From Duke University (US) : “The Climate-Driven Mass Extinction No One Had Seen”


From Duke University (US)

October 7, 2021
Marie Claire Chelini

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Fossils of the key groups used to unveil the Eocene-Oligocene extinction in Africa with primates on the left, the carnivorous hyaenodont, upper right, rodent, lower right. These fossils are from the Fayum Depression in Egypt. (Matt Borths)

Sixty-three percent. That’s the proportion of mammal species that vanished from Africa and the Arabian Peninsula around 30 million years ago, after Earth’s climate shifted from swampy to icy. But we are only finding out about it now.

Compiling decades of work, a new study published this week in the journal Communications Biology reports on a previously undocumented extinction event that followed the transition between the geological periods called the Eocene and Oligocene.

That time period was marked by dramatic climate change. In a reverse image of what is happening today, the Earth grew cooler, ice sheets expanded, sea levels dropped, forests started changing to grasslands and carbon dioxide became scarce. Nearly two-thirds of the species known in Europe and Asia at that time went extinct.

African mammals were thought to have possibly escaped unscathed. Africa’s mild climate and proximity to the Equator could have been a buffer from the worst of that period’s cooling trend.

Now, thanks in great part to a large collection of fossils housed at the Duke Lemur Center Division of Fossil Primates (DLCDFP), researchers have shown that, despite their relatively balmy environment, African mammals were just as affected as those from Europe and Asia. The collection was the life’s work of the late Elwyn Simons of Duke, who scoured Egyptian deserts for fossils for decades.

The team, comprising researchers from the United States, England, and Egypt, looked at fossils of five mammal groups: a group of extinct carnivores called hyaenodonts, two rodent groups, the anomalures (scaly-tail squirrels) and the hystricognaths (a group that includes porcupines and naked mole rats), and two primate groups, the strepsirrhines (lemurs and lorises), and our very own ancestors, the anthropoids (apes and monkeys).

By gathering data on hundreds of fossils from multiple sites in Africa, the team was able to build evolutionary trees for these groups, pinpointing when new lineages branched out and time-stamping each species’ first and last known appearances.

Their results show that all five mammal groups suffered huge losses around the Eocene-Oligocene boundary.

“It was a real reset button,” said Dorien de Vries, a postdoctoral researcher at The University of Salford (UK) and lead author of the paper.

After a few million years, these groups start popping up again in the fossil record, but with a new look. The fossil species that re-appear later in the Oligocene, after the big extinction event, are not the same as those that were found before.

“It’s very clear that there was a huge extinction event, and then a recovery period,” said Steven Heritage, Researcher and Digital Preparator at Duke University’s DLCDFP and coauthor of the paper.

The evidence is in these animals’ teeth. Molar teeth can tell a lot about what a mammal eats, which in turns tells a lot about their environment.

The rodents and primates that reappeared after a few million years had different teeth. These were new species, who ate different things, and had different habitats.

“We see a huge loss in tooth diversity, and then a recovery period with new dental shapes and new adaptations,” said de Vries.

“Extinction is interesting in that way,” said Matt Borths, curator of Duke University’s DLCDFP and coauthor of the paper. “It kills things, but it also opens up new ecological opportunities for the lineages that survive into this new world.”

This decline in diversity followed by a recovery confirms that the Eocene-Oligocene boundary acted as an evolutionary bottleneck: most lineages went extinct, but a few survived. Over the next several millions of years, these surviving lines diversified.

“In our anthropoid ancestors, diversity bottoms out to almost nothing around 30 million years ago, leaving them with a single tooth type,” said Erik R. Seiffert, Professor and Chair of the Department of Integrative Anatomical Sciences at the Keck School of Medicine of the University of Southern California, a former graduate student of Simons, and senior coauthor of the paper. “That ancestral tooth shape determined what was possible in terms of later dietary diversification.”

“There’s an interesting story about the role of that bottleneck in our own early evolutionary history,” said Seiffert. “We came pretty close to never existing, if our monkey-like ancestors had gone extinct 30 million years ago. Luckily they didn’t.”

A rapidly changing climate wasn’t the only challenge facing these few surviving types of mammals. As temperatures dropped, East Africa was pummeled by a series of major geological events, such as volcanic super eruptions and flood basalts – enormous eruptions that covered vast expanses with molten rock. It was also at that time that the Arabian Peninsula separated from East Africa, opening the Red Sea and the Gulf of Aden.

“We lost a lot of diversity at the Eocene-Oligocene boundary,” said Borths. “But the species that survived apparently had enough of a toolkit to persist through this fluctuating climate.”

“Climate changes through geological time have shaped the evolutionary tree of life,” said Hesham Sallam, founder of The Mansoura University [جامعة المنصورة](EG) Vertebrate Paleontology Center in Egypt and coauthor of the paper. “Collecting evidence from the past is the easiest way to learn about how climate change will affect ecological systems.”

