Categories
Earth & Climate Events Feature Fossils & Ruins Learning & Education Plants & Animals Researcher news Student researchers

Ancient “Sea Monsters” Reveal How the Ever-Changing Planet Shapes Life, Past and Present

Never-Before-Seen Fossils From Angola Bring a Strange Yet Familiar Ocean Into View

The Smithsonian’s National Museum of Natural History will open a new exhibition Nov. 9, 2018 revealing how millions of years ago, large-scale natural forces created the conditions for real-life sea monsters to thrive in the South Atlantic Ocean basin shortly after it formed. “Sea Monsters Unearthed: Life in Angola’s Ancient Seas” will offer visitors the opportunity to dive into Cretaceous Angola’s cool coastal waters, examine the fossils of striking marine reptiles that once lived there and learn about the forces that continue to mold life in the ocean and on land.

Over 134 million years ago, the South Atlantic Ocean basin did not yet exist. Africa and South America were one contiguous landmass on the verge of separating. As the two continents drifted apart, an entirely new marine environment — the South Atlantic — emerged in the vast space created between them. This newly formed ocean basin would soon be colonized by a dizzying array of ferocious predators and an abundance of other lifeforms seizing the opportunity presented by a new ocean habitat.

“Because of our planet’s ever-shifting geology, Angola’s coastal cliffs contain the fossil remains of marine creatures from the prehistoric South Atlantic,” said Kirk Johnson, the Sant Director of the museum. “We are honored by the generosity of the Angolan people for sharing a window into this part of the Earth’s unfolding story with our visitors.”

For the first time, Angolan fossils of colossal Cretaceous marine reptiles will be on public display. Through Projecto PaleoAngola — a collaboration between Angolan, American, Portuguese and Dutch researchers focused on Angola’s rich fossil history — paleontologists excavated and studied these fossils, which were then prepared for the exhibition by a team of scientists and students at Southern Methodist University (SMU) in Dallas. The exhibition was made possible by the Sant Ocean Hall Endowment Fund.

“Fossils tell us about the life that once lived on Earth, and how the environments that came before us evolve over time,” said Louis Jacobs, professor emeritus of paleontology at SMU and collaborating curator for the exhibition. “Our planet has been running natural experiments on what shapes environments, and thereby life, for millions of years. If it weren’t for the fossil record, we wouldn’t understand what drives the story of life on our planet.”

The exhibition will immerse visitors in this Cretaceous environment with lively animations and vivid paleoart murals of life beneath the waves — courtesy of natural history artist Karen Carr — that bring to life 11 authentic fossils from Angola’s ancient seas, full-size fossil reconstructions of a mosasaur and an ancient sea turtle, as well as 3-D scanned replicas of mosasaur skulls. Photomurals and video vignettes will transport visitors to field sites along Angola’s modern rugged coast, where Projecto PaleoAngola scientists unearth the fossil remains from this lost world.

A Strange but Familiar Ocean
“Sea Monsters Unearthed” paints the picture of a flourishing ocean environment that in some ways will look strange to modern eyes, yet still bears striking similarities to today’s marine ecosystems.

Peculiar plesiosaurs — massive reptiles with long necks, stout bodies and four large flippers — swam alongside 27-foot-long toothy marine lizards called mosasaurs and more familiar creatures like sea turtles. From surprising mosasaur stomach contents to the one of the oldest known sea turtles found in Africa, fossils and reconstructions of these species will offer visitors a fuller picture of their remarkable life histories and the ecosystems they were a part of.

The exhibition will also explore deeper similarities across the ecology and anatomy of ocean animals then and now. After the marine reptiles that dominated these waters went extinct 66 million years ago, modern marine mammals would not only later replace them as top predators in the world’s ocean, but also converge on many of the same body shapes and survival strategies.

