11,000 measurements, a 1940s radar trick, and a dinosaur that would not stay on land
What happened
Palaeontologists have argued for years about Spinosaurus. Was it a swimmer that chased fish underwater like a seal? Or a wader that stood in the shallows and stabbed at them like a heron? A team based at Yale University has come down firmly on the swimming side, using an unusual method. Rather than studying Spinosaurus on its own, they built a tool that reads lifestyle from limb proportions. They examined hundreds of fossil and modern specimens, including holdings at the Yale Peabody Museum and collections elsewhere. They gathered over 11,000 measurements, plus photographs and CT scans. Then they trained machine learning models on living animals, where the answer is already known. If you can tell from an otter’s bones that it swims, and from a deer’s bones that it does not, you can apply the same rule to something extinct. They also borrowed a statistical method from the 1940s, originally built to judge whether a blip on a radar screen was an enemy aircraft. The question there and here is the same shape: given a faint signal, how confident can you be? Forelimb proportions turned out to be especially telling. The models predicted flippers, and highly or fully aquatic habits, with more than 90% accuracy. Applied to Spinosaurus, which lived in northern Africa roughly 113 to 94 million years ago, the result was clear. Caleb Gordon, the lead author, said the findings “indicate that it spent the vast majority of its time submerged”. The study was published in the journal Current Biology, and Yale set out the findings in a release reported on 25 October 2026.
Why this matters
The Spinosaurus argument matters more than one dinosaur’s habits, because it is really an argument about method. Fossils rarely answer behaviour questions directly. Bones do not record where an animal spent its afternoons. So palaeontologists reason from shape to life, and reasonable people reading the same bones have reached opposite conclusions. A tool trained on living animals, tested for accuracy, and applied consistently is a step forward. It does not depend on one expert’s intuition, and it can be checked by others. The study also turned the method on animals nobody was arguing about, and got a surprise. Mesosaurs lived 290 to 274 million years ago in what is now South Africa and eastern South America, and have often been described as fully aquatic. The models disagreed. Their limbs were not built for a fully aquatic life. Gordon said they “didn’t completely leave the land behind”. That led to a broader claim: no Palaeozoic marine reptile appears to have become fully aquatic. Even the most water-adapted stayed amphibious. The full commitment to the sea came later. So one animal moved into the water, and a group of animals moved back out. That is a useful reminder that the textbook version of evolutionary history is a simplification, and keeps getting revised.
What the evidence actually says
The study is careful about its own reach, and so should any summary of it be. It says Spinosaurus spent most of its time submerged. It does not settle how it hunted. Being underwater and chasing prey at speed are different claims, and the authors only make the first. The accuracy figure — more than 90% — applies to the models predicting flippers and highly or fully aquatic habits. That is good, not perfect. Roughly one call in ten could be wrong, and we cannot know which. The models were trained on living animals and then applied to extinct ones. That is the standard approach, and it carries a built-in assumption: that the relationship between bone shape and lifestyle held 100 million years ago as it does today. Reasonable, but an assumption. The team did account for evolutionary relationships, which matters. Closely related animals share bone shapes because they are related, not only because they live similarly, and failing to allow for that can manufacture false patterns. The mesosaur result cuts against a long-standing reading of the evidence. Some researchers have treated live birth in mesosaurs as a sign of fully aquatic life. This analysis challenges that interpretation rather than disproving it, and the debate will continue. The senior author is Bhart-Anjan Bhullar of Yale’s Faculty of Arts and Sciences and the Peabody Museum. The paper is “Limb proportions predict aquatic habits and soft-tissue flippers in extinct amniotes”, in Current Biology.
Practical advice
If you are a student, a teacher, or a parent fielding dinosaur questions, there is something genuinely useful in this story beyond the animal itself. Notice what the researchers did when faced with a question that could not be answered directly. They did not argue harder. They built a measuring tool, tested it on cases where the answer was known, reported how often it got those right, and only then applied it to the unknown case. That sequence is worth more than any individual fact about Spinosaurus. Notice also where the method came from. A technique for reading radar blips in the 1940s turned out to fit a problem in palaeontology eighty years later. Ideas move between fields far more than school subject boundaries suggest, which is a good argument for being curious outside your own subject. If a child asks whether Spinosaurus swam, the honest and more interesting answer is: most researchers now think it spent most of its time underwater, there is a real argument about how it caught its food, and here is how scientists try to settle arguments like that. Museum collections did the heavy lifting here — drawers of bones catalogued decades ago by people who had no idea what they would one day be used for. Most UK museums are free. They are also where this kind of work actually happens.
What to know
Yale-based researchers gathered more than 11,000 measurements from hundreds of fossil and modern specimens, trained machine learning models on living animals, and used the result to read lifestyle from limb proportions. Forelimb shape predicted flippers and highly or fully aquatic habits with over 90% accuracy. Applied to Spinosaurus, which lived around 113 to 94 million years ago, the models indicate it spent the vast majority of its time submerged. The study does not settle how it hunted. The same method found that mesosaurs, often described as fully aquatic, were not built for it, and moved regularly between water and land. The authors report that no Palaeozoic marine reptile appears to have become fully aquatic. The approach carries assumptions — chiefly that bone shape related to lifestyle in the past as it does now — and better than nine in ten accuracy still means some calls are wrong. Sources: Yale University, “New evidence suggests spinosaurus spent most of its life underwater”, ScienceDaily, 25 October 2026, https://www.sciencedaily.com/releases/2026/10/261024221956.htm; Gordon, C. M., et al., “Limb proportions predict aquatic habits and soft-tissue flippers in extinct amniotes”, Current Biology, https://doi.org/10.1016/j.cub.2025.10.068 This article is for general information and does not replace advice from a doctor, pharmacist or other qualified healthcare professional.
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