of the fossil feathers found at Koonwarra are on display in the '600 Million Years' exhibition at the Melbourne Museum in Australia.
Despite bearing witness to its own increase in Earth's atmosphere by around 2.5 to 2.3 billion years ago, oxygen has had relatively little to say about its own early history until now. A recent EU-funded study provides a fresh perspective on one of Earth history's most significant stories—the rise of oxygen.
While the recent history of Earth's atmosphere can be accessed by directly measuring atmospheric gases trapped in ice cores, it may be surprising to know that a similarly faithful time capsule of atmospheric oxygen is not yet known for the majority of Earth history.
The rise of atmospheric oxygen is one of Earth history's greatest stories but this story is typically told through secondhand evidence, such as from proxies of sulfur stable isotope evidence from ancient rocks. Stable isotopes of sulfur are particularly helpful for understanding the time when oxygen first accumulated in Earth's atmosphere because they show a characteristic response to the increase in oxygen above 0.001% of today's atmospheric levels.
However, the record of how the sulfur isotope record in rocks responds to the first increases in atmospheric oxygen does not have a completely straightforward interpretation. Competition between global versus local, and original versus secondary, processes influence the preservation of chemical signals in ancient rocks. Accordingly, additional evidence is needed to support current interpretations of early atmospheric oxygen that are based on different proxies.
In a European-funded project involving an international team of researchers, newly published evidence from rocks younger than 2.31 billion years old from W. Australia now shows how stable isotope signals of sulfur that indicate exceedingly low oxygen may be recycled into rocks formed under increasing oxygen levels.
Oxygen itself is witness to this recycling. In fact, it is a characteristic isotope signal in oxygen that implies the formation of sulfur- and oxygen- bearing sulfates on the ancient continental surface at around 2.3 billion years ago. This sulfate was preserved in minerals, barites, in rocks that were formed in a marine environment close to shore, as evidenced by their coexistence with fossils from microbial mats, or stromatolites, unique wrinkly concave features (pictured in center of photo). Stable isotope results of oxygen and sulfur from the barites show how weathering of ancient rocks on the ancient Earth surface may prolong a signal that indicates a lack of atmospheric oxygen even after the rise of atmospheric oxygen.
The unique chemical, isotopic, signatures preserved in the reported barites hold further promise for unraveling the earliest history of oxygen gas production. Before substantial oxygen accumulated in the atmosphere, localized production of oxygen gas by microbial organisms (including the microbes that contributed to the aforementioned stromatolites) may have already been contributing to the oxidation, or the "rusting," of the Earth's surface. This early imprint of oxygen may, in the future, be similarly detected by the specific combination of sulfur and oxygen isotope signals that are detailed in the new study published in Nature Communications.
Swinburne and Museums Victoria have announced the discovery of several theropod bones, including a 20 centimeter long hand claw, from the Otway Coast of Victoria.
Fossilised 20 centimetre long hand claw of theropod discovered at Eric the West site on Victoria’s Otway Coast [Credit: Stephen Poropat/Museums Victoria]
The bones were found in the Eumeralla Formation, a geological deposit that is approximately 107 million years old.
Fossils of theropods—the group of dinosaurs that includes such famous predators as Tyrannosaurus and Velociraptor, as well as modern birds—are relatively rare in Australia. The new Victorian specimens were discovered at a site known as "Eric the Red West' on the Otway Coast between 2011 and 2017, by volunteers working on Dinosaur Dreaming team's annual digs.
These digs are held each February and are coordinated by husband and wife paleontologists, Swinburne's Professor Patricia Vickers-Rich and Dr. Thomas Rich from Museums Victoria.
Previously, the Eric the Red West site had produced the skeleton of Diluvicursor pickeringi, a unique species of ornithopod dinosaur that was described and named in 2018.
The new theropod fossils were found isolated rather than as part of a skeleton. This is because they were carried some distance from where the theropods died by ancient, deep, fast-flowing rivers. These rivers snaked through the then-narrow rift valley (now Bass Strait) that opened as Australia and Tasmania separated during the Early Cretaceous period, more than 110 million years ago.
Many of the theropod bones found at the Eric the Red West site are from a group of theropods called megaraptorids. Intriguingly, they look almost identical to those of the Australian megaraptorid theropod Australovenator wintonensis from western Queensland.
Australovenator lived around ten million years after—and thousands of kilometers further north than—the Victorian megaraptorid. This suggests that megaraptorid theropods roamed over a large part of Australia and for a long period of time.
The research on the new Victorian theropod remains was led by Swinburne's Dr. Stephen Poropat as part of a postdoctoral research fellowship in vertebrate palaeontology.
Artist's impression of Australovenator Wintonensis [Credit: Travis R. Tischler/ Australian Age of Dinosaurs Museum in Winton, Queensland]
According to Dr. Poropat, who has conducted research on Australian dinosaurs for several years, the presence of megaraptorid theropods in Victoria that are nearly indistinguishable from Australovenator—but older than it by around ten million years—is unusual.
"The similarities between the Victorian megaraptorid remains and Australovenator are striking," Dr. Poropat says.
"If we had found these theropod bones in Queensland, we would probably have called them Australovenator wintonensis. But they're from Victoria, which prompts the question: "Could one dinosaur species exist for more than ten million years, across eastern Australia?" Maybe."
Australovenator lived in Queensland around 95 million years ago, alongside several species of long-necked sauropod dinosaur (like Diamantinasaurus matildae and Savannasaurus elliottorum). However, the 107 million year-old rocks of western Victoria that produced the new theropod bones have not yielded a single scrap of sauropod bone.