The Forces That Shape Life, Then and Now
This unique period in Earth’s history reveals how key geologic and environmental forces contributed to the early establishment and evolution of life in the South Atlantic. As Africa and South America drifted apart and a new ocean basin formed, trade winds blowing along the new Angolan coastline created the conditions for upwelling, an ocean process that drives the circulation of nutrients from the deep ocean to its surface. These nutrients in turn jump-started the food web that attracted the ferocious marine reptile predators featured throughout the exhibition.

Just as tectonic forces helped create this Cretaceous marine environment, they also shaped the arid coastal cliffs where the fossils are found today. Starting 45,000 years ago, a geologic process called uplift caused Earth’s crust to bulge along Angola’s coast, lifting part of the seafloor out of the water — and along with it, the layers upon layers of fossil-filled rocks where Projecto PaleoAngola scientists work.

Though humans do not operate on a tectonic scale, their actions also have major impacts on ocean life. Humans are now the ocean’s top predators, with one-fifth of the world’s population relying on food from upwelling-based ecosystems. Scientists caution that with such great pressure on modern upwelling-based fisheries, overfishing could change the future of life in the ocean by threatening fish populations, marine ecosystems and even human health. — National Museum of Natural History

About the National Museum of Natural History
The National Museum of Natural History is connecting people everywhere with Earth’s unfolding story. The museum is one of the most visited natural history museums in the world with approximately 7 million annual visitors from the U.S. and around the world. Opened in 1910, the museum is dedicated to maintaining and preserving the world’s most extensive collection of natural history specimens and human artifacts. It is open daily from 10 a.m. to 5:30 p.m. (closed Dec. 25). Admission is free. For more information, visit the museum on its website and on Facebook and Twitter.

Categories
Feature Health & Medicine Plants & Animals Researcher news

Study: Cells of three aggressive cancers annihilated by drug-like compounds that reverse chemo failure

Wet-lab experiments confirm the accuracy of an earlier computational discovery that three drug-like compounds successfully penetrate micro-tumors of advanced cancers to aid chemo in destroying the cancer.

Researchers at Southern Methodist University have discovered three drug-like compounds that successfully reverse chemotherapy failure in three of the most commonly aggressive cancers — ovarian, prostate and breast.

The molecules were first discovered computationally via high-performance supercomputing. Now their effectiveness against specific cancers has been confirmed via wet-lab experiments, said biochemistry professors Pia Vogel and John G. Wise, who led the study.

Wise and Vogel report the advancement in the Nature journal Scientific Reports.

The computational discovery was confirmed in the Wise-Vogel labs at SMU after aggressive micro-tumors cultured in the labs were treated with a solution carrying the molecules in combination with a classic chemotherapy drug. The chemotherapy drug by itself was not effective in treating the drug-resistant cancer.

“Nature designs all cells with survival mechanisms, and cancer cells are no exception,” said Vogel, a professor in the SMU Department of Biological Sciences and director of SMU’s Center for Drug Discovery, Design and Delivery. “So it was incredibly gratifying that we were able to identify molecules that can inhibit that mechanism in the cancer cells, thereby bolstering the effectiveness of chemotherapeutic drugs. We saw the drugs penetrate these resistant cancer cells and allow chemotherapy to destroy them. While this is far from being a developed drug that will be available on the market anytime soon, this success in the lab gives us hope for developing new drugs to fight cancer.”

The current battle to defeat cancer is thwarted by chemotherapy failure in advanced cancers. Cancer cells initially treated with chemotherapy drugs ultimately evolve to resist the drugs. That renders chemotherapy ineffective, allowing cancers to grow and spread.

Key to cancer cell resistance are often certain proteins typically found in all cells — cancerous or otherwise — that are outfitted with beneficial mechanisms that pump away toxins to ensure a cell’s continued survival. Nature has set it up that these pumps are prevalent throughout the body, with some areas naturally having more of the pumps than others.

“The cancer cell itself can use all these built-in defenses to protect it from the kinds of things we’re using to try to kill it with,” Wise said.

