Bonapartenykus (meaning "José F. Bonaparte's claw") is a monospecific genus of alvarezsauroid dinosaur from Argentina that lived during the Late Cretaceous (Campanian-Maastrichtian) in what is now the upper Allen Formation of the Río Negro Province.

The type and only species, Bonapartenykus ultimus, is known from a nearly articulated but partial skeleton that was found in close association to two incomplete eggs and several clusters of eggshells belonging to the oogenus Arriagadoolithus.

A partial skeleton of a theropod with eggs was collected in a surface of approximately 30 m2 in fluvial sandstones of the upper Allen Formation in northwestern Patagonia, Argentina.

[3] In 2025, Meso and colleagues described various alvarezsaurid material first reported in the late 2000s from the same formation, specifically within the Salitral Ojo de Agua locality, as cf.

[3][7][4] Agnolin et al. (2012) diagnosed Bonapartenykus based on the presence of spinopostzygapophyseal laminae that end abruptly above the postzygapophyses of the mid-dorsal vertebrae; the underside portion of the coracoid being strongly deflected towards the middle and decorated with delicate but abundant grooves as in Xixianykus; fused scapulocoracoids as in Ceratonykus; scapula with a very wide notch on the posterior margin of the bone; and a fused ilium and pubis.

Unlike Haplocheirus and Patagonykus, the centrum has a cranial articular surface that is deeply concave with a sharp bony margin that surrounds it, which might be procoelous.

The mid-dorsal vertebrae has neural canals that are wide and prezygapophyses that shows a subcircular contour and a shallow concavity at its caudal margin.

The coracoidal foramen is wide and rounded in contour, and possesses several ridges near the caudal margin which may correspond to muscle attachment points.

This feature is similar in condition to that of Patagonykus but differs by the middle portion of the coracoid not being as strongly inflected towards and the surface of the side show only isolated and poorly developed grooves.

Alvarezsaurids like Bonapartenykus may have had a flat and wide breast based on a combination of characteristics like a continuous subhorizontal surface with formed by the medial deflection of the coracoids with the sternal plate.

Towards the sides of the base of the cnemial crest, a small bump is present and the distal end is strongly scraped by friction or erosion.

Their results are displayed in the cladogram below:[4] Shishugounykus Aorun Haplocheirus Bannykus Xiyunykus Tugulusaurus Alvarezsaurus Patagonykus MPCN-PV 738 (cf.

[12] The fauna of the Allen Formation consists of the titanosaur sauropods Bonatitan,[13] Menucocelsior,[14] Panamericansaurus,[15] Rocasaurus[16] and an indeterminate species of Aeolosaurus,[17] the hadrosaurid ornithopods Bonapartesaurus,[18] Kelumapusaura,[19] Lapampasaurus[20] and Willinakaqe,[21] the nodosaurid Patagopelta,[22] the abelisaurid theropods Niebla [23] and Quilmesaurus,[24] the large unenlagiid paravian Austroraptor,[25] the avialans Lamarqueavis[26] and Limenavis,[27] the azhdarchid pterosaur Aerotitan,[28] the rhynchocephalian Lamarquesaurus,[29] and the plesiosaur Kawanectes.