Scientists led by UCL (University College London) found that crocodiles and their ancient relatives spent much of their 250 million years of evolutionary history following warm climates rather than adapting to dramatically different temperatures. When Earth grew hotter, they expanded into new regions, sometimes reaching as far as Antarctica. As temperatures fell, they moved back toward the tropics.

Published in Science Advances, the study analyzed more than 7,000 fossils and records from over 400 living and extinct species. Researchers combined this evidence with computer models that reconstructed Earth’s climate and geography across 245 million years.

The results suggest that tropical and subtropical regions remained suitable for crocodile relatives after the asteroid struck, even as the environments available to many dinosaurs deteriorated. Only the most extreme climate simulations eliminated these potential refuges.

Why Crocodiles Survived the Dinosaur Extinction

The researchers examined how conditions on Earth may have changed following the asteroid impact 66 million years ago. Their simulations indicated that areas near the equator could have remained warm enough to support crocodile relatives, providing places where surviving populations could persist and eventually recover.

Previous modeling by members of the same research team found that suitable habitats for non-avian dinosaurs (i.e., the ones that went extinct) contracted much more severely after the impact.

Lead author Dr. Alfio Alessandro Chiarenza, based at UCL Earth Sciences, said: “The asteroid did not make the whole planet equally hostile to every group.

“Crocodiles’ long-standing preference for warm environments may have placed survivors exactly where suitable climates held up best, like around the equator. These refuges could have sheltered populations that later recovered and radiated out.”

The discovery offers a possible explanation for how a group of animals that appeared around the same time as dinosaurs managed to endure two of Earth’s five major mass extinctions.

Ancient Crocodiles Were Far More Diverse

Modern crocodiles and their close relatives share many recognizable features, but their evolutionary history reveals a much wider variety of body shapes, sizes, and lifestyles.

The broader crocodile lineage, known as pseudosuchians, once included heavily armored plant eaters, predators that hunted entirely on land, and enormous animals weighing more than a metric ton.

Among the most remarkable was Sarcosuchus, a giant predator nicknamed the “super croc” that could reach 12 meters in length. Another prehistoric relative, Postosuchus, was a land dwelling hunter capable of moving on either two legs or all four.

Dr. Chiarenza said: “Crocodiles are often called living fossils, but their ancestors and relatives changed enormously throughout their history, ranging from giants the size of a bus that could have devoured a T. rex, to small, cute animals with the face of a pug.

“Our study shows that, despite all this diversity, what stayed surprisingly consistent was their relationship with climate.”

Fossils Reveal 245 Million Years of Climate History

To investigate that relationship, the scientists reconstructed the temperature and rainfall preferences of 400 crocodile species and their ancient relatives. They used fossil evidence, evolutionary family trees, and detailed maps of where living crocodile species are found today.

The team then compared these preferences with reconstructions of ancient geography and climate to identify where suitable habitats existed at different points in Earth’s history.

A clear pattern emerged. Crocodile relatives generally followed warmer conditions as the planet’s climate changed, expanding their ranges during hot periods and retreating when temperatures cooled.

About 50 million years ago, during the particularly warm early Eocene, global temperatures were approximately 10°C higher than today, and the polar regions had no permanent ice. Crocodile relatives lived at high latitudes across North America, Europe, and even Antarctica.

Over the following millions of years, global cooling gradually reduced the areas where they could thrive. Their geographic range contracted toward warmer tropical regions.

Two Surprising Exceptions

Although this preference for warm environments remained remarkably consistent, the researchers identified two important exceptions.

During the Cretaceous Thermal Maximum, approximately 94 million years ago, global temperatures climbed as much as 14°C above modern levels. One branch of the crocodile family tree evolved the ability to tolerate hotter conditions than the broader lineage could withstand at other times.

A separate adaptation occurred around 34 million years ago in Australia. As a prolonged cooling period reduced rainfall and dried out the continent, an extinct group of crocodiles adapted to increasingly arid, desert-like environments.

These exceptions show that some crocodile relatives could evolve to handle different climates, even though most continued to follow their preferred warm conditions.

What Happened After the Dinosaur-Killing Asteroid?

The researchers also used climate simulations to investigate the decades and centuries immediately following the Chicxulub asteroid impact, which triggered the extinction of most dinosaurs.

They explored several possible environmental consequences, including sunlight being blocked by dust and ash and rising carbon dioxide levels associated with volcanic eruptions.