The most common of these beneficial defense mechanisms is a pump protein, P-glycoprotein or P-gp, as it’s called. Another is one seen in breast and many other cancers, called breast cancer resistance protein, BCRP. In the case of cancer cells on the first round of treatment, these pumps are typically not produced in high levels in the cells, which allows chemotherapy to enter most of the cells in the tumor. This often gives what looks like a good result.

Unfortunately, in the cancer cells that don’t die, the chemotherapeutic often changes the cell, which then adapts to protect itself by aggressively multiplying the production of its defensive pumps.

Upon subsequent rounds of chemo, the P-gp and BCRP pumping mechanisms have proliferated. They effectively resist the chemotherapy, which now is much less successful, or not successful at all.

“if enough of the pumps are present, the cancer isn’t treatable anymore,” said Wise, associate professor in the SMU Department of Biological Sciences. Researchers in the field have searched unsuccessfully for compounds to inhibit the pumps that could be used in the clinic as well.

The molecules that Wise and Vogel discovered stopped the pumps.

“They effectively bring the cancer cells back to a sensitivity as if they’d never seen chemotherapy before,” said Vogel. “And our data indicated the molecules aren’t cancer specific. They can be used to treat all kinds of cancers because they inhibit not just the P-gp pump, but also the breast cancer protein pump.”

To test the compounds, the researchers used amounts of chemotherapeutic that would not kill these multi-drug resistant cancers if the pumps were not blocked.

“We wanted to make sure when using these really aggressive cancers that if we do knock out the pump, that the chemotherapy goes in there and causes the cell to die, so it doesn’t just stop it temporarily,” Wise said. “We spent a fair amount of time proving that point. It turns out that when a cell dies it goes through very predictable morphological changes. The DNA gets chopped up into small pieces, and we can see that, and so the nucleus becomes fragmented, and we can see that. Under the microscope, with proper staining, you can actually see that these highly drug-resistant prostate cancer cells, for example, are dead.”

The Scientific Reports article, “Targeted inhibitors of P-glycoprotein increase chemotherapeutic-induced mortality of multidrug resistant tumor cells,” is available open access at this link.

Other co-authors are SMU Ph.D. doctoral candidate Amila K. Nanayakkara, and Courtney A. Follit and Gang Chen, all in the SMU Department of Biological Sciences; and Noelle S. Williams, Department of Biochemistry, UT Southwestern Medical Center, Dallas.

Getting at the heart of the problem
Unique to the experiment is that the molecules were also tested on three-dimensional micro-tumors. That is a departure from the usual cell-culture experiments, which are a two-dimensional film.

In two-dimensional experiments, every cell is exposed to the chemotherapeutic because the film is just one layer of cells thick. That method ignores one of the key challenges to reversing tumors — how to get drugs into the middle of a tumor, not just on its surface.

“We show that with the help of our inhibitor compounds, we actually make the tumor penetrable to chemotherapeutic,” Vogel said. “We can kill the cells in the middle of the tumor.”

A pathway to personalized medical treatments
Chemotherapy’s harmful side effects on non-cancerous organs is well-known. The discovery of molecules that target a specific pump may mitigate that problem.

A patient’s tumor can be sampled to see which pump is causing the drug resistance. Then the molecule that knocks out that specific pump can be added to the chemotherapy.

“That means you don’t open the door wide to toxins in the central nervous system,” Wise said. “That has some real implications for the future and for personalized medicine. In most of the previous clinical trials, inhibitors have opened the brain up to toxins. From what we can tell so far, our inhibitors do not increase the toxicity of chemotherapeutics in normal cells.”

An audacious discovery
P-gp is present in one form or another in everything that lives.

“It’s in your dog, it’s in your cat, it’s in yeast cells, it’s in bacteria, it’s everywhere,” Wise said. “Why is it everywhere? Because it’s a really wonderful solution to the problem of getting toxins out of a cell. P-gp is a tremendously sophisticated evolutionary solution to that problem. And as with most things in biology that work well, everybody gets it, because if you don’t have it, you didn’t survive.”

