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In paleontology, bones may steal the show. But to comparative biologist Armita Manafzadeh, joints are where the action is. As she sees it, almost every animal with a backbone that has ever walked, flown, swum or slithered across the planet has done so because of joints. It’s an understudied part of the evolutionary puzzle.

Manafzadeh, soon to set up her own lab at the Georgia Institute of Technology, started her joint research in pterodactyls, which are often depicted as flying like bats, with their legs extended behind them. But by studying hip ligaments in birds—distant living relatives of pterodactyls—Manafzadeh showed that a batlike leg pose was probably impossible in the extinct reptiles. She uses CT scans of animals’ bones paired with high-speed video of the animal moving—say, an alligator walking on a treadmill—to build “4D x-ray vision” animations. The resulting scans show how the animals’ skeletons move inside their bodies.

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This technology, called x-ray reconstruction of moving morphology (XROMM), has allowed Manafzadeh and her colleagues to “reanimate” extinct animals to figure out how they might have moved when they were alive. Her team has found, for example, that compared with the bones of nonavian dinosaurs, the small size of the fibula in birds has been a critical adaptation, allowing the animals to rotate their knee joints by more than 100 degrees. Their closest living relative, the alligator, can’t do this. Without the reduction in fibula size, “we probably wouldn’t have the diversity of modern birds that we have today,” she says.

Manafzadeh hopes to continue investigating how and why joints and jointed limbs arose across the animal kingdom, including in invertebrates such as shrimp, crabs, ants and wasps. But starting a lab is difficult under the current federal-funding circumstances. “I think it’s deeply important that we do support that kind of work,” she says, “but I think the outlook isn’t entirely clear at this moment.”

This article is part of “The Young American Scientists,” an editorially independent project that was produced with financial support from Regeneron.