Reorganization of the theropod wrist preceded the origin of avian flight
Abstract
The carpus (wrist) of birds has a complex evolutionary history, long known to involve carpal reduction and recently shown to include topological replacement of one carpal (the ulnare) by another (the pisiform)1. The pisiform plays a crucial role in stabilization of the distal wingtip during flight 2, and facilitates kinematic integration that 'automates' wing motion 3. The apparent absence of a pisiform in all but the earliest theropod dinosaurs led to the proposal that it was lost early in theropod evolution and regained only in birds as a key step in the origin of flight 1. Here, we describe the forelimb skeletons of two newly prepared theropod dinosaur specimens from the Gobi Desert of Mongolia, each of which preserves a pisiform, establishing its presence in Oviraptorosauria and Troodontidae in addition to birds. Reinterpretation of published material in light of these specimens shows a pisiform in a wide range of theropod species, including Microraptor 4, Ambopteryx 5 and Anchiornis 6. Our results indicate that the pisiform replaced the ulnare by origin of the clade Pennaraptora, phylogenetically coincident with the hypothesized origin(s) of flight in birds and their closest relatives 7,8. Taken together, our results indicate that replacement of the ulnare by the pisiform was a terminal step in assembly of the dinosaurian flight apparatus that occurred close to the origins of flight in theropod dinosaurs, rather than a novelty restricted to birds.
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Adaptations of the wrist necessary for wing folding evolved outside of Aves to protect elongate forelimb feathers.
“Adaptations of the wrist necessary for wing folding evolved outside of Aves in order to protect the elongate forelimb feathers [41, 42].”
From The ecology of Archaeopteryx (2026) · cites this paper as [42]
Cites
Archaeopteryx and the origin of birds
OSTROM, J. H. (1976) · Biological Journal of the Linnean Society · doi:10.1111/j.1095-8312.1976.tb00244.x · Cited by 361 · see citing works
Brusatte, S. L., Lloyd, G. T., Wang, S. C., & Norell, M. A. (2014) · Current Biology · doi:10.1016/j.cub.2014.08.034 · Cited by 313 · cited 2× · see citing works
“…is placed as the earliest-diverging group of oviraptorosaurs in accordance with the phylogenetic results of several recent studies 48,52,54 , but we note that this enigmatic clade has been recovered as the basal-most lineage in Paraves 5,46,55 , or as an early-diverging avialan…”
Self-citationA Jurassic avialan dinosaur from China resolves the early phylogenetic history of birds
Godefroit, P., Cau, A., Dong-Yu, H., Escuillié, F., Wenhao, W., & Dyke, G. (2013) · Nature · doi:10.1038/nature12168 · Cited by 216 · cited 1× · see citing works
“Intriguingly, Anchiornis has previously been interpreted as having equivocal flight capability on the basis of biomechanical modelling 7 , whereas Eosinopteryx has been consistently interpreted as a terrestrial animal 50 .”
A bizarre Jurassic maniraptoran theropod with preserved evidence of membranous wings
Xu, X., Zheng, X., Sullivan, C., Wang, X., Xing, L., Wang, Y., Zhang, X., O’Connor, J. K., Zhang, F., & Pan, Y. (2015) · Nature · doi:10.1038/nature14423 · Cited by 187 · see citing works
Self-citationPotential for Powered Flight Neared by Most Close Avialan Relatives, but Few Crossed Its Thresholds
Pei, R., Pittman, M., Goloboff, P. A., Dececchi, T. A., Habib, M. B., Kaye, T. G., Larsson, H. C. E., Norell, M. A., Brusatte, S. L., & Xu, X. (2020) · Current Biology · doi:10.1016/j.cub.2020.06.105 · Cited by 137 · cited 4× · see citing works
“…eleven primary feathers (exclusively seen in flying birds today) 8 , and biomechanical analyses suggest that several were capable of powered flight 7 , but functionally asymmetrical primary feathers—which are strongly correlated with flight in extant birds—are at present not known outside Paraves…”
InfluentialSelf-citationReduced plumage and flight ability of a new Jurassic paravian theropod from China
Godefroit, P., Demuynck, H., Dyke, G., Hu, D., Escuillié, F., & Claeys, P. (2013) · Nature Communications · doi:10.1038/ncomms2389 · Cited by 124 · see citing works
Functional osteology of the avian wrist and the evolution of flapping flight
Vazquez, R. J. (1992) · Journal of Morphology · doi:10.1002/jmor.1052110303 · Cited by 100 · cited 1× · see citing works
“One key role of the pisiform in modern birds is stabilization of the carpometacarpus, an action attributed to the presence of a large muscular process 2 that is absent in the specimens described herein and all non-avialan theropods.”
