Manipulonyx
Manipulonyx is an extinct genus of alvarezsaurid theropod dinosaurs known from the Late Cretaceous Nemegt Formation of Mongolia. The genus contains a single species, Manipulonyx reshetovi, known from a partial skeleton. This includes the most complete forelimb known from any member of the alvarezsaurid subfamily Parvicursorinae, including all of the proximal bones. Manipulonyx has been interpreted as an ovivore, with unique ossified spikes on the wrist that helped the animal to grasp eggs and an enlarged claw on the functionally-monodactyl hand being used to puncture the egg before consumption.
Discovery and naming
The Manipulonyx fossil material was discovered in 1979 by V. Yu. Reshetov in an outcrop of the Nemegt Formation in the Gobi Desert of Mongolia. The specimen is housed in the Paleontological Institute, [Russian Academy of Sciences|Paleontological Institute] of the Russian Academy of Sciences, where it is permanently accessioned as specimen PIN 3142/364. The specimen consists of several , the left, much of both forelimbs, a partial pelvic girdle, and fragments from both hindlimbs.In 2025, Alexander O. Averianov, Alexey V. Lopatin, and Andrey Atuchin described Manipulonyx reshetovi as a new genus and species of alvarezsaurid theropod based on these fossil remains, establishing PIN 3142/364 as the holotype specimen. The generic name, Manipulonyx, combines the Latin word manipulare, meaning or, with the Greek word wikt:ὄνυξ, meaning. The specific name, reshetovi, honors V. Y. Reshetov, the discoverer of the holotype.
Description
As a parvicursorine, Manipulonyx would have been a small theropod with distinctive short forelimbs, comprising a robust and functionally monodactyl hand with a greatly enlarged . The hindlimbs are slender and elongated, likely an indicator of cursorial behavior.The forelimb of Manipulonyx is especially notable, as it is the most completely known of any parvicursorine. The proximal and distal ends of the left humerus, as well as the distal end of the right humerus, are preserved. The and are co-ossified, with a suture still visible separating the two. The of the ulna is missing. Three are preserved, the,, and, articulating with the radius and ulna. The carpals are followed by the metacarpus, comprising three completely fused. This forms a large, complex element with which several other bones articulate. Manipulonyx has three manual digits, two of which are greatly reduced and the third of which is extremely large. A claw was present on each digit, with the enlarged second digit exhibiting an especially large, curved morphology. In addition to the digits, three small, conical spikes are preserved around the metacarpus, facing forward, backward, and inward. While Manipulonyx is the first alvarezsaurid found with these spikes, other species likely had them based on articular surfaces observed on their metacarpi. Like the claws, these spikes were likely covered in a keratinous sheath, increasing their size.
Paleobiology
The distinctive hand and forelimb of Manipulonyx raises questions about the behavior and ecology of this taxon and other alvarezsaurids, a point debated by previous researchers. Several authors have interpreted alvarezsaurids as myrmecophagous animals, using their hypertrophied claws in a 'hook-and-pull' fashion to access the nests of ants and termites, similar to modern anteaters. In their 2025 description of Manipulonx, Averianov and colleagues disputed this hypothesis, noting that, due to the extreme size discrepancy between the arms and legs of alvarezsaurids, they would have been unable to conveniently reach the ground. Their cursorial-adapted hindlimbs are also inconsistent with fossorial habits, and their shortened forelimbs would not have been efficient for digging.In their 2018 description of the alvarezsaurid Qiupanykus, Lü and colleagues proposed these animals were ovivorous based on the discovery of the specimen of this genus in association with oviraptorid eggshells. They suggested alvarezsaurids used their robust claws to break eggshells to be able to consume the egg's contents. Averianov et al. elaborated on this hypothesis based on the well-preserved forelimb of Manipulonyx. The region of the pectoral girdle where the humerus articulates is oriented posterolaterally, allowing both arms to more effectively grasp relatively large objects, such as an egg. A pronounced keeled sternum in parvicursorines indicates a stronger pectoralis muscle, improving their grasping abilities. The carpometacarpal spikes and vestigial fingers would have been used to support the egg, while the enlarged second claw would puncture the shell. Based on previous research suggesting nocturnal habits for the parvicursorine Shuvuuia, Averianov et al. concluded parvicursorines like Manipulonyx would have located dinosaur nests in the night, grabbed a single egg, and run away with it to a safe location before consumption. The optimal egg size to be grasped by an alvarezsaurid would be near the animal's body size.
The theory of nest-invading parvicursorines may explain the discovery of several members of this clade in association with dinosaur eggshells, including Manipulonyx, Qiupanykus, and the more distantly-related Bonapartenykus.