In Chicago’s Field Museum, behind a series of access-controlled doors, are about 1,500 dinosaur fossil specimens. The palaeobiologist Jasmina Wiemann walks straight past the bleached leg bones – some as big as her – neither does she glance at the fully intact spinal cord, stained red by iron oxides filling the spaces where there was once organic material. She only has eyes for the deep chocolate-brown fossils: these are the ones containing preserved organic matter – bones that offer unprecedented insights into creatures that went extinct millions of years ago. Wiemann is part of the burgeoning field of conservation palaeobiology, where researchers are looking to the deep past to predict future extinction vulnerability. At a time when humans could be about to witness a sixth mass extinction, studying fossil records is particularly useful for understanding how the natural world responded to problems before we arrived: how life on Earth reacted to environmental change over time, how species adapted to planet-scale temperature changes, or what to expect when ocean geochemical cycles change. “This is not something that we can simulate in the laboratory or meaningfully observe right now in the present day,” Wiemann says. “We have to rely on the longest ongoing experiment.” To observe that planet-scale experiment, scientists have developed new methods of gathering information from the bones of the distant past. After collecting her fossils, Wiemann puts them under a microscope that shoots a laser at the specimen. She displays a section on her computer screen, 50 times its original size, and moves across the fossil’s surface until she finds a dark spot with a seemingly velvety surface – this is the fossilised organic matter. Wiemann turns the room lights off, a tiny dot of light beams on to the fossil, and a curved line starts appearing on the computer screen. Every compound reacts differently to the laser, and where the bumps in this line are appearing across her chart suggest she was successful at finding organics. “This is beautiful,” she says. She will need to run through the data later, but this should reveal whether the specimen under her microscope was warm or cold-blooded. Using this method, Wiemann studied when warm-bloodedness emerged around the Permian-Triassic mass extinction (the biggest in history) and the Cretaceous-Paleogene (when the dinosaurs went extinct). Warm-bloodedness was already established as a factor that made species less likely to go extinct, as they can regulate their internal temperature in changing climates. But Wiemann found a new result – that many animals evolved warm-bloodedness independently after each of these extinctions. This could have implications for how animals adapt and find resilience as the planet warms. “If we want to, in any way, even in the short term, make meaningful predictions, we have to demonstrate that we understand these processes,” she says. One of the first people to write about combining ecological and palaeontological approaches to predict extinction vulnerability was Michael McKinney, now the director of environmental studies at the University of Tennessee. After graduating with a degree in palaeontology he began working but says he kept feeling a need to be more relevant. “I love the dinosaurs, the big picture,” he says. “But I kept thinking that it gives us a great context, but it wasn’t teaching me a lot that I could apply directly to the immediate problems.” McKinney went on to create his current department, which merges geology and ecology. Now, he sees palaeobiology as useful to predict what will happen. But understanding what to do about it is more difficult. “If you think about what the world’s going to be like 1,000 years from now, I think deep time can help us answer that question,” he says. “But if I’m worried about the fact that the Amazon rainforest is disappearing in the next 20 years, I’m sceptical deep time can inform that.” Humans, he says, have found new ways of driving species to extinction, from the passenger pigeon to the dodo. “We operate by rules that don’t really apply to the past. The things that we do are so fast and so unpredictable.” But deep time can offer insights into how species respond to very large, systemic changes – such as the temperature shifts we are now seeing. Erin Saupe, a professor of palaeobiology at the University of Oxford, uses large datasets to look at patterns of extinction in the fossil record to see which traits make species most vulnerable. In a recent paper published in Science, she and her co-authors asked whether intrinsic traits, including body size and geographic range size, were more or less important in predicting extinction than external factors such as climate change. “Nobody has looked at this question before,” Saupe says. Previous research has shown larger animals are typically less likely to go extinct in marine environments but are more prone to extinction on land, and larger “range sizes” – the distance a species is distributed over – help species avoid extinction. The team accessed a digital database to look at 290,000 marine invertebrate fossils from across the past 485m years, and used models to reconstruct the climate over that period. They found geographic range size was the most important predictor of extinction, perhaps because of its interconnection with other factors associated with a lower extinction risk. A large range size suggests the animal is also good at moving larger distances, and if a species is widely spread, a regional climate change in one area likely wouldn’t impact all populations. The team found all intrinsic traits they looked at, as well as climate change, were important in predicting extinction. “Even if a species has traits that usually make them resistant to climate change and to extinction, if the magnitude of climate change is large enough, they will still go extinct,” Saupe says. “I think it’s quite an important message for the present day.” When it comes to facing a possible future extinction of yet unknown degree, Saupe says the Earth has advantages it didn’t before. For one, we no longer live on one supercontinent, which means the climate regulates better and prevents the continental interiors from becoming so hot and dry. However, similar to McKinney, she is worried that resources are limited and humans are having a disproportionate effect on biodiversity. “In the past when you’ve had these major climatic changes, although it was devastating for biodiversity … species had the time, they had the resources for species to eventually rebound,” she says. “Today, we’re worried that those climatic changes will continue, but there is no space – there are more limited resources for species to cope with those changes.”