Birds: carina size and sternum morphology relationship + pectoralis muscle orientation and flapping ability (free pdfs)
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Ben Creisler
Jun 18, 2026, 1:52:21 PM (12 hours ago) Jun 18
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Ben Creisler
Recent avian papers:
D. C. Deeming (2026)
Relationship between carina size and sternum morphology in birds reflects physical constraints of body size and flight style
Journal of Anatomy (advance online publication)
doi: https://doi.org/10.1111/joa.70190
https://onlinelibrary.wiley.com/doi/10.1111/joa.70190
The avian sternum is the largest bone in the body to accommodate the large muscles required for flight. Previous analysis showed that variation in keel and sternum morphology only weakly reflected body size and flight style and implied that variation in caudal metasternum morphology was associated with expansion of bony trabeculae in some species. This study used area measurements to explore the idea that, to minimise body mass, variation in keel size was inversely correlated with variation in the shape of the metasternum. Data for sternum dimensions and area were collected from digital images of pectoral girdles and the sternum in articulation of 62 species representing 10 different orders. The keel area was expressed as a proportion of the total sternum area, and the area of the sternum from the ventral aspect occupied by bone was expressed as a proportion of the assumed maximum possible bone area. Phylogenetically controlled linear modelling explored the effects of body mass, order, sternum type and flight style. Sternum area and keel area exhibited isometric relationships with body mass which had different intercepts for each order. Proportional keel area was inversely related to body mass in some but not all orders. The proportional bone area exhibited a positive relationship with body mass and there was a significant effect of order. Proportional keel area exhibited a negative relationship with the proportional bone area. Both sternum type and flight style significantly affected proportional keel area and the proportional bone area. It was concluded that to save body mass, an increase in bone mass associated with the development of a keel has been mitigated by bone not developing (rather than extension of existing bone) in the caudal metasternum. Such patterns would also explain observed variation in sternum morphology in Mesozoic birds.
Free pdf:
Takumi Akeda & Shin-ichi Fujiwara (2026)
The pectoralis muscle orientation as an indicator of the modes of wing-propelled locomotion in birds
Free pdf:
D. C. Deeming (2026)
Relationship between carina size and sternum morphology in birds reflects physical constraints of body size and flight style
Journal of Anatomy (advance online publication)
doi: https://doi.org/10.1111/joa.70190
https://onlinelibrary.wiley.com/doi/10.1111/joa.70190
The avian sternum is the largest bone in the body to accommodate the large muscles required for flight. Previous analysis showed that variation in keel and sternum morphology only weakly reflected body size and flight style and implied that variation in caudal metasternum morphology was associated with expansion of bony trabeculae in some species. This study used area measurements to explore the idea that, to minimise body mass, variation in keel size was inversely correlated with variation in the shape of the metasternum. Data for sternum dimensions and area were collected from digital images of pectoral girdles and the sternum in articulation of 62 species representing 10 different orders. The keel area was expressed as a proportion of the total sternum area, and the area of the sternum from the ventral aspect occupied by bone was expressed as a proportion of the assumed maximum possible bone area. Phylogenetically controlled linear modelling explored the effects of body mass, order, sternum type and flight style. Sternum area and keel area exhibited isometric relationships with body mass which had different intercepts for each order. Proportional keel area was inversely related to body mass in some but not all orders. The proportional bone area exhibited a positive relationship with body mass and there was a significant effect of order. Proportional keel area exhibited a negative relationship with the proportional bone area. Both sternum type and flight style significantly affected proportional keel area and the proportional bone area. It was concluded that to save body mass, an increase in bone mass associated with the development of a keel has been mitigated by bone not developing (rather than extension of existing bone) in the caudal metasternum. Such patterns