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. Bonapartenykus was named in 2012 by Federico L. Agnolin, Jaime E. Powell, Fernando E. Novas and Martin Kundrát.[1] Bonapartenykus has an estimated length of 2.5 m (8.2 ft) and weight of 72 kg (159 lb), making it the largest member of the clade Alvarezsauroidea.
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.[2] The locality has also produced specimens of hadrosaurids, ankylosaurs, several titanosaur sauropods, several abelisaurids, indeterminate tetanurans, an incomplete large alvarezsaurid and a large unenlagiid.[1] The skeleton was originally reported and described by Salgado et al. (2009) as an indeterminate alvarezsaurid.[2] The specimen was later redescribed and named in 2012 by Federico L. Agnolin, Jaime E. Powell, Fernando E. Novas and Martin Kundrát. The holotype specimen, MPCA, 1290, consists of a mid-dorsal vertebra, both scapulocoracoids, left tibia and femur, left pubis articulated with the pubic peduncle of the ilium, the anterior blade of the left ilium, and two partially preserved eggs that were separated from the holotype by less than 20 cm (7.9 inches). Two specimens were referred to Bonapartenykus: MGPIFD-GR 166 and MGPIFD-GR 184, a blade of the left scapula, a left coracoid, a distal right pubis, four cervical vertebrae and a single caudal vertebra which all belong to the same individual.[1]
The eggs of Bonapartenykus were considered unique enough for them to be given a new parataxonomic name, Arriagadoolithus, which was classified in a new oofamily, the Arriagadoolithidae, so named for the owner of the site where the discovery was made.[1]
The generic name, Bonapartenykus, is derived from the Argentinean paleontologist José F. Bonaparte and the Latin word "onykus" (claw). The specific name, ultimus, is derived from the Latin word "ultimus" (latest), as it is one of the most geologically youngest alvarezsaurid from South America.[1]
Bonapartenykus was a large alvarezsaur, measuring 2.5 m (8.2 ft) long and weighing 72 kg (159 lb).[1][3]
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.[1]