Hartman, S., Mortimer, M., Wahl, W. R., Lomax, D. R., Lippincott, J., & Lovelace, D. M. (2019) · PeerJ · doi:10.7717/peerj.7247 · Cited by 86 · cited 1× · see citing works
“…is placed as the earliest-diverging group of oviraptorosaurs in accordance with the phylogenetic results of several recent studies 48,52,54 , but we note that this enigmatic clade has been recovered as the basal-most lineage in Paraves 5,46,55 , or as an early-diverging avialan lineage 54,56 .”
Functional constraints on the number and shape of flight feathers
Kiat, Y., & O’Connor, J. K. (2024) · Proceedings of the National Academy of Sciences · doi:10.1073/pnas.2306639121 · Cited by 30 · see citing works
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Resolving the “Ontogeny Problem” in Vertebrate Paleontology
Napoli, J. G. (2024) · bioRxiv · doi:10.1101/2024.10.25.620216 · Cited by 8
“…dermal roof bones (Fabbri et al. 2017); the identity of the carpal ossifications in living birds and their theropod ancestors (Botelho et al. 2014; Napoli et al. 2025); and the evolutionary transformations that ultimately created unique avian pelvic and hindlimb anatomy (Egawa et al. 2018, 2022;…”
Self-citationYu, D., Zhang, H., Zhou, C.-F., & Pei, R. (2026) · Swiss Journal of Palaeontology · doi:10.3897/sjp.145.196379 · Cited by 1 · see citing works
Morphology of the forelimb of Confuciusornis and its implications for early flight evolution
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O’Connor, J. K., & Clark, A. D. (2026) · Discover Ecology · doi:10.1007/s44396-026-00026-z
Self-citationPostcranial osteology of the giant oviraptorosaur Gigantoraptor erlianensis
Hao, M.-Z., Tan, Q.-W., & Xu, X. (2026) · Journal of Vertebrate Paleontology · doi:10.1080/02724634.2026.2716748
Olson, M. E. (2026) · doi:10.1093/9780197831533.001.0001
Display functions of dinosaur proto-wings before powered flight
Park, J., Son, M., Kim, W., Lee, Y.-N., Lee, S.-I., & Jablonski, P. G. (2026) · bioRxiv · doi:10.64898/2026.04.05.714230
- Authors
- Napoli, J. G., Fabbri, M., Ruebenstahl, A. A., O’Connor, J. K., Bhullar, B.-A. S., & Norell, M. A.
- Affiliations
- North Carolina Museum of Natural Sciences (US)
- Johns Hopkins University (US)
- Yale University (US)
- American Museum of Natural History (US)
- Corresponding author
- Napoli, James G.
- ORCID
- Venue
- Nature
- Published
- 2025-07-09
- Volume
- 644
- Issue
- 8077
- Pages
- 699-705
- ISSN
- 0028-0836 (ISSN-L)
- 1476-4687
- OpenAlex
- W4412151432
- Cited by
- 17
- References
- 0
- Citations by year
- 2026: 14 · 2025: 3
- FWCI
- 11.98
- Type
- journal article
- Language
- en
- Open access
- closed
- Licence
- Locations
- Nature (publishedVersion)
- PubMed (publishedVersion)
- Topics
- Physical Sciences › Earth and Planetary Sciences › Paleontology › Paleontology and Evolutionary Biology
- Physical Sciences › Earth and Planetary Sciences › Paleontology › Evolution and Paleontology Studies
- Health Sciences › Medicine › Urology › Comparative Animal Anatomy Studies
- Keywords
- theropod dinosaurs, wrist, pisiform bone, Oviraptorosauria, Troodontidae, wing kinematics, Microraptor, Late Cretaceous
- MeSH terms
- Animals, Birds, Biological Evolution, Flight, Animal, Forelimb, Fossils, Phylogeny, Wings, Animal, Dinosaurs
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