Rising CO₂ levels helped end the last ice age, but the cause of this CO₂ rise has puzzled scientists for decades. Using geochemical fingerprinting of fossil corals, an international team of scientists has found new evidence that this CO₂ rise was linked to extremely rapid changes in ocean circulation around Antarctica.

The team collected fossil remains of deep-sea corals that lived thousands of metres beneath the waves. By studying the radioactive decay of the tiny amounts of uranium found in these skeletons, they identified corals that grew at the end of the ice age around 15,000 years ago.

Further geochemical fingerprinting of these specimens — including measurements of radiocarbon — allowed the team to reconstruct changes in ocean circulation and compare them to changes in global climate at an unprecedented time resolution.

Professor Laura Robinson, Professor of Geochemistry at Bristol’s School of Earth Sciences who led the research team, said: “The data show that deep ocean circulation can change surprisingly rapidly, and that this can rapidly release CO₂ to the atmosphere.”

Dr James Rae at St Andrew’s School of Earth and Environmental Sciences, added: “The corals act as a time machine, allowing us to see changes in ocean circulation that happened thousands of years ago.

“They show that the ocean round Antarctica can suddenly switch its circulation to deliver burps of CO₂ to the atmosphere.”

Scientists have suspected that the Southern Ocean played an important role in ending the last ice age and the team’s findings add weight to this idea.

Dr Tao Li of Nanjing University, lead author of the new study, said: “There is no doubt that Southern Ocean processes must have played a critical role in these rapid climate shifts and the fossil corals provide the only possible way to examine Southern Ocean processes on these timescales.”

In another study published in Nature Geoscience this week the same team ruled out recent speculation that the global increase in CO₂ at the end of the ice age may have been related to release of geological carbon from deep sea sediments.

Andrea Burke at St Andrew’s School of Earth and Environmental Sciences, added: “There have been some suggestions that reservoirs of carbon deep in marine mud might bubble up and add CO₂ to the ocean and the atmosphere, but we found no evidence of this in our coral samples.”

Dr Tianyu Chen of Nanjing University said: “Our robust reconstructions of radiocarbon at intermediate depths yields powerful constraints on mixing between the deep and upper ocean, which is important for modelling changes in circulation and carbon cycle during the last ice age termination.

Dr James Rae added: “Although the rise in CO₂ at the end of the ice age was dramatic in geological terms, the recent rise in CO₂ due to human activity is much bigger and faster. What the climate system will do in response is pretty scary.”

1. Tao Li, Laura F. Robinson, Tianyu Chen, Xingchen T. Wang, Andrea Burke, James W. B. Rae, Albertine Pegrum-Haram, Timothy D. J. Knowles, Gaojun Li, Jun Chen, Hong Chin Ng, Maria Prokopenko, George H. Rowland, Ana Samperiz, Joseph A. Stewart, John Southon, Peter T. Spooner. Rapid shifts in circulation and biogeochemistry of the Southern Ocean during deglacial carbon cycle events. Science Advances, 2020; 6 (42): eabb3807 DOI: 10.1126/sciadv.abb3807
2. Source: University of Bristol. “Deep sea coral time machines reveal ancient CO2 burps.” ScienceDaily. ScienceDaily, 16 October 2020. <www.sciencedaily.com/releases/2020/10/201016164230.htm>.

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Coloradoan Gary Thompson discovered mosasaur bones near the Delta County town of Cedaredge in 1975, which the teen reported to his high school science teacher. The specimens made their way to Utah’s Brigham Young University, where, in 1999, the creature that left the fossils was named Prognathodon stadtmani.

“I first learned of this discovery while doing background research for my Ph.D.,” says newly arrived Utah State University Eastern paleontologist Joshua Lively, who recently took the reins as curator of the Price campus’ Prehistoric Museum. “Ultimately, parts of this fossil, which were prepared since the original description in 1999, were important enough to become a chapter in my 2019 doctoral dissertation.”

Upon detailed research of the mosasaur’s skeleton and a phylogenetic analysis, Lively determined the BYU specimen is not closely related to other species of the genus Prognathodon and needed to be renamed. He reclassified the mosasaur as Gnathomortis stadtmani and reports his findings in the most recent issue of the Journal of Vertebrate Paleontology.

His research was funded by the Geological Society of America, the Evolving Earth Foundation, the Texas Academy of Science and the Jackson School of Geosciences at The University of Texas at Austin.

“The new name is derived from Greek and Latin words for ‘jaws of death,'” Lively says. “It was inspired by the incredibly large jaws of this specimen, which measure four feet (1.2 meters) in length.”