When the simulations reduced sunlight by 5% or 10%, warm regions near the equator remained suitable for crocodile relatives. These areas could have provided critical refuges during the environmental disruption.

However, a more severe scenario involving a 15% reduction in sunlight left those regions unsuitable as well. The researchers noted that this extreme level of reduced sunlight is now considered unlikely.

Other simulated changes, including increased atmospheric carbon dioxide, did not alter the availability of suitable climates for crocodiles.

Together, the results suggest that crocodiles may have benefited from living in regions where temperatures remained within their preferred range, even as conditions became much less favorable for many dinosaurs.

The Survival Strategy That Could Now Become a Weakness

The researchers emphasized that favorable temperatures were probably only one reason crocodiles survived the mass extinction.

Other characteristics likely improved their chances, including relatively small body sizes, the ability to live partly in water, flexible diets, and modest energy requirements. As ectothermic (“cold-blooded”) animals, crocodiles need less food to maintain their bodies than many animals that generate their own body heat.

The findings also raise important questions about how crocodiles will respond to modern climate change.

For millions of years, moving into regions with suitable temperatures appears to have been one of their main responses to a changing planet. Today, however, expanding cities, agricultural land, and roads increasingly limit where wildlife can move.

Professor Philip Mannion, based at UCL Earth Sciences, said: “These findings have implications for species today. If crocodiles mostly coped with past climate change by moving towards suitable habitats, today’s species will need room to move as the planet warms, and the loss of suitable areas to roads, farms and cities is making that harder.”

The research was funded by The Royal Society, the Leverhulme Trust, and the National Environment Research Council (NERC).

That challenge extends far beyond maps. Similar calculations are important for transportation systems, communication networks, and even biological structures involving proteins, neurons, or other interconnected components. As these networks grow, determining the shortest routes between all their points becomes increasingly difficult.

Computer scientists call this the All-Pairs Shortest Paths (APSP) problem. It involves finding the shortest distance between every pair of points in a graph. In this context, a ‘graph’ is simply a collection of points (called vertices) joined by connections (called edges). Those points might represent cities, PCs, subway stations, or organs, while the connections could stand for highways, cables, railway lines, or blood vessels.

Why Calculating Shortest Paths Is So Difficult

Determining the exact shortest distances across a massive network can consume enormous amounts of computing time and memory. In densely connected networks, some conventional approaches require what mathematicians call cubic time. That means doubling the number of points can increase the computational workload by roughly eight times.

Because the required computation (work) can grow much faster than the network itself, researchers have spent decades searching for more efficient methods. One promising solution is to use approximation algorithms, which calculate estimates rather than exact answers. The goal is to produce distances that are sufficiently accurate while dramatically reducing the amount of computation required.

An important advance came in 1996, when researchers Dor, Halperin, and Zwick (DHZ) developed a method capable of producing distance estimates within twice the actual shortest distance for sufficiently distant points, while operating in nearly optimal time.

This level of accuracy is known as a “2‑approximation.” For example, if the shortest possible route between two locations is 10 kilometers, an estimate satisfying this guarantee would fall between 10 and 20 kilometers.

Rather than examining every possible route, the DHZ approach uses a relatively small selection of points from the network (referred to as sampled vertices). These strategically selected points serve as shortcuts that help the algorithm estimate distances more efficiently.

A Clever Shortcut With a Hidden Weakness

The approach works particularly well when the points being compared are far apart.

Consider a journey between Delhi and Chennai. Because the cities are separated by a considerable distance, the algorithm can often find a sampled point close to the shortest route. This allows it to calculate an estimate that remains within the promised limit of twice the actual distance.

However, the same strategy becomes less dependable when the two points are close together.

Imagine calculating the shortest route between two neighborhoods in the Mumbai suburbs. The sampled points might be located too far from the most direct connection, forcing the algorithm to estimate a much longer route.

For example, two points might be connected by a path containing just two edges, yet the sampled route could contain five. Because five exceeds twice the true distance of two, the result violates the “at most twice” accuracy guarantee.

This weakness meant that the original algorithm’s mathematical guarantee applied only when the points were sufficiently far apart. For closer connections, the same level of accuracy could not always be assured.

That limitation remained a challenge for nearly three decades.

A New Algorithm Breaks Through a Decades-Old Limit

Now, Dr. Manoj Gupta, an Associate Professor at the Indian Institute of Technology Gandhinagar, has introduced a refinement that extends the accuracy guarantee to points much closer together than earlier methods allowed.