Funding for this study came from The Leakey Foundation, the U.S. National Science Foundation (BSC-1824745 to DD. and DBI-1612062 to MRB), and the Natural Environment Research Council (NERC NE/T000341/1). Field work in the Fayum Depression, Egypt, and digital curation of Fayum fossils were supported by the U.S. National Science Foundation (BCS-0416164, BCS-0819186, and BCS-1231288) as well as Gordon and Ann Getty and The Leakey Foundation. Micro-CT scanning was partially supported by NSF grant DBI-1458192, DBI-2023087, and IMLS grant MA-245704-OMS-20.

See the full article here .

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Younger than most other prestigious U.S. research universities, Duke University (US) consistently ranks among the very best. Duke’s graduate and professional schools — in business, divinity, engineering, the environment, law, medicine, nursing and public policy — are among the leaders in their fields. Duke’s home campus is situated on nearly 9,000 acres in Durham, N.C, a city of more than 200,000 people. Duke also is active internationally through the Duke-NUS Graduate Medical School in Singapore, Duke Kunshan University in China and numerous research and education programs across the globe. More than 75 percent of Duke students pursue service-learning opportunities in Durham and around the world through DukeEngage and other programs that advance the university’s mission of “knowledge in service to society.”

Duke University is a private research university in Durham, North Carolina. Founded by Methodists and Quakers in the present-day town of Trinity in 1838, the school moved to Durham in 1892. In 1924, tobacco and electric power industrialist James Buchanan Duke established The Duke Endowment and the institution changed its name to honor his deceased father, Washington Duke.

The campus spans over 8,600 acres (3,500 hectares) on three contiguous sub-campuses in Durham, and a marine lab in Beaufort. The West Campus—designed largely by architect Julian Abele, an African American architect who graduated first in his class at the University of Pennsylvania (US) School of Design—incorporates Gothic architecture with the 210-foot (64-meter) Duke Chapel at the campus’ center and highest point of elevation, is adjacent to the Medical Center. East Campus, 1.5 miles (2.4 kilometers) away, home to all first-years, contains Georgian-style architecture. The university administers two concurrent schools in Asia, Duke-NUS Medical School in Singapore (established in 2005) and Duke Kunshan University in Kunshan, China (established in 2013).

Duke is ranked among the top universities in the United States. The undergraduate admissions are among the most selective in the country, with an overall acceptance rate of 5.7% for the class of 2025. Duke spends more than $1 billion per year on research, making it one of the ten largest research universities in the United States. More than a dozen faculty regularly appear on annual lists of the world’s most-cited researchers. As of 2019, 15 Nobel laureates and 3 Turing Award winners have been affiliated with the university. Duke alumni also include 50 Rhodes Scholars, 25 Churchill Scholars, 13 Schwarzman Scholars, and 8 Mitchell Scholars. The university has produced the third highest number of Churchill Scholars of any university (behind Princeton University (US) and Harvard University (US)) and the fifth-highest number of Rhodes, Marshall, Truman, Goldwater, and Udall Scholars of any American university between 1986 and 2015. Duke is the alma mater of one president of the United States (Richard Nixon) and 14 living billionaires.

Duke is the second-largest private employer in North Carolina, with more than 39,000 employees. The university has been ranked as an excellent employer by several publications.

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Duke’s research expenditures in the 2018 fiscal year were $1.168 billion, the tenth largest in the U.S. In fiscal year 2019 Duke received $571 million in funding from the National Institutes of Health. Duke is classified among “R1: Doctoral Universities – Very high research activity”.

Throughout the school’s history, Duke researchers have made breakthroughs, including the biomedical engineering department’s development of the world’s first real-time, three-dimensional ultrasound diagnostic system and the first engineered blood vessels and stents. In 2015, Paul Modrich shared the Nobel Prize in Chemistry. In 2012, Robert Lefkowitz along with Brian Kobilka, who is also a former affiliate, shared the Nobel Prize in chemistry for their work on cell surface receptors. Duke has pioneered studies involving nonlinear dynamics, chaos, and complex systems in physics.

In May 2006 Duke researchers mapped the final human chromosome, which made world news as it marked the completion of the Human Genome Project. Reports of Duke researchers’ involvement in new AIDS vaccine research surfaced in June 2006. The biology department combines two historically strong programs in botany and zoology, while one of the divinity school’s leading theologians is Stanley Hauerwas, whom Time named “America’s Best Theologian” in 2001. The graduate program in literature boasts several internationally renowned figures, including Fredric Jameson, Michael Hardt, and Rey Chow, while philosophers Robert Brandon and Lakatos Award-winner Alexander Rosenberg contribute to Duke’s ranking as the nation’s best program in philosophy of biology, according to the Philosophical Gourmet Report.