Product Code Database
Bonapartenykus (meaning "José F. Bonaparte's claw") is an extinct genus of alvarezsauroid dinosaur that lived during the Late Cretaceous (Campanian–Maastrichtian) of what is now the Allen Formation of the Río Negro Province, Argentina. The genus contains a monotypic taxon, Bonapartenykus ultimus, known from a partially articulated, incomplete skeleton that was found in close association to two incomplete egg and several clusters of eggshells belonging to the egg fossils Arriagadoolithus. Bonapartenykus was named in 2012. It has an estimated length of and weight of , making it the largest member of the clade Alvarezsauroidea. Additional skeletons referrable to this genus have subsequently been described.
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.
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 geologically youngest alvarezsaurids from South America.
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. Bonapartenykus ultimus.
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 Patagonykus, the pubic shaft of Bonapartenykus is more compressed towards the sides and narrower from front to back. As in derived alvarezsaurids, the pubic shaft lacks the caudal sulcus for the ischial articulation. The distal end of the pubic shaft possesses a small ridge on its cranial margin, which is absent in more derived alvarezsaurids, but shows a distal pubic boot on the pubis. The pubic boot appears to be rounded in side view on the rear margin. A small portion of the right ilium is preserved. The pubic pedicle is compressed towards the middle and sides. The pubic pedicle is also strongly fused with the pubis, which is a characteristic unique among alvarezsaurids, along with a reduced cuppedicus fossa. The cuppedicus fossa is shallow and elongate with a low, wide, and smooth ridge being present above it. The femoral head was separated from the greater trochanter by a cleft as indicated by the base of the cranial trochanter. The femoral head was similar in general size and proportions to Patagonykus. In lateral view, a large, sculptured bulge is present on the femur, which may correspond to muscle attachment points. The tibia is very short and robust, while the tibial shaft is bowed towards the sides. 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.
In their 2025 description of bones they referred to Bonapartenykus, Meso et al. recovered it as a patagonykine within the Alvarezsauridae, similar to the initial description by Agnolin et al. (2012). Their results are displayed in the cladogram below:
Paleoenvironment
Bonapartenykus is known from fluvial sandstones of the upper Allen Formation which have been dated to the Campanian to Maastrichtian stages of the Late Cretaceous period. The Allen Formation represents a range of environments such as ephemeral lacustrine, aeolian and fluvial systems to coastal marine environments that developed into estuary and . In 2015, Armas and Sánchez described the relationship of the coastal environment with wind systems of the Allen Formation and concluded the formation represents a hybrid coastal system of tidal flats with a large storm influence in some areas linked to aeolian systems.
The fauna of the Allen Formation consists of the titanosauria sauropods Bonatitan,Martinelli, A. and Forasiepi, A.M. (2004). "Late Cretaceous vertebrates from Bajo de Santa Rosa (Allen Formation), Rio Negro province, Argentina, with the description of a new sauropod dinosaur (Titanosauridae)". Revista del Museo Argentino de Ciencias Naturales 6(2): 257–305. Menucocelsior, Panamericansaurus, RocasaurusSalgado, L. and C. Azpilicueta. (2000). Un nuevo saltasaurino (Sauropoda, Titanosauridae) de la provincia de Río Negro (Formacíon Allen, Cretácico Superior), Patagonia, Argentina. Ameghiniana 37 (3):259-264. and an indeterminate species of Aeolosaurus, the hadrosauridae ornithopods Bonapartesaurus, Kelumapusaura, Lapampasaurus and Willinakaqe, the nodosaurid Patagopelta, the abelisauridae theropods Niebla antiqua and Quilmesaurus, the large unenlagiidae paraves Austroraptor, the avialae Lamarqueavis and Limenavis,Clarke and Chiappe, 2001. "A new carinate bird from the Late Cretaceous of Patagonia (Argentina)". American Museum Novitates. 3323, 1-23. the azhdarchidae pterosaur Aerotitan, the rhynchocephalia Lamarquesaurus, and the plesiosauria Kawanectes.
|
|