Biologists say that P-gp can pump out 95 of 100 chemotherapeutics, indicating it can grab almost any drug and throw it out of a cell.

“So there’s a certain audacity to say that we can use a computer and target one part of this protein — the motor — and totally avoid the part of the protein that has evolved to pump almost anything that looks like a drug out of the cell,” Wise said. “That’s an audacious claim and the findings surprised us.”

In their computational and wet-lab experiments, Wise and Vogel searched for molecules that inhibit ATP hydrolysis — the chemical energy reaction that powers the P-gp pump.

“We targeted the motor of the pump instead of the pump part of the pump because almost all the clinical trial failures in other studies were actually compounds that targeted the pump part of the pump — and they would just slow down the pumping of the chemotherapeutic,” Vogel said. “The time was ripe to do these structural models. We hypothesized that we could completely avoid the pumping mechanism and just target the motor.”

Computational method highly predictive
The wet-lab experiments confirmed the accuracy of the computational findings, Vogel said.

“The predictiveness of the computational methods was really high,” she said. “It completely exceeded my expectations. We had selected certain molecules that were predicted in those computational experiments to interact with the pump in certain ways and not in others, and we could show in our wet-lab experiments that the predictions were spot on.”

Fascinated by the novel approach to the research, the National Institute of General Medical Sciences funded much of the research.

Wise and Vogel tapped the high-performance computing power of SMU’s Maneframe, one of the most powerful academic supercomputers in the nation. Wise sorted through 15 million commercially available drug-like compounds made publically available in digital form from the pharmacology database Zinc at the University of California, San Francisco.

Then, again using ManeFrame, Wise ran the compounds through a computer-generated model of P-gp. The virtual model, designed and built by Wise, is the first computational microscope of its kind to simulate the actual behavior of P-gp in the human body, including interactions with drug-like compounds while taking on different shapes. He reported the dynamic functioning of the model in 2015 in the journal Biochemistry in “Multiple drug transport pathways through human P-glycoprotein.”

Process of elimination finds needle in the haystack
Out of 15 million drug-like compounds that were virtually screened, the researchers found 180,000 that in the computer were predicted to interact strongly with the ATP harvesting power plant part of the pump motor. From those, Wise and Vogel eliminated the ones that interact well with the pump part. Roughly 0.15 percent survived — several hundred.

“So that tells you how promiscuous that binding site is for compounds,” Wise said.

From there, they bought and tested in the lab a number of the remaining molecules.

“It was a process of elimination,” Vogel said. “Of the first 38 we tested, we found four. And because of the computational approach we took, it made failure relatively cheap. This is proof of principle that at least in those cases the compounds behave exactly in the lab as predicted in the computer. Which thrills the heck out of me — I never, ever would have thought that.”

The Vogel and Wise research labs are part of the Center for Drug Discovery, Design and Delivery in SMU’s Dedman College. The center’s mission is a novel multi-disciplinary focus for scientific research targeting medically important problems in human health. — Margaret Allen, SMU

Categories
Culture, Society & Family Earth & Climate Economics & Statistics Feature Plants & Animals Researcher news

Commerce Department selects scientific team to conduct independent abundance estimate of red snapper in Gulf of Mexico

The initiative addresses one of the most pressing issues currently facing U.S. Gulf of Mexico fisheries management, as the iconic red snapper supports one of the most economically valuable finfish fisheries in the Gulf.

An expert team of university and government scientists will determine the abundance of red snapper in the U.S. waters of the Gulf of Mexico, as availability of the fish is vital to the region’s economy.

“Red snapper have great economic value to all the gulf states,” said SMU statistician Lynne Stokes, a member of the team. “Maintaining the health of the species is vitally important, so it’s necessary to ensure species are fished at the right level.”

As an expert in surveys, polls and sampling, Stokes’ role in the project is to help design ways to sample the vast expanse of the gulf efficiently so that good estimates of abundance can be produced.

