Genus: Bonapartenykus AGNOLIN, POWELL, NOVAS & KUNDRAT,
Etymology: The generic name honors the surname of the great Argentinean palaeontologist Jose F. Bonaparte, and Latin, onykus, 'claw'.
Species: ultimus AGNOLIN, POWELL, NOVAS & KUNDRAT,
Etymology: Latin, ultimus, 'latest'; in reference of the present record constitutes the geological youngest alvarezsaurid from South America.
Holotype: MPCA 1290
Locality: Salitral Ojo de Agua, Rio Negro Province, northwestern Patagonia, Argentina.
Horizon: Upper levels of the Allen Formation, Lower Malargue Group.
Age: Campanian-Maastrichtian Stage, Senonian Subepoch, Gulf Epoch, Late Cretaceous.
Material: A nearly articulated but badly preserved partial skeleton consisting of an incomplete mid-dorsal vertebra, a nearly comlpete left scapulocoracoid, incomplete right scapulocoracoid, incomplete left tibia and femur, nearly complete left pubis articulated with the incomplete pubic peduncle of ilium, and the anteior blade of the left ilium.
Note: Also associated with the skeletal elements are 2 partially preserved eggs.