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. 2023 Feb 23;9(1):4.
doi: 10.1186/s40851-023-00204-x.

Origin of the propatagium in non-avian dinosaurs

Yurika Uno, Tatsuya Hirasawa  1
Affiliations

Origin of the propatagium in non-avian dinosaurs

Yurika Uno et al. Zoological Lett. .

Abstract

Avian wings as organs for aerial locomotion are furnished with a highly specialized musculoskeletal system compared with the forelimbs of other tetrapod vertebrates. Among the specializations, the propatagium, which accompanies a skeletal muscle spanning between the shoulder and wrist on the leading edge of the wing, represents an evolutionary novelty established at a certain point in the lineage toward crown birds. However, because of the rarity of soft-tissue preservation in the fossil record, the evolutionary origin of the avian propatagium has remained elusive. Here we focus on articulated skeletons in the fossil record to show that angles of elbow joints in fossils are indicators of the propatagium in extant lineages of diapsids (crown birds and non-dinosaurian diapsids), and then use this relationship to narrow down the phylogenetic position acquiring the propatagium to the common ancestor of maniraptorans. Our analyses support the hypothesis that the preserved propatagium-like soft tissues in non-avian theropod dinosaurs (oviraptorosaurian Caudipteryx and dromaeosaurian Microraptor) are homologous with the avian propatagium, and indicate that all maniraptoran dinosaurs likely possessed the propatagium even before the origin of flight. On the other hand, the preserved angles of wrist joints in non-avian theropods are significantly greater than those in birds, suggesting that the avian interlocking wing-folding mechanism involving the ulna and radius had not fully evolved in non-avian theropods. Our study underscores that the avian wing was acquired through modifications of preexisting structures including the feather and propatagium.

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Conflict of interest statement

The authors declare that they have no competing interests.

Figures

Fig. 1
Fig. 1
Musculoskeletal system of the avian left wing in ventral view. A, B, Propatagium (A) and forelimb muscles (B). C, D, Synchronous actions between the elbow and wrist joints, at an extension via the function of the musculus (m.) propatagialis (C) and at a flexion via the interlocking wing-folding system (D)
Fig. 2
Fig. 2
Soft-tissue preservations of putative propatagia in non-avian theropods. A Microraptor gui (IVPP V 13352). B–D, Caudipteryx sp. (IVPP V 12430). C and D represent the enlarged image and line drawing of the area of the white box in B, respectively. Broken lines in D indicate missing borders of the soft tissues. d1–3, digits 1–3; f, feather; g, gastralium; ppt, propatagium; r, radius; u, ulna
Fig. 3
Fig. 3
Comparison of preserved elbow and wrist-joint angles between the non-dinosaurian diapsids and crown birds. A Elbow-joint angles. B Wrist-joint angles. Measurements were obtained from 71 non-dinosaurian diapsid and 35 crown bird articulated fossil skeletons
Fig. 4
Fig. 4
Evolutionary process of the propatagium. The evolutionary process of the propatagium was inferred based on the elbow-joint angles preserved in fossils (evidence for absence) and soft-tissue preservation (evidence for presence)
Fig. 5
Fig. 5
The “intermediate” and avian-state morphotypes. A Deinonychus antirrhopus representing the “intermediate” morphotype. The propatagium was present, while the wrist could extend toward the radial side in a grasping movement. B Sapeornis chaoyangensis with the avian interlocking wing-folding system
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References

    1. Prum RO. Development and evolutionary origin of feathers. J Exp Zool. 1999;285:291–306. doi: 10.1002/(SICI)1097-010X(19991215)285:4<291::AID-JEZ1>3.0.CO;2-9. - DOI - PubMed
    1. Xu X, Zheng X, You H. Exceptional dinosaur fossils show ontogenetic development of early feathers. Nature. 2010;464:1338–1341. doi: 10.1038/nature08965. - DOI - PubMed
    1. O’Connor PM, Claessens LPAM. Basic avian pulmonary design and flow-through ventilation in non-avian theropod dinosaurs. Nature. 2005;436:253–256. doi: 10.1038/nature03716. - DOI - PubMed
    1. Balanoff AM, Bever GS, Rowe TB, Norell MA. Evolutionary origins of the avian brain. Nature. 2013;501:93–96. doi: 10.1038/nature12424. - DOI - PubMed
    1. Organ CL, Shedlock AM, Meade A, Pagel M, Edwards SV. Origin of avian genome size and structure in non-avian dinosaurs. Nature. 2007;446:180–184. doi: 10.1038/nature05621. - DOI - PubMed

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