“The gulf is very diverse, and different sampling methods are needed for different habitats, which makes the sample design problem interesting,” said Stokes, a professor in the SMU Department of Statistical Science. “The cheapest way to collect data about the health of a marine fish species is by asking a sample of anglers about their catch. However, if fish are present in places where anglers are not, other methods are needed. There is some uncertainty about all the places red snapper exist in the gulf, so it is not known if catch-based methods provide accurate estimates of abundance.”

The project will obtain angler-independent data about red snapper abundance by sampling their potential habitat, Stokes said. The team will collect data on red snapper numbers by direct observation of a sample of transects on the sea bottom and structures on the sea floor, using remotely controlled video cameras. Stokes will help determine how extensive the observation must be.

The team of scientists was selected by an expert review panel convened by the Mississippi-Alabama Sea Grant Consortium to conduct the independent study.

“American communities across the Gulf of Mexico depend on their access to, as well as the long term sustainability of, red snapper,” said U.S. Secretary of Commerce Wilbur Ross. “I look forward to the insights this project will provide as we study and manage this valuable resource.”

Recreational anglers and commercial fishers will play a key role
The research team, made up of 21 scientists from 12 institutions of higher learning, a state agency and a federal agency, was awarded $9.5 million in federal funds for the project through a competitive research grant process. With matching funds from the universities, the project will total $12 million.

“We’ve assembled some of the best red snapper scientists around for this study,” said Greg Stunz, the project leader and a professor at the Harte Research Institute for Gulf of Mexico Studies at Texas A&M University – Corpus Christi. “The team members assembled through this process are ready to address this challenging research question. There are lots of constituents who want an independent abundance estimate that will be anxiously awaiting our findings.”

Recreational anglers and commercial fishers will be invited to play a key role in collecting data by tagging fish, reporting tags and working directly with scientists onboard their vessels.

“The local knowledge fishermen bring to this process is very valuable and meaningfully informs our study,” Stunz said.

Some stakeholder groups have expressed concerns that there are more red snapper in the Gulf than currently accounted for in the stock assessment. The team of scientists on this project will spend two years studying the issue.

In 2016, Congress directed the National Sea Grant College Program and NOAA Fisheries to fund independent red snapper data collections, surveys and assessments, including the use of tagging and advanced sampling technologies. Sea Grant and NOAA Fisheries worked collaboratively to transfer federal funds to Mississippi-Alabama Sea Grant to administer the competitive research grant process and manage this independent abundance estimate.

“Today’s announcement is welcome news for all red snapper anglers in the Gulf of Mexico,” said Sen. Richard Shelby of Alabama. “As Chairman of the U.S. Senate Appropriations Subcommittee on Commerce, Justice, Science and Related Agencies, I was proud to author and secure federal funding to address the need for better data, which is a fundamental issue plaguing the fishery. The management of red snapper must be grounded in sound science if we want to provide fair access and more days on the water for our anglers. It is my hope that these independent scientists will be able to accurately determine the abundance of red snapper in the Gulf of Mexico once and for all.”

Project team will determine abundance and distribution of red snapper
The research will be driven largely by university-based scientists with partners from state and federal agencies, Stunz said.

The funding will allow the scientists to carry out an abundance estimate using multiple sampling methods with a focus on advanced technologies and tagging for various habitat types, he said.

“I’m pleased to see that the independent estimate is moving forward and including the expertise of recreational fishermen,” said Rep. John Culberson of Texas. “I will continue to work with Texas fishermen and NOAA to address the inadequate access to red snapper.”

The project team will determine abundance and distribution of red snapper on artificial, natural and unknown bottom habitat across the northern Gulf of Mexico.

As a statistician chosen for the team, SMU’s Stokes is also an expert in non-sampling survey errors, such as errors by interviewers and respondents. She recently conducted research on evaluating the accuracy of contest judges and on improving estimates of marine fishery yields by the National Oceanic and Atmospheric Administration.

