Haplocheirus

Haplocheirus is a genus of theropod dinosaur. Upon its description, it was considered the oldest alvarezsauroid, predating all other members by about 63 million years.[1] This has subsequently been questioned.[2] A 2019 study considered Haplocheirus a compsognathid instead of an alvarezsauroid,[3] while a 2022 study considered it to have more similarities with ornithomimosaurs.[2] Haplocheirus was described in 2010 from a fossil specimen found from the 160-million-year-old Shishugou Formation in the Junggar Basin of northwestern China.[4] The type species is H. sollers, meaning "simple-handed skillful one", referencing its hypothesized behavior of using its three-fingered hands for activities that other alvarezsauroids could not perform, such as catching prey.[1][5]

Haplocheirus
Temporal range: Late Jurassic,
Holotype specimen
Scientific classification Edit this classification
Domain: Eukaryota
Kingdom: Animalia
Phylum: Chordata
Clade: Dinosauria
Clade: Saurischia
Clade: Theropoda
Superfamily: †Alvarezsauroidea (?)
Genus: †Haplocheirus
Choiniere et al., 2010
Type species
†Haplocheirus sollers
Choiniere et al., 2010
Size of Haplocheirus compared to a human.

Description
Life restoration.

Haplocheirus had an enlarged thumb claw like alvarezsaurids, but also retained two other functional fingers, unlike alvarezsaurids, where only the thumb was significantly large and clawed. It had long legs and was probably a fast runner. It had large pupils for proportional for an animal its size.[6][7] According to one study, it and the alvarezsaurid Shuvuuia were likely nocturnal animals.[6][7]

As an alvarezsaur, it was among the largest members of the clade, with an estimated adult body mass of 41 kilograms (90 lb),[lower-alpha 1] though it was surpassed by Bonapartenykus.[8] The total length of the holotype, which was a still-growing juvenile, would have been roughly 190–230 centimetres (6.2–7.5 ft), depending on the length of the tail.[1]

See also

Footnotes
  1. The holotype individual of Haplocheirus sollers has been estimated to have had a mass of 20.45 kilograms (45.1 lb). However, it is a young juvenile, estimated to have died at four or five years of age. As such, it was probably roughly half the mass of an adult; based on other alvarezsaurs, maturity would be reached at 10–12 years of age.[8]

References
  1. Choiniere, J. N.; Xu, X.; Clark, J. M.; Forster, C. A.; Guo, Y.; Han, F. (2010). "A basal alvarezsauroid theropod from the Early Late Jurassic of Xinjiang, China". Science. 327 (5965): 571–574. Bibcode:2010Sci...327..571C. doi:10.1126/science.1182143. PMID 20110503. S2CID 36904501.
  2. Agnolín, Federico L.; Lu, Jun-Chang; Kundrát, Martin; Xu, Li (2022-03-04). "Alvarezsaurid osteology: new data on cranial anatomy". Historical Biology. 34 (3): 443–452. doi:10.1080/08912963.2021.1929203. ISSN 0891-2963. S2CID 236221732.
  3. Hartman, Scott; Mortimer, Mickey; Wahl, William R.; Lomax, Dean R.; Lippincott, Jessica; Lovelace, David M. (2019-07-10). "A new paravian dinosaur from the Late Jurassic of North America supports a late acquisition of avian flight". PeerJ. 7: e7247. doi:10.7717/peerj.7247. ISSN 2167-8359. PMC 6626525. PMID 31333906.
  4. Qin, Zichuan; Clark, James; Choinere, Jonah; Xu, Xing (2019). "A new alvarezsaurian theropod from the Upper Jurassic Shishugou Formation of western China". Scientific Reports. 9 (1): 11727. Bibcode:2019NatSR...911727Q. doi:10.1038/s41598-019-48148-7. PMC 6692367. PMID 31409823.
  5. "Guest post: Haplocheirus – the skilful one". Dave Hone's Archosaur Musings. 2010-01-29. Retrieved 2022-08-15.
  6. Choiniere, Jonah N.; Neenan, James M.; Schmitz, Lars; Ford, David P.; Chapelle, Kimberley E. J.; Balanoff, Amy M.; Sipla, Justin S.; Georgi, Justin A.; Walsh, Stig A.; Norell, Mark A.; Xu, Xing (2021-05-07). "Evolution of vision and hearing modalities in theropod dinosaurs". Science. 372 (6542): 610–613. Bibcode:2021Sci...372..610C. doi:10.1126/science.abe7941. PMID 33958472. S2CID 233872840.
  7. Choiniere, Jonah; Schmitz, Lars; Benson, Roger. "Nocturnal dinosaurs: Night vision and superb hearing in a small theropod suggest it was a moonlight predator". The Conversation. Retrieved 2021-12-29.
  8. Qin, Zichuan; Zhao, Qi; Choiniere, Jonah N.; Clark, James M.; Benton, Michael J.; Xu, Xing (2021-07-06). "Growth and miniaturization among alvarezsauroid dinosaurs". Current Biology. 31 (16): 3687–3693.e5. doi:10.1016/j.cub.2021.06.013. ISSN 0960-9822. PMID 34233160. S2CID 235752037.


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