An interesting feature of Gnathomortis’ mandibles, he says, is a large depression on their outer surface, similar to that seen in modern lizards, such as the Collared Lizard. The feature is indicative of large jaw muscles that equipped the marine reptile with a formidable biteforce.

“What sets this animal apart from other mosasaurs are features of the quadrate — a bone in the jaw joint that also forms a portion of the ear canal,” says Lively, who returned to the fossil’s Colorado discovery site and determined the age interval of rock, in which the specimen was preserved.

“In Gnathomortis, this bone exhibits a suite of characteristics that are transitional from earlier mosasaurs, like Clidastes, and later mosasaurs, like Prognathodon. We now know Gnathomortis swam in the seas of Colorado between 79 and 81 million years ago, or at least 3.5 million years before any species of Prognathodon.”

He says fossil enthusiasts can view Gnathomortis’ big bite at the BYU Museum of Paleontology in Provo, Utah, and see a cast of the skull at the Pioneer Town Museum in Cedaredge, Colorado. Reconstructions of the full skeleton are on display at the John Wesley Powell River History Museum in Green River, Utah, and in BYU’s Eyring Science Center.

“I’m excited to share this story, which represents years of effort by many citizen scientists and scholars, as I kick off my new position at USU Eastern’s Prehistoric Museum,” Lively says. “It’s a reminder of the power of curiosity and exploration by people of all ages and backgrounds.”

1. Joshua R. Lively. Redescription and phylogenetic assessment of ‘Prognathodon’ stadtmani: implications for Globidensini monophyly and character homology in Mosasaurinae. Journal of Vertebrate Paleontology, 2020; e1784183 DOI: 10.1080/02724634.2020.1784183
2. Utah State University. “Jaws of death: Paleontologist renames giant, prehistoric marine lizard.” ScienceDaily. ScienceDaily, 23 September 2020. <www.sciencedaily.com/releases/2020/09/200923090424

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Researchers at Columbia University’s Lamont-Doherty Earth Observatory examined ocean conditions 55.6 million years ago, a time known as the Paleocene-Eocene Thermal Maximum (PETM). Before this, the planet was already considerably warmer than it is today, and the soaring CO₂ levels of the PETM drove temperatures up another 5 to 8 degrees C (9 to 14 degrees F). The oceans absorbed large amounts of carbon, spurring chemical reactions that caused waters to become highly acidic, and killing or impairing many marine species.

Scientists have known about the PETM carbon surge for years, but until now, have been shaky on what caused it. Aside from volcanism, hypotheses have included the sudden dissolution of frozen methane (which contains carbon) from ocean-floor muds, or even a collision with a comet. Researchers have also been uncertain about how much carbon dioxide was present in the air, and thus how much the oceans took in. The new study solidifies both the volcano theory, and the amount of carbon that was released into the air.

The research is directly relevant to today, said lead author Laura Haynes, who did the research as a graduate student at Lamont-Doherty. “We want to understand how the earth system is going to respond to rapid CO₂ emissions now,” she said. “The PETM is not the perfect analog, but it’s the closest thing we have. Today, things are moving much faster.” Haynes is now an assistant professor at Vassar College.

Up to now, marine studies of the PETM have relied on scant chemical data from the oceans, and assumptions based on a certain degree of guesswork that researchers fed into computer models.

The authors of the new study got at the questions more directly. They did this by culturing tiny shelled marine organisms called foraminifera in seawater that they formulated to resemble the highly acidic conditions of the PETM. They recorded how the organisms took up the element boron into their shells during growth. They then compared these data with analyses of boron from fossilized foraminifera in Pacific and Atlantic ocean-floor cores that span the PETM. This allowed them to identify carbon-isotope signatures associated with specific carbon sources. This indicated that volcanoes were the main source — probably from massive eruptions centered around what is now Iceland, as the North Atlantic ocean opened up, and northern North America and Greenland separated from northern Europe.

The researchers say the carbon pulses, which others estimate lasted for at least 4,000 to 5,000 years, added as much as 14.9 quadrillion metric tons of carbon to the oceans — a two-thirds increase over their previous content. The carbon would have come from CO₂ emitted directly by the eruptions, the combustion of surrounding sedimentary rocks, and some methane welling up from the depths. As the oceans absorbed carbon from the air, waters became highly acidic, and remained that way for tens of thousands of years. There is evidence that this killed off much deep-sea life, and probably other marine creatures as well.

Today, human emissions are causing carbon dioxide in the atmosphere to skyrocket, and the oceans are again absorbing much of it. The difference is that we are introducing it much faster than the volcanoes did — within decades instead of millennia. Atmospheric levels have shot up from about 280 parts per million in the 1700s to about 415 today, and they are on a path to keep rising rapidly. Atmospheric levels would already be much higher if the oceans were not absorbing so much. As they do, rapid acidification is starting to stress marine life.

