| Bonapartenykus | |
|---|---|
 | |
| Skeletal reconstruction based on specimen MPCN-PV 738 | |
Scientific classification | |
| Kingdom: | Animalia |
| Phylum: | Chordata |
| Class: | Reptilia |
| Clade: | Dinosauria |
| Clade: | Saurischia |
| Clade: | Theropoda |
| Superfamily: | †Alvarezsauroidea |
| Clade: | †Patagonykinae |
| Genus: | †Bonapartenykus Agnolin et al.2012 |
| Species: | †B. ultimus |
| Binomial name | |
| †Bonapartenykus ultimus Agnolin et al. 2012 | |
Bonapartenykus (meaning "José F. Bonaparte's claw") is an extinctgenus ofalvarezsauroid dinosaur that lived during theLate Cretaceous (Campanian–Maastrichtian) of what is now theAllen Formation of theRío Negro Province, Argentina. The genus contains asingle species,Bonapartenykus ultimus, known from a partially articulated, incomplete skeleton that was found in close association to two incompleteeggs and several clusters of eggshells belonging to theoogenusArriagadoolithus.Bonapartenykus was named in2012. It has an estimated length of 2.5–3.3 m (8.2–10.8 ft) and weight of 43–72 kg (95–159 lb), making it the largest member of the cladeAlvarezsauroidea. Additional skeletons referrable to this genus have subsequently been described.
A partialskeleton of atheropod with eggs was collected in a surface of approximately 30 m2 influvialsandstones of the upperAllen Formation in northwesternPatagonia,Argentina.[2] The locality has also produced specimens ofhadrosaurids,ankylosaurs, severaltitanosaursauropods, severalabelisaurids, indeterminatetetanurans, an incomplete large alvarezsaurid and a largeunenlagiid.[3] The skeleton was originally reported and described by Salgado et al. (2009) as an indeterminate alvarezsaurid.[2] The specimen was later redescribed and named in2012 by Federico L. Agnolin, Jaime E. Powell, Fernando E. Novas and Martin Kundrát. Theholotype specimen, MPCA, 1290, consists of a mid-dorsalvertebra, bothscapulocoracoids, lefttibia andfemur, leftpubis articulated with the pubic peduncle of theilium, 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 toBonapartenykus: MGPIFD-GR 166 and MGPIFD-GR 184, a blade of the left scapula, a leftcoracoid, a distal right pubis, four cervical vertebrae and a single caudal vertebra which all belong to the same individual.[3]
The eggs ofBonapartenykus were considered unique enough for them to be given a newparataxonomic name,Arriagadoolithus, which was classified in a newoofamily, theArriagadoolithidae, so named for the owner of the site where the discovery was made.[3]
The generic name,Bonapartenykus, is derived from the ArgentineanpaleontologistJosé F. Bonaparte and theLatin word "onykus" (claw). The specific name,ultimus, is derived from the Latin word "ultimus" (latest), as it is one of the geologically youngest alvarezsaurids fromSouth America.[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, ascf.Bonapartenykus ultimus.[1][4][5]
Bonapartenykus was a large alvarezsaur, measuring 2.5–3.3 m (8.2–10.8 ft) long and weighing 43–72 kg (95–159 lb).[3][6][1]
Agnolin et al. (2012) diagnosedBonapartenykus based on the presence of spinopostzygapophyseal laminae that end abruptly above thepostzygapophyses 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 inXixianykus; fused scapulocoracoids as inCeratonykus; scapula with a very wide notch on the posterior margin of the bone; and a fused ilium and pubis.[3]
The mid-dorsal vertebrae has diapophyses and parapophyses that are worn, with the former lacking its distal ends. As in other alvarezsaurids, the centrum of the mid-dordsal vertebrae lack pleurocoels. UnlikeHaplocheirus andPatagonykus, the centrum has a cranial articular surface that is deeply concave with a sharp bony margin that surrounds it, which might be procoelous. The neural spine is proportionally taller than inMononykini, but also resembles the condition seen in basal alvarezsauroids such asHaplocheirus. As inMononykus andPatagonykus, both the prespinal and postspinal fossae are very deep. A unique feature ofBonapartenykus is the spinopostzygapophyseallaminae ending abruptly above the rear margin of the postzygapophyses. 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. As inPatagonykus, the parapophyses connect to the margins of the cranial articular surface through a small ridge and the diapophyses connect to the parapophyses by a deep ridge. The centrodiapophyseal lamina was craniocaudally wider than in other alvarezsaurids, based on the preserved portions. The postzygapophyses areellipsoidal in contour in dorsal view and show a notched caudal margin. The postzygapophyses are transversely wide and craniocaudally shortened, but lacks a lateroventral projection.[3]
