Jaculinykus

Jaculinykus (meaning "Jaculus claw") is an extinct genus of alvarezsaurid theropod dinosaur from the Late Cretaceous Baruungoyot Formation of Mongolia. The genus contains a single species, J. yaruui, known from a nearly complete articulated skeleton including bones of the skull. Jaculinykus is notable for its unique hand, which has a hypertrophied first digit and greatly reduced second digit, which is intermediate between the tridactyl hand of Shuvuuia and monodactyl hand of Linhenykus.^[1]

Jaculinykus Temporal range: Late Cretaceous, 72–71 Ma PreꞒ Ꞓ O S D C P T J K Pg N ↓
Holotype specimen and skeletal reconstruction
Scientific classification
Domain:	Eukaryota
Kingdom:	Animalia
Phylum:	Chordata
Clade:	Dinosauria
Clade:	Saurischia
Clade:	Theropoda
Family:	†Alvarezsauridae
Subfamily:	†Parvicursorinae
Genus:	†Jaculinykus
Species:	†J. yaruui
Binomial name
†Jaculinykus yaruui Kubo et al., 2023

Discovery and naming

Occurrence of alvarezsaurids in Mongolia (Jaculinykus at center, zone 4)

The Jaculinykus holotype specimen, MPC-D 100/209, was discovered in sediments of the Baruungoyot Formation (Nemegt locality), of Ömnögovi Province, Mongolia. The specimen consists of a nearly complete skeleton with most of the skull.^[1]

In 2023, Kubo et al. described Jaculinykus yaruui as a new genus and species of parvicursorine alvarezsaurid based on these fossil remains. The generic name, "Jaculinykus", combines a reference to the Jaculus, a small dragon in Greek mythology with the Greek word "onykus," meaning "claw". The specific name "yaruui" is derived from "yaruu" ("яаруу"), the Mongolian word for "speedy" or "hasty".^[1]

Classification

Life restoration

Jaculinykus was added to a phylogenetic analysis and found to be in the clade Parvicursorinae, in a clade consisting of all alvarezsaurs from the Nemegt Basin. The cladogram from Kubo et al. (2023) is shown below:^[1]

Alvarezsauria	Aorun Haplocheirus Xiyunykus Tugulusaurus Bannykus Patagonykus Achillesaurus Alvarezsauridae Alvarezsaurus Albertonykus Qiupanykus Nemegtonykus Parvicursorinae Dzharaonyx Khulsanurus Linhenykus Parvicursor Ceratonykus Xixianykus Albinykus Ondogurvel Mononykus Jaculinykus Shuvuuia

Paleoecology

Restoration of the sleeping posture

Fossils of Ondogurvel, another parvicursorine alvarezsaurid, as well as fossils of Nemegtomaia, an oviraptorosaur, are also known from the Nemegt locality of the Mongolian Barun Goyot Formation.^[2] Other localities from the formation have yielded dinosaurs including additional alvarezsaurids (Ceratonykus, Khulsanurus, and Parvicursor),^[1] as well as dromaeosaurs (Hulsanpes,^[3] Kuru, and Shri^[4]), oviraptorosaurs (Conchoraptor and Heyuannia),^[5] a sauropod (Quaesitosaurus),^[6] ceratopsians (Bagaceratops and Breviceratops),^[7] a pachycephalosaur (Tylocephale),^[8] and ankylosaurs (Saichania,^[9] Tarchia,^[10] and Zaraapelta^[11]).