“If you add carbon slowly, living things can adapt. If you do it very fast, that’s a really big problem,” said the study’s coauthor Bärbel Hönisch, a geochemist at Lamont-Doherty. She pointed out that even at the much slower pace of the PETM, marine life saw major die-offs. “The past saw some really dire consequences, and that does not bode well for the future,” she said. “We’re outpacing the past, and the consequences are probably going to be very serious.”

1. Laura L. Haynes, Bärbel Hönisch. The seawater carbon inventory at the Paleocene–Eocene Thermal Maximum. Proceedings of the National Academy of Sciences, 2020; 202003197 DOI: 10.1073/pnas.2003197117

The DNA extraction method, outlined in the journal Quarternary Research, allows scientists to reconstruct the most advanced picture ever of environments that existed thousands of years ago.

The researchers analyzed permafrost samples from four sites in the Yukon, each representing different points in the Pleistocene-Halocene transition, which occurred approximately 11,000 years ago.

This transition featured the extinction of a large number of animal species such as mammoths, mastodons and ground sloths, and the new process has yielded some surprising new information about the way events unfolded, say the researchers. They suggest, for example, that the woolly mammoth survived far longer than originally believed.

In the Yukon samples, they found the genetic remnants of a vast array of animals, including mammoths, horses, bison, reindeer and thousands of varieties of plants, all from as little as 0.2 grams of sediment.

The scientists determined that woolly mammoths and horses were likely still present in the Yukon’s Klondike region as recently as 9,700 years ago, thousands of years later than previous research using fossilized remains had suggested.

“That a few grams of soil contains the DNA of giant extinct animals and plants from another time and place, enables a new kind of detective work to uncover our frozen past,” says evolutionary geneticist Hendrik Poinar, a lead author on the paper and director of the McMaster Ancient DNA Centre. “This research allows us to maximize DNA retention and fine-tune our understanding of change through time, which includes climate events and human migration patterns, without preserved remains.”

The technique resolves a longstanding problem for scientists, who must separate DNA from other substances mixed in with sediment. The process has typically required harsh treatments that actually destroyed much of the usable DNA they were looking for. But by using the new combination of extraction strategies, the McMaster researchers have demonstrated it is possible to preserve much more DNA than ever.

“All of the DNA from those animals and plants is bound up in a tiny speck of dirt,” explains Tyler Murchie, a PhD candidate in the Department of Anthropology and a lead author of the study.

“Organisms are constantly shedding cells throughout their lives. Humans, for example, shed some half a billion skin cells every day. Much of this genetic material is quickly degraded, but some small fraction is safeguarded for millenia through sedimentary mineral-binding and is out there waiting for us to recover and study it. Now, we can conduct some remarkable research by recovering an immense diversity of environmental DNA from very small amounts of sediment, and in the total absence of any surviving biological tissues.”

There is a grim fascination in determining the size of the largest sharks, but this can be difficult for fossil forms where teeth are often all that remain.

Today, the most fearsome living shark is the Great White, at over six metres (20 feet) long, which bites with a force of two tonnes.

Its fossil relative, the big tooth shark Megalodon, star of Hollywood movies, lived from 23 to around three million years ago, was over twice the length of a Great White and had a bite force of more than ten tonnes.

The fossils of the Megalodon are mostly huge triangular cutting teeth bigger than a human hand.

Jack Cooper, who has just completed the MSc in Palaeobiology at the University of Bristol’s School of Earth Sciences, and colleagues from Bristol and Swansea used a number of mathematical methods to pin down the size and proportions of this monster, by making close comparisons to a diversity of living relatives with ecological and physiological similarities to Megalodon.

The project was supervised by shark expert Dr Catalina Pimiento from Swansea University and Professor Mike Benton, a palaeontologist at Bristol. Dr Humberto Ferrón of Bristol also collaborated.

Their findings are published today in the journal Scientific Reports.

Jack Cooper said: “I have always been mad about sharks. As an undergraduate, I have worked and dived with Great whites in South Africa — protected by a steel cage of course. It’s that sense of danger, but also that sharks are such beautiful and well-adapted animals, that makes them so attractive to study.

“Megalodon was actually the very animal that inspired me to pursue palaeontology in the first place at just six years old, so I was over the moon to get a chance to study it.

“This was my dream project. But to study the whole animal is difficult considering that all we really have are lots of isolated teeth.”