Gupta presented his research at the 66th Annual Symposium on Foundations of Computer Science (FOCS 2025) in a paper titled “Improved 2-Approximate Shortest Paths for close vertex pairs.”

The achievement is particularly significant because the improved algorithm preserves the overall runtime of the earlier approach while expanding the range of distances for which reliable estimates can be guaranteed.

The breakthrough comes from rethinking how points are sampled within the network.

Traditional methods depended on a collection of representative points to estimate distances. Gupta’s approach instead introduces a multi-scale sampling strategy that organizes information about the network at several different levels.

By analyzing connections at multiple scales rather than relying on a single sampling layer, the algorithm can account for shorter routes that previous approaches might overlook.

This more sophisticated sampling technique reduces the minimum distance required for the 2-approximation guarantee to hold, without increasing the algorithm’s overall computational complexity.

Returning to the transportation example, the original DHZ method could efficiently estimate sufficiently long journeys, such as the route between Delhi and Chennai. The improved approach extends that dependable accuracy to much shorter connections (such as Mumbai’s suburbs).

The central achievement is not simply a new way to estimate distances. It is the ability to provide the same mathematical accuracy guarantee across a wider range of distances while maintaining computational efficiency.

Why This Computer Science Breakthrough Matters

Massive networks are fundamental to modern technology. Internet infrastructure, transportation systems, social media platforms, and artificial intelligence applications all depend on analyzing complicated webs of interconnected information.

In many situations, obtaining a perfectly exact distance is less important than producing a dependable estimate quickly. When networks contain enormous numbers of connections, the ability to balance accuracy and speed becomes especially valuable.

Gupta’s research strengthens the mathematical foundations of algorithms designed to handle these challenges. Although the findings are theoretical and do not establish immediate improvements to specific commercial systems, they offer a better way to approach distance calculations in large networks.

The work also provides insight into how the overall structure of a network can be understood through carefully selected local connections. By improving how these relationships are sampled and analyzed, researchers can move closer to efficiently estimating distances between every pair of points in a massive system.

Progress in theoretical computer science often comes through incremental refinements rather than dramatic changes. Improving an influential result that dates back to 1996 therefore represents a meaningful advance.

By extending a longstanding accuracy guarantee without increasing overall runtime, the new algorithm pushes beyond an important mathematical boundary and strengthens the techniques underlying some of today’s most complex connected systems.

During the spacewalk, Menon and Kutryk installed and deployed a new International Space Station Roll-Out Solar Array (IROSA) on the station’s 2A electrical power channel. This is the seventh such array added to the station, providing additional electricity for essential operations, including the station’s eventual safe and controlled deorbit.

Final Spacewalk Will Complete Solar Array Upgrade

The astronauts also performed several preliminary tasks to prepare for another spacewalk scheduled for Thursday, Nov. 5. During that mission, astronauts will install the eighth and final solar array on the station’s 3B power channel. NASA plans to begin live coverage at 6:45 a.m., with information on how to watch available through the agency.

Once the final array is installed, the International Space Station’s solar power expansion will be complete. Together, the eight new arrays will increase the station’s available power by as much as 30%, raising its electricity generation capacity from 160 kilowatts to approximately 215 kilowatts.

A Milestone for Space Station Operations

The completed mission, designated U.S. spacewalk 100, marked Menon’s fourth spacewalk and Kutryk’s first. It was also the 285th spacewalk conducted to support the assembly, maintenance, and improvement of the International Space Station.

A study published in Neurology, the medical journal of the American Academy of Neurology, found that people who consumed the most low- and no-calorie sweeteners experienced significantly faster declines in memory and thinking skills than those who consumed the least. The association was particularly pronounced among people with diabetes.

Researchers examined seven sweeteners commonly used in foods and beverages: aspartame, saccharin, acesulfame-K, erythritol, xylitol, sorbitol and tagatose. These ingredients frequently appear in ultra-processed products, including diet sodas, flavored waters, energy drinks, yogurt and low-calorie desserts. Some are also sold separately for sweetening foods and beverages.

“Low- and no-calorie sweeteners are often seen as a healthy alternative to sugar; however, our findings suggest certain sweeteners may have negative effects on brain health over time,” said study author Claudia Kimie Suemoto, MD, PhD, of the University of São Paulo in Brazil.