Stokes also contributes to the National Assessment of Educational Progress, or “Nation’s Report Card,” examining the way schools and students are selected for the large study.

Besides SMU, others on the team include Texas A&M University, University of Florida, University of South Alabama, Louisiana State University, Florida International University, NOAA Fisheries, Auburn University, Mississippi State University, Louisiana Department of Wildlife and Fisheries, College of William and Mary, University of Southern Mississippi, and the University of South Florida. — Mississippi-Alabama Sea Grant and Southern Methodist University

Categories
Earth & Climate Fossils & Ruins Plants & Animals Student researchers Subfeature

Prehistoric puzzle settled: carbon dioxide link to global warming 22 million years ago

The modern link between high carbon dioxide levels and climate change didn’t appear to hold true for a time interval about 22 million years ago; but now a new study has found the link does indeed exist.

Fossil leaves from Africa have resolved a prehistoric climate puzzle — and also confirm the link between carbon dioxide in the atmosphere and global warming.

Research until now has produced a variety of results and conflicting data that have cast doubt on the link between high carbon dioxide levels and climate change for a time interval about 22 million years ago.

But a new study has found the link does indeed exist for that prehistoric time period, say researchers at Southern Methodist University, Dallas.

The finding will help scientists understand how recent and future increases in the concentration of atmospheric carbon dioxide may impact the future of our planet, say the SMU researchers.

The discovery comes from new biochemical analyses of fossil leaves from plants that grew on Earth 27 million years ago and 22 million years ago, said geologist Tekie Tesfamichael, lead scientist on the research.

The new analyses confirm research about modern climate — that global temperatures rise and fall with increases and decreases in carbon dioxide in our atmosphere — but in this case even in prehistoric times, according to the SMU-led international research team.

Carbon dioxide is a gas that is normally present in the Earth’s atmosphere, even millions of years ago. It’s dubbed a greenhouse gas because greater concentrations cause the overall temperature of Earth’s atmosphere to rise, as happens in a greenhouse with lots of sunlight.

Recently greenhouse gas increases have caused global warming, which is melting glaciers, sparking extreme weather variability and causing sea levels to rise.

The new SMU discovery that carbon dioxide behaved in the same manner millions of years ago that it does today has significant implications for the future. The finding suggests the pairing of carbon dioxide and global warming that is seen today also holds true for the future if carbon dioxide levels continue to rise as they have been, said Tesfamichael.

“The more we understand about the relationship between atmospheric carbon dioxide concentrations and global temperature in the past, the more we can plan for changes ahead,” said Tesfamichael, an SMU postdoctoral fellow in Earth Sciences.

“Previous work reported a variety of results and conflicting data about carbon dioxide concentrations at the two intervals of time that we studied,” he said. “But tighter control on the age of our fossils helped us to address whether or not atmospheric carbon dioxide concentration corresponded to warming — which itself is independently well-documented in geochemical studies of marine fossils in ocean sediments.”

The researchers reported their findings in Geology, the scientific journal of the Geological Society of America. The article is “Settling the issue of ‘decoupling’ between atmospheric carbon dioxide and global temperature: [CO2]atm reconstructions across the warming Paleogene-Neogene divide.”

Co-authors from the Roy M. Huffington Department of Earth Sciences in Dedman College are professors Bonnie Jacobs, an expert in paleobotany and paleoclimate, and Neil J. Tabor, an expert in sedimentology and sedimentary geochemistry.

Other co-authors are Lauren Michel, Tennessee Technological University; Ellen Currano, University of Wyoming; Mulugeta Feseha, Addis Ababa University; Richard Barclay, Smithsonian Institution; John Kappelman, University of Texas; and Mark Schmitz, Boise State University.

Discovery of rare, well-preserved fossil leaves enables finding
The findings were possible thanks to the rare discovery of two sites with extraordinarily well-preserved fossil leaves of flowering plants from the Ethiopian Highlands of eastern Africa.