"This is important, because it tells us that Australian megaraptorid theropods weren't entirely dependent on sauropods for food," says Dr. Poropat.
"We find megaraptorid teeth with sauropod carcasses in central Queensland all the time, but they seem to have been doing just fine in Victoria where sauropods seem to have been absent."
So were megaraptorid theropods relying on another food source in Victoria? Dr. Poropat thinks so. "Adult sauropods were many times heavier than adult megaraptorids, so attacking them would have been dangerous. What we do know is that another group of plant-eating dinosaurs—the ornithopods—were abundant in Victoria (based on bones) and in central Queensland (based on footprints).
"Although ornithopods might have been ideal meals for megaraptorids in both regions, Queensland's megaraptorids had another food choice—sauropod steaks! Whether they were fresh or on rotting carcasses, they would have been a pretty tempting item to have on the menu!"
The new theropod bones are held at Melbourne Museum. Another field trip to the Eric the Red West site is planned for November 2019. Dr. Poropat hopes that more megaraptorid bones might yet be found there.
New research into the chemistry of the oceans during ice ages is helping to solve a puzzle that has engaged scientists for more than two decades.
The Southern ocean, south-east of Tasmania [Credit: IMAS]
At issue is how much of the CO2 that entered the ocean during ice ages can be attributed to the 'biological pump', where atmospheric carbon is absorbed by phytoplankton and sequestered to the seafloor as organisms die and sink.
Solving the puzzle is important to improve the accuracy of climate models and inform understanding of how ocean processes may react to future climate change.
Led by IMAS and University of Liverpool scientists and published in Nature Communications, the study found ice age phytoplankton in the tropics absorbed high levels of CO2 due to fertilisation by iron-rich dust blowing into the ocean.
Lead author Dr Pearse Buchanan said that until now models had only been able to explain a portion of the CO2 that entered ice age oceans via the biological pump.
"During past ice ages, carbon levels were lower in the atmosphere and higher in the oceans than today, but scientific models aren't able to account for all of the additional CO2 that entered the ocean," Dr Buchanan said.
"The leading hypothesis has been that iron-rich dust blown from glacial landscapes stimulated phytoplankton growth in high latitudes, but this only explained around one-third of the extra CO2 absorbed through the biological pump: the other two-thirds was effectively 'missing'.
"We used an ocean model to look at the response to iron rich dust of phytoplankton in tropical waters, particularly a group of phytoplankton called "nitrogen fixers".
"These are able to biochemically 'fix' nitrogen from the atmosphere, much like nitrogen fixing bacteria that help legume crops thrive in nutrient poor soil.
"Marine nitrogen fixers are known to be important in the marine nitrogen cycle, and now we've shown they're also critically important in the marine carbon cycle.
"When we added iron to our ocean model, nitrogen fixers thrived, and their growth and subsequent sinking to the deep ocean can account for much of the missing CO2," Dr Buchanan said.
IMAS Associate Professor Zanna Chase said this solution was first proposed in 1997 but had gained little traction over the last two decades.
"The beauty of this approach is that it can explain almost all of the additional CO2 that phytoplankton transported into the oceans during the last Ice Age," Associate Professor Chase said.
"The increased activity of the biological pump in the tropics complemented that happening in colder waters, drawing higher levels of CO2 into the oceans and locking it away in the deep ocean.
"This pathway for carbon to the deep ocean is reduced today because less fertilising iron is being circulated by the wind and phytoplankton growth, including that of nitrogen fixers, is correspondingly limited, although there are signs that it has strengthened within the Pacific since the industrial revolution.
"Taking account of these links between the cycles of iron, nitrogen and carbon in our ocean and climate change models will make them better able to explain ocean processes and predict future changes.
"But how iron fertilisation of phytoplankton will evolve is currently uncertain, undermining our ability to predict the ocean's role in drawing CO2 out of the atmosphere in the coming centuries," Associate Professor Chase said.
Slime has been present on Earth for a very long time—almost 2 billion years, according to a recent reassessment of fossil evidence.
Credit: University of Oregon
In a study published this month in the journal Palaeogeography, Palaeoclimatology, Palaeoecology, UO geologist Greg Retallack and Xuegang Mao of China's Fujian Normal University confirm that a fossil from Western Australia is the planet's oldest known land-dwelling slime mold.
The fossil in question, Myxomitodes stirlingensi, is a hairpin-shaped trace of biological activity found in the rocks of the Stirling Range, a mountain region 200 miles southeast of Perth. Long the subject of scholarly controversy, the fossil has sparked debate both about the specific life form it represents as well as the paleoenvironment it inhabited.
"They have been interpreted as trails of metazoan animals and often as marine organisms," said Retallack, who is director of the Condon Fossil Collection at the Museum of Natural and Cultural History. "Though they resemble animal trails they probably were not. Slime molds make similar trails but lack any animal organization: no mouth, no gut, no anus, no nerves, no veins. And we are seeing these fossils at the surface of ancient terrestrial soils, making them additional evidence of life on land during the Paleoproterozoic Period."
Retallack said that while slime molds are not themselves multicellular, they might hold important clues about how multicellular organisms evolved.
"Myxomitodes were amoebae that live dispersed in soil, but these traces of their movement demonstrate that they could coalesce into a slug that wandered over the soil as a unit, possibly to sense better feeding opportunities or a place to sporulate, and then disaggregate once again into single cells," he said. "This may demonstrate an early stage in the evolution of multicellular creatures, bridging the gap between microbes and more complex life forms."
