Tiny-armed alvarezsauroid dinosaurs might have been insect eaters, fossil scans suggest

June 1, 2026 feature Tiny-armed alvarezsauroid dinosaurs might have been insect eaters, fossil scans suggest Ingrid Fadelli Author Sadie Harley Scientific Editor Robert Egan Associate Editor Dinosaurs are estimated to have roamed Earth for over 165 million years, gradually evolving over time to survive in changing environments. Among the many fascinating groups of dinosaurs known to have lived on our planet are alvarezsauroids. These dinosaurs possessed extremely short but powerful forelimbs with only a few fingers attached to them. The reason why alvarezsauroids evolved to have such short and strong limbs has been widely debated. One leading hypothesis is that these limbs allowed them to dig into hard materials like wood, to access insect nests, which they then devoured. The consumption of insects, called myrmecophagy, is also common in many animals existing today, including anteaters, aardvarks, and pangolins. Researchers at University of Liverpool, University of Birmingham, University of Bristol, and other institutes recently tried to shed more light on what alvarezsauroids did with their small limbs. The findings of their study, published in Proceedings of the Royal Society B, appear to confirm the hypothesis that these dinosaurs used their forelimbs to dig. "Alvarezsaurs are a group of theropod dinosaurs with a collection of bizarre anatomical features," Sidney Leedham, first author of the paper, told Phys.org. "Most notably, their forelimbs, which are extremely short in proportion to the body, with the hand often reduced to only one or two functional fingers. Despite being so short, the arms of alvarezsaurs are chunky and robust, with large claws—this suggests that they were using their forelimbs for an important function. "Over the years, various researchers have suggested different scenarios, but the leading hypothesis is that they were using these unique forelimbs to dig into hard surfaces, possibly to extract insects to feed on like some modern mammals." Studying 3D digital models of alvarezsauroids So far, the biomechanical capabilities of alvarezsaur forelimbs have rarely been investigated directly. Leedham and her colleagues set out to fill this gap in the literature, gathering evidence that their forelimbs would have allowed them to dig. To do this, the researchers created three-dimensional (3D) digital models of the forelimb bones of two distinct alvarezsaur species, using CT scans of fossils as a reference. The species they focused on are Mononykus, a highly specialized member of the group, and Bannykus, an earlier-diverging species with longer forelimbs. "We used these models to perform computational range of motion analysis for the elbow and shoulder joints, to determine the maximum joint mobility of the two species," explained Leedham. "We also used measurements of the bones to calculate moment arms—a measure of how effectively muscles can produce rotation around a joint—for the forelimb muscles of both species, and compared these to a previously published dataset of living mammals." The 3D models created by Leedham and her colleagues, along with the measurements they collected, appeared to confirm the hypothesis they were testing. Specifically, they suggested that alvarezsauroids tended to heavily emphasize the same muscle groups that are more pronounced in modern specialized diggers, which would indicate that they used their forelimbs to perform similar movements. Deepening our understanding of dinosaur evolution The team's analyses suggest that it was not merely possible for alvarezsauroids to engage in digging behaviors, but that they had specifically evolved for these functions. This suggests that digging was an important part of their ecology and daily life. "This finding is consistent with the idea that they were insect eaters," said Leedham. "Bannykus, an earlier representative of the group, also appears to have been more versatile in its forelimb function and less similar to mammalian diggers than Mononykus, a later-diverging species. This indicates that alvarezsaurs evolved to become more specialized throughout their evolutionary history." Notably, the findings of this study also offer interesting insight into the possible evolution of dinosaurs and evolutionary processes in general. For instance, they could be evidence of a phenomenon known as convergent evolution. "If alvarezsauroids were specialized ant or termite eaters, they also represent a really exciting and intriguing possible example of convergent evolution," explained Leedham. "This is a phenomenon that consists in unrelated species evolving to look similar because they have adopted similar lifestyles—between dinosaurs and mammals." Other researchers could draw inspiration from this study and explore the possible function of alvarezsaur forelimbs further. Meanwhile, the team plan to continue studying distinct dinosaur groups, focusing on how their claws functioned and how they evolved to engage in specific behaviors. "We tend to think of claws as simple curved objects, but dinosaur claws were various shapes and sizes, and we think they were suited for diverse roles in different animals—digging, but also capturing prey, climbing, running and accommodating flight in some groups," added Emily Rayfield, Professor of Paleobiology at the University of Bristol, who was also involved in the research. "Using the same digital imaging methods and principles of physics and engineering, we are testing how efficiently different claw shapes rotated and transferred force from muscles and tendons to the claw tip, revealing more about how these extinct animals interacted with their environment." Written for you by our author Ingrid Fadelli, edited by Sadie Harley, and fact-checked and reviewed by Robert Egan—this article is the result of careful human work. We rely on readers like you to keep independent science journalism alive. If this reporting matters to you, please consider a donation (especially monthly). You'll get an ad-free account as a thank-you. Publication details Sidney Leedham et al, Range of motion and myology support a digging function for the forelimbs of alvarezsauroid dinosaurs, Proceedings of the Royal Society B: Biological Sciences (2026). DOI: 10.1098/rspb.2026.0565. Journal information: Proceedings of the Royal Society B Key concepts morphology (biological)vertebrate paleontologydinosaursAdaptation, BiologicalBiological Evolution© 2026 Science X Network