Previously the fossil shark, known formally as Otodus megalodon, was only compared with the Great White. Jack and his colleagues, for the first time, expanded this analysis to include five modern sharks.

Dr Pimiento said: “Megalodon is not a direct ancestor of the Great White but is equally related to other macropredatory sharks such as the Makos, Salmon shark and Porbeagle shark, as well as the Great white. We pooled detailed measurements of all five to make predictions about Megalodon.”

Professor Benton added: “Before we could do anything, we had to test whether these five modern sharks changed proportions as they grew up. If, for example, they had been like humans, where babies have big heads and short legs, we would have had some difficulties in projecting the adult proportions for such a huge extinct shark.

“But we were surprised, and relieved, to discover that in fact that the babies of all these modern predatory sharks start out as little adults, and they don’t change in proportion as they get larger.”

Jack Cooper said: “This means we could simply take the growth curves of the five modern forms and project the overall shape as they get larger and larger — right up to a body length of 16 metres.”

The results suggest that a 16-metre-long Otodus megalodon likely had a head round 4.65 metres long, a dorsal fin approximately 1.62 metres tall and a tail around 3.85 metres high.

This means an adult human could stand on the back of this shark and would be about the same height as the dorsal fin.

The reconstruction of the size of Megalodon body parts represents a fundamental step towards a better understanding of the physiology of this giant, and the intrinsic factors that may have made it prone to extinction.

• Journal Reference:

1. Jack A. Cooper, Catalina Pimiento, Humberto G. Ferrón, Michael J. Benton. Body dimensions of the extinct giant shark Otodus megalodon: a 2D reconstruction. Scientific Reports, 2020; 10 (1) DOI: 10.1038/s41598-020-71387-y

Until now, this question could only be addressed by studying living animals and their relatives, but now the research team has found evidence that a key step in this major evolutionary transition occurred long before complex animals appear in the fossil record, in the fossilised embryos that resemble multicellular stages in the life cycle of single-celled relatives of animals.

The team discovered the fossils named Caveasphaera in 609 million-year old rocks in the Guizhou Province of South China. Individual Caveasphaera fossils are only about half a millimeter in diameter, but X-ray microscopy revealed that they were preserved all the way down to their component cells.

Kelly Vargas, from the University of Bristol’s School of Earth Sciences, said: “X-Ray tomographic microscopy works like a medical CT scanner, but allows us to see features that are less than a thousandth of a millimeter in size. We were able to sort the fossils into growth stages, reconstructing the embryology of Caveasphaera.”

Co-author Zongjun Yin, from Nanjing Institute of Geology and Palaeontology in China, added: “Our results show that Caveasphaera sorted its cells during embryo development, in just the same way as living animals, including humans, but we have no evidence that these embryos developed into more complex organisms.”

Co-author Dr John Cunningham, also from University of Bristol, said: “Caveasphaera had a life cycle like the close living relatives of animals, which alternate between single-celled and multicellular stages. However, Caveasphaera goes one step further, reorganising those cells during embryology.”

Co-author Stefan Bengtson, from the Swedish Museum of Natural History, said “Caveasphaera is the earliest evidence of this most important step in the evolution of animals, which allowed them to develop distinct tissue layers and organs.”

Co-author Maoyan Zhu, also from Nanjing Institute of Geology and Palaeontology, said he is not totally convinced that Caveasphaera is an animal. He added: “Caveasphaera looks a lot like the embryos of some starfish and corals — we don’t find the adult stages simply because they are harder to fossilise

Co-author Dr Federica Marone from the Paul Scherrer Institute in Switzerland said “this study shows the amazing detail that can be preserved in the fossil record but also the power of X-ray microscopes in uncovering secrets preserved in stone without destroying the fossils.”

Co-author Professor Philip Donoghue, also from the University of Bristol’s School of Earth Sciences, said “Caveasphaera shows features that look both like microbial relatives of animals and early embryo stages of primitive animals. We’re still searching for more fossils that may help us to decide.

“Either way, fossils of Caveasphaera tell us that animal-like embryonic development evolved long before the oldest definitive animals appear in the fossil record.”

This research was funded through the Biosphere Evolution, Transitions and Resilience (BETR) programme, which is co-funded by the Natural Environment Research Council (NERC) and Natural Science Foundation of China (NSFC).

Journal: Zongjun Yin, Kelly Vargas, John Cunningham, Stefan Bengtson, Maoyan Zhu, Federica Marone, Philip Donoghue. The Early Ediacaran Caveasphaera Foreshadows the Evolutionary Origin of Animal-like Embryology. Current Biology, 2019; DOI: 10.1016/j.cub.2019.10.057

Source: sciencedaily.com

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