Importantly, the findings show an association rather than a proven cause-and-effect relationship. Researchers cannot conclude from this study that consuming these sweeteners directly damages the brain or causes memory loss.

Study Tracks Nearly 13,000 Adults for Eight Years

To investigate whether sugar substitutes might be connected to cognitive health, researchers analyzed data from 12,772 adults across Brazil. Participants were 52 years old on average when the study began and were followed for approximately eight years.

At the beginning of the study, participants completed detailed dietary questionnaires describing the foods and drinks they had consumed during the previous year. Researchers used these responses to estimate each person’s daily intake of the seven sweeteners.

Participants were then separated into three groups according to how much of the sweeteners they consumed. Those in the lowest consumption group averaged 20 milligrams per day (mg/day), while those in the highest group averaged 191 mg/day. For comparison, 191 milligrams of aspartame is roughly the amount found in one can of diet soda.

Of the seven sweeteners examined, sorbitol had the highest average intake, at 64 mg/day. Sorbitol belongs to a category of sweeteners called sugar alcohols, which provide sweetness and are commonly used as sugar substitutes.

Throughout the study, participants completed cognitive assessments at three points: the beginning, middle, and end. These tests measured several abilities essential for everyday mental functioning, including memory, language, and the speed at which the brain processes information.

Researchers evaluated verbal fluency, or the ability to quickly retrieve and produce words, along with working memory, which allows people to temporarily hold and use information. They also tested word recall and processing speed to determine how these abilities changed over time.

High Sweetener Consumption Linked to 62% Faster Cognitive Decline

The results revealed a striking difference between people who consumed the most sweeteners and those who consumed the least.

After accounting for factors that could influence cognitive health, including age, sex, high blood pressure, and cardiovascular disease, researchers found that participants in the highest consumption group experienced a 62% faster decline in overall thinking and memory abilities compared with those in the lowest group.

That difference was equivalent to approximately 1.6 additional years of cognitive aging over the study period.

Even moderate consumption was associated with measurable differences. Participants in the middle group experienced a 35% faster decline than those consuming the least, equivalent to roughly 1.3 additional years of cognitive aging.

These estimates describe changes in cognitive test performance rather than a direct measurement of biological brain aging. They also do not mean that everyone who consumes artificial sweeteners will experience memory problems.

Stronger Links Found in Adults Under 60 and People With Diabetes

When researchers examined different age groups, they discovered that the association was not consistent across all participants.

Among adults younger than 60, higher sweetener consumption was linked to faster declines in verbal fluency and overall cognitive performance. However, researchers did not find a similar association among participants older than 60.

The relationship was also stronger in people with diabetes than in those without the condition. This finding is especially relevant because people with diabetes frequently turn to sugar substitutes to help manage their sugar intake.

Examining the sweeteners individually revealed another important distinction. Six of the seven substances were associated with faster declines in overall cognitive performance, particularly memory.

Those six were aspartame, saccharin, acesulfame-K, erythritol, sorbitol and xylitol.

Tagatose was the exception. Researchers found no association between its consumption and cognitive decline in this study. However, that finding does not establish that tagatose protects the brain or is necessarily safer than other sweeteners.

Should People Rethink Artificial Sweeteners?

The findings raise important questions about whether replacing sugar with low-calorie alternatives always delivers the health benefits consumers expect, particularly when it comes to the brain.

“While we found links to cognitive decline for middle-aged people both with and without diabetes, people with diabetes are more likely to use artificial sweeteners as sugar substitutes,” Suemoto said. “More research is needed to confirm our findings and to investigate if other refined sugar alternatives, such as applesauce, honey, maple syrup or coconut sugar, may be effective alternatives.”

Researchers also acknowledged several limitations. The analysis did not cover every artificial sweetener available on the market, so the findings cannot necessarily be applied to all sugar substitutes.

In addition, dietary information came from participants’ own recollections of what they had eaten and drunk. Because people may forget foods, underestimate portions, or inaccurately report their habits, these estimates may not perfectly reflect actual sweetener consumption.

The observational design also means that other factors could help explain the relationship between sweetener intake and cognitive decline, despite researchers’ efforts to account for several important health differences.

Further studies will be needed to determine whether the sweeteners themselves contribute to changes in brain function, why certain groups appear more strongly affected, and whether different sugar alternatives produce different long-term outcomes.

The research was supported by the Brazilian Ministry of Health, the Ministry of Science, Technology, and Innovation, and the National Council for Scientific and Technological Development.