Such well-preserved fossil leaves are a rarity, Tesfamichael said.

“Finding two sites with great preservation in the same geographic region from two important time intervals was very fortunate, as this enabled us to address the question we had about the relationship between atmospheric carbon dioxide concentration and global temperatures,” he said.

Scientists know that variations in the concentration of atmospheric carbon dioxide affect carbon fixation in leaves during photosynthesis. This causes leaves to develop anatomical and physiological changes such as the frequency and size of stomata — the pores on the surface of a leaf through which carbon passes.

Scientists can measure those attributes, among others, in fossil leaves, so that leaf fossils can be used as proxies for Earth’s atmospheric carbon dioxide history.

The sites producing the leaves for the SMU study were discovered separately in years past, but major fossil collections were produced through field work coordinated by the SMU research team and their co-authors, who have been collaborating on this project for several years.

The work has had funding from the National Science Foundation, The National Geographic Committee for Research and Exploration, the SMU Ford Fellowship Program, SMU Research Council, the Institute for the Study of Earth and Man, and the Dallas Paleontological Society Frank Crane Scholarship.

The fossils are housed permanently in the collections at the National Museum of Ethiopia in Addis Ababa. Institutional and governmental support came from the National Museum of Ethiopia, the Authority for Research and Conservation of Cultural Heritage, and Addis Ababa University.

Previous studies firmly established a temperature difference
One of the sites dates to the late Oligocene Epoch, and the other to the early Miocene.

Previous studies that measured ocean temperatures from around the world for the two intervals have firmly established a temperature difference on Earth between the two times, with one much warmer than the other. So the SMU study sought to measure the levels of carbon dioxide for the two time periods.

For the SMU analyses, fossil leaves of a single species were collected from the 27 million-year-old late Oligocene site. The leaves had been deposited during prehistoric times in the area of Chilga in northwest Ethiopia most likely at a river bank. The Earth’s climate during the late Oligocene may have been somewhat warmer than today, although glaciers were forming on Antarctica. The SMU study found carbon dioxide levels, on average, around 390 parts per million, about what it is on Earth today.

Fossil leaves of the 22 million-year-old species from the early Miocene were collected from ancient lake deposits, now a rock called shale, from the modern-day Mush Valley in central Ethiopia. The early Miocene climate at that time was warmer than the late Oligocene and likewise the SMU study found higher carbon dioxide levels. Atmospheric carbon dioxide was about 870 parts per million, double what it is on Earth today.

The SMU study confirmed a relationship between carbon dioxide and temperature during the late Oligocene and early Miocene.

Paleoclimate data can help predict our planet’s future climate
While carbon dioxide isn’t the only factor affecting Earth’s climate or global mean temperature, it is widely considered by scientists among the most significant. Much is known about climate change and global warming, but questions still remain.

“One of those is ‘What’s the sensitivity of the Earth’s temperature to carbon dioxide concentration? Is it very sensitive? Is it not so sensitive?’ Estimating temperature and carbon dioxide concentrations for times in the past can help find the answer to that question,” Jacobs said. “There’s a lot of work on paleoclimate in general, but not as much on the relationship between carbon dioxide and temperature.”

The finding is an important one.

“The amount of temperature change during this interval is approximately within the range of the temperature change that is estimated from climate models for our next century given a doubling of carbon dioxide concentration since the industrial revolution,” Jacobs said.

With the new model reaffirming the prehistoric relationship, scientists can look now at related questions, said climate change scientist Lauren Michel, who worked on the study as a post-doctoral researcher at SMU.

“Answering questions about the rate of change and which factors changed first, for example, will ultimately give a clearer picture of the Earth’s climate change patterns,” Michel said. “I think it is valuable to understand the relationship of greenhouse gases and climate factors represented in the rock record so we can have a better idea of what we can expect in the future and how we can prepare for that.”

