Sixty-seven million years ago in the Gobi Desert of Mongolia, a small, fast-running dinosaur grabbed a dinosaur egg, locked its short forelimb onto the slippery shell with special wrist spikes, and drove a giant claw straight through to steal a quick meal.
That same forelimb, now preserved as a nearly complete fossil, gives scientists the clearest look yet at how one of the strangest groups of dinosaurs actually lived. The discovery, described in a new study published in the Proceedings of the Zoological Institute RAS, overturns the old idea that these animals dug for insects and instead points to a life spent stealing eggs.
The researchers hypothesized that “parvicursorines were egg-eating animals, and they used these spikes (covered by a keratinous sheath), as well as rudimentary side fingers, to fix the forelimb on the round and elusive egg surface. After such fixation, the eggshell was punctured by the hypertrophied manual claw.”
Paleontologists found the fragmentary skeleton in 1979 at the Khermeen Tsav site in the Nemegt Formation. For decades, the bones sat in a museum drawer. Only recently did a team led by Alexander Averianov from the Zoological Institute of the Russian Academy of Sciences CT-scan the specimen and build three-dimensional models. The scans revealed something never seen before in this dinosaur group: a full set of wrist bones plus three sharp spikes attached to the hand — two on the sides and one on the palm.
The dinosaur, named Manipulonyx reshetovi in honor of its discoverer, had long, slender hind legs built for sprinting and short, powerful front limbs. One finger carried an enormous claw; two tiny side fingers remained; and the wrist spikes were perfectly placed to grip a smooth egg while the big claw did the piercing.
For years, scientists thought these dinosaurs lived like modern anteaters, digging for insects. The new fossil shows that the idea does not fit. “This interpretation is supported by a number of morphofunctional traits of the parvicursorine forelimb discussed in the paper, including the hypertrophied deltopectoral crest of the humerus, keeled sternum, enlarged ectepicondyle of humerus, hypertrophied olecranon of ulna, and lack of the flexor tubercle on the main manual ungual phalanx,” the study notes.
The paper conclude that the “above-discussed and other morphofunctional traits of Parvicursorinae allow us to assume that these animals were nocturnal hunters of dinosaur eggs and that they specialized in feeding on eggs.”
Citations
A. O. Averianov et al. Forelimb structure and function in a new Late Cretaceous parvicursorine theropod dinosaur from Mongolia. Proceedings of the Zoological Institute RAS. Published online December 23, 2025. DOI: 10.31610/trudyzin/2025.329.4.382
