Theropod wrist reorganization before avian flight
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Ben Creisler
Jul 9, 2025, 11:55:07 AM7/9/25
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Ben Creisler
The curious case of how bird wrists evolved
Wrist evolution helped birds to conquer the air. Fossil data and analysis of a modern bird’s development reveal that this evolution preceded bird origins
A new paper:
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James G. Napoli, Matteo Fabbri, Alexander A. Ruebenstahl, Jingmai K. O’Connor, Bhart-Anjan S. Bhullar & Mark A. Norell (2025)
Reorganization of the theropod wrist preceded the origin of avian flight
Nature (advance online publication)
doi: https://doi.org/10.1038/s41586-025-09232-3
https://www.nature.com/articles/s41586-025-09232-3
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). The pisiform plays a crucial role in stabilization of the distal wingtip during flight, and facilitates kinematic integration that ‘automates’ wing motion. 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. 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, Ambopteryx and Anchiornis. 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. 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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James G. Napoli, Matteo Fabbri, Alexander A. Ruebenstahl, Jingmai K. O’Connor, Bhart-Anjan S. Bhullar & Mark A. Norell (2025)
Reorganization of the theropod wrist preceded the origin of avian flight
Nature (advance online publication)
doi: https://doi.org/10.1038/s41586-025-09232-3
https://www.nature.com/articles/s41586-025-09232-3
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). The pisiform plays a crucial role in stabilization of the distal wingtip during flight, and facilitates kinematic integration that ‘automates’ wing motion. 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. 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, Ambopteryx and Anchiornis. 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. 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.
****
The curious case of how bird wrists evolved
Wrist evolution helped birds to conquer the air. Fossil data and analysis of a modern bird’s development reveal that this evolution preceded bird origins
Ben Creisler
Jul 9, 2025, 4:58:52 PM7/9/25
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News:
This wrist’s twist is its link between dinosaurs and birds
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