As inAlvarezsaurus, the scapular blade is medially deflected, unlike other alvarezsaurids that have a straightscapular blade. However, as in other alvarezsaurids, both the cranial and caudal margins are almost parallel. Along the caudal margin of the scapular blade is a well-developed notch. As inManiraptora,Oviraptorosauria and other Alvarezsauridae, theacromion is subtriangular in shape. Theglenoid fossa is oriented towards the posterior and sides, with the scapular portion being lateromedially expanded and wider than the coracoidal portion, as well as perpendicular to the main axis of the coracoid. Similar toParaves, the ventral half of the coracoid is strongly medially flexed. The coracoid lacks abicipital tubercle and is transversely thick at the cranial margin. The coracoidal foramen is wide and rounded in contour, and possesses several ridges near the caudal margin which may correspond tomuscle attachment points. Along the side margins of the coracoid are a smooth surface towards the sides and upper side and a directed margin towards the middle and underside. This feature is similar in condition to that ofPatagonykus 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. The faintly defined ridge ofCeratonykus is very poorly and is restricted to the posterior end of the coracoid which is unlike that ofBonapartenykus. Agnolin et al. (2012) noted that the ventral half of the coracoid is deflected towards the middle, with an extremely thin medial rear that is slightly wrapping upwards which probably correlates with some kind ofskin cornification, but does not correlate with a cornified sheath due to the absence of oblique neurovascular foramina. The coracoid is extremely elongate and ends at an acute end which restricted articulation with the sternum. Alvarezsaurids likeBonapartenykus 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.[3]
UnlikePatagonykus, the pubic shaft ofBonapartenykus is more compressed towards the sides and narrower from front to back. As in derived alvarezsaurids, the pubic shaft lacks the caudalsulcus 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. Thefemoral head was separated from thegreater trochanter by a cleft as indicated by the base of the cranial trochanter. The femoral head was similar in general size and proportions toPatagonykus. In lateral view, a large, sculptured bulge is present on the femur, which may correspond to muscle attachment points. Thetibia is very short and robust, while the tibial shaft is bowed towards the sides. Towards the sides of the base of thecnemial crest, a small bump is present and the distal end is strongly scraped by friction or erosion.[3]
In theirphylogenetic analyses, Agnolin et al. (2012) originally placedBonapartenykus withinAlvarezsauridae, within the clade Patagonykinae assister taxon toPatagonykus.[3] Other analyses by Averianov & Lopatin in 2022 similarly recovered it as the sister taxon toPatagonykus, albeit outside of Alvarezsauridae.[7][8] However, Xu et al. (2018) and subsequent analyses using their dataset recovered it as a non-alvarezsauridalvarezsauroid, more basal thanPatagonykus andAchillesaurus.[9][10]
In their 2025 description of bones they referred toBonapartenykus, 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 thecladogram below:[1]
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Bonapartenykus is known from fluvial sandstones of the upper Allen Formation which have been dated to theCampanian toMaastrichtian stages of theLate Cretaceous period.[3] The Allen Formation represents a range of environments such as ephemerallacustrine,aeolian andfluvial systems to coastal marine environments that developed intoestuaries andtidal flats.[11] 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.[11]
The fauna of the Allen Formation consists of thetitanosaursauropodsBonatitan,[12]Menucocelsior,[13]Panamericansaurus,[14]Rocasaurus[15] and an indeterminate species ofAeolosaurus,[16] thehadrosauridornithopodsBonapartesaurus,[17]Kelumapusaura,[18]Lapampasaurus[19] andWillinakaqe,[20] thenodosauridPatagopelta,[21] theabelisauridtheropodsNiebla[22] andQuilmesaurus,[23] the largeunenlagiidparavianAustroraptor,[24] theavialansLamarqueavis[25] andLimenavis,[26] theazhdarchidpterosaurAerotitan,[27] therhynchocephalianLamarquesaurus,[28] and theplesiosaurKawanectes.[29]
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