At the Field Museum in Chicago, behind a series of access-controlled doors are approximately 1,500 dinosaur fossils. Paleobiologist Jasmina Wiemann walks straight past the bleached bones – some as big as she is – and doesn’t look at the fully intact spinal cord, stained red by iron oxides that fill the spaces where organic material once was. She only has eyes for the deep chocolate brown fossils: these are the fossils that contain preserved organic material – bones that offer unprecedented insights into creatures that went extinct millions of years ago.
Wiemann is part of the fast-growing field of paleobiology, where researchers look to the deep past to predict future vulnerability to extinction. At a time when humans are about to witness a sixth mass extinction, studying fossil data is particularly useful for understanding how the natural world responded to problems before we arrived: how life on Earth evolved over of time responded to environmental changes, how species adapted to planet-scale temperature changes, or what to expect as geochemical cycles in the ocean change.
“This is not something we can simulate or meaningfully observe in the laboratory today,” says Wiemann. “We have to rely on the longest-running experiment.”
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To observe that experiment on a planetary scale, scientists have developed new methods to gather 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 an area on her computer screen that is fifty times its original size, and moves over the surface of the fossil until she finds a dark spot with an apparently velvety surface: this is the fossilized organic matter.
Wiemann turns off the room lights, a small point of light falls on the fossil and a curved line appears on the computer screen. Each compound responds differently to the laser, and the bumps in this line on her chart indicate that she was successful in finding organics. “This is beautiful,” she says. She will have to review the data later, but this should reveal whether the specimen under her microscope was warm or cold blooded.
If you think about what the world will look like in a thousand years, I think deep time can help us answer that question
Michael McKinney
Using this method, Wiemann studied when warm-bloodedness emerged around the Permian-Triassic mass extinction (the largest in history) and the Cretaceous-Paleogene (when the dinosaurs went extinct). Warm-bloodedness was already a factor that made species less likely to become extinct, because they can regulate their internal temperatures in changing climates. But Wiemann found a new result: many animals independently developed warm-bloodedness after each of these extinctions. This could impact how animals adapt and find resilience as the planet warms.
“If we want to make meaningful predictions in any way, even in the short term, we need to demonstrate that we understand these processes,” she says.
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One of the first people to write about combining ecological and paleontological approaches to predict vulnerability to extinction was Michael McKinney, now director of environmental studies at the University of Tennessee. After graduating with a degree in paleontology, he started working, but he said he kept feeling the need to be more relevant. “I love the dinosaurs, the big picture,” he says. “But I kept thinking that it gave us great context, but it didn’t teach me much that I could immediately apply to the immediate problems.”
McKinney then founded his current department, which merges geology and ecology. Now he sees paleobiology as useful for predicting what will happen. But understanding what to do about it is more difficult.
“If you think about what the world will look like in a thousand years, I think deep time can help us answer that question,” he says. “But if I worry about the Amazon rainforest disappearing in the next 20 years, I’m skeptical that time can tell.”
Humans, he says, have found new ways to drive species to extinction, from the passenger pigeon to the dodo. “We apply rules that do not really apply to the past. The things we do are so fast and so unpredictable.”
But deep time can provide insight into how species respond to very large, systemic changes – like the temperature shifts we’re seeing now. Erin Saupe, professor of paleobiology at the University of Oxford, uses large data sets to look at extinction patterns in the fossil record to see which traits make species most vulnerable.
In a recent paper published in Science, she and her co-authors wondered whether intrinsic traits, including body size and geographic extent, were more or less important in predicting extinction than external factors such as climate change. “No one has looked at this question before,” says Saupe. Previous research has shown that larger animals are generally less likely to become extinct in marine environments, but are more susceptible to extinction on land, and that larger ‘range sizes’ – the distance over which a species is dispersed – help species avoid extinction.
The team used a digital database to look at 290,000 fossils of marine invertebrates from the past 485 million years and used models to reconstruct the climate over that period. They found that geographic range size was the most important predictor of extinction, perhaps because of its interrelationship with other factors associated with lower extinction risk. A large range size suggests that the animal is also good at covering greater distances, and if a species is widely distributed, a regional climate change in one area would be unlikely to affect all populations. The team found that all the intrinsic features they looked at, as well as climate change, were important in predicting extinctions.
Related: ‘Small but mighty’: how invertebrates play a central role in shaping our world
“Even if a species has traits that make it generally resistant to climate change and extinction, they will still become extinct if the magnitude of climate change is large enough,” says Saupe. “I think it’s a very important message for this time.”
When it comes to facing a possible future extinction of yet unknown magnitude, Saupe says Earth has advantages it didn’t have before. First, we no longer live on one supercontinent, which means it regulates the climate better and prevents the continental interior from becoming so hot and dry. However, like McKinney, she is concerned that resources are limited and that humans have a disproportionate impact on biodiversity.
“If you’ve had major climate changes in the past, even though they were devastating to biodiversity… species had the time and resources to eventually allow species to recover,” she says. “Today we fear that those climate changes will continue, but there is no room for that – there are more limited resources for species to deal with those changes.”
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