SMU study confirms relationship that previous methods overlooked
Previous studies found little to no correlation between temperature and carbon dioxide for the late Oligocene and early Miocene. That has puzzled paleoclimate researchers for at least a decade.

“We have a good test-case scenario with these well-preserved plants from both time slices, where we know one time slice, with higher levels of carbon dioxide, was a warmer climate globally than the other,” Tesfamichael said.

“It’s been a puzzle as to why the previous methods found no relationship, or an inverse correlation,” he said. “We think it’s for lack of the well-dated proxy — such as our fossil leaves from two precise times in the same region — which deliver a reliable answer. Or, perhaps the models themselves needed improvement.”

Previous studies used methodologies that differed from the SMU study, although all methods (proxies) incorporate some aspects of what is known about living organisms and how they interact with atmospheric carbon dioxide.

Some studies rely on biochemical modeling of the relationship between single-celled marine fossils and atmospheric carbon dioxide, and others rely on the relationship between stomata and atmospheric carbon dioxide concentration observed in the living relatives of particular fossil plant species.

“Each method has its assumptions,” said Tesfamichael. “We will see if our results hold up with further studies of this time interval using the same methodology we used.” — Margaret Allen, SMU

Categories
Earth & Climate Fossils & Ruins Plants & Animals Researcher news SMU In The News

Australian Geographic: Secrets of leaf size revealed

New findings reveal the real reasons behind varying leaf sizes.

Australian Geographic has covered the research of SMU paleobotanist Bonnie F. Jacobs, a professor in SMU’s Roy M. Huffington Department of Earth Sciences.

Working with a global team of researchers, Jacobs and her colleagues cracked the mystery of leaf size. The research was published Sept. 1, 2017 as a cover story in Science.

The researchers from Australia, the U.K., Canada, Argentina, the United States, Estonia, Spain and China analyzed leaves from more than 7,600 species of plants over the past 20 years, then pooled and analyzed the data with new theory to create a series of equations that can predict the maximum viable leaf size anywhere in the world based on the risk of daytime overheating and night-time freezing.

The researchers will use these findings to create more accurate vegetation models. This will be used by governments to predict how vegetation will change locally and globally under climate change, and to plan for adaptation.

Jacobs contributed an extensive leaf database — research that was funded by a National Science Foundation grant. She analyzed the leaf characteristics of 880 species of modern tropical African plants, which occurred in various combinations among 30 plant communities. Jacobs measured leaves of the plant specimens at the Missouri Botanical Garden Herbarium, one of the largest archives of pressed dried plant specimens from around the world.

Jacobs is one of a handful of the world’s experts on the fossil plants of ancient Africa. As part of a team of paleontologists working there, she hunts plant and animal fossils in Ethiopia’s prolific Mush Valley, as well as elsewhere in Africa.

Read the full story.

EXCERPT:

By Karl Gruber
Australian Geographic

You may have learnt at school that leaf size depends on water availability and that they are meant to help plants avoid overheating. But a new study that looked at leaf sizes around the world found that, rather than water availability, it all boils down to temperature, both high and low.

Leaf sizes can vary by as much as 100,000 fold, with some leaves having an area of just 1 mm2 while other can have an area of up to 1 m2. But what is driving these big differences?

“The conventional explanation was that water availability and overheating were the two major limits to leaf size. But the data didn’t fit,” says Ian. “For example the tropics are both wet and hot, and leaves in cooler parts of the world are unlikely to overheat,” explained Ian Wright, from Macquarie University, who led the new study.

A key finding from the study is that for plants all around the world the main factors limiting leaf size are the risk of frosting in cold nights, which can damage leaves, and the risk of overheating during the day.

“Latitude explains 28% of variation leaf size, globally. Warm wet regions are characterised by large-leaved species, warm dry regions and cold regions by smaller-leaved species. These patterns can all be understood in relation to the energy inputs and outputs to leaves, but only if you consider both the daytime (overheating) and night-time (freezing) risks,” Wright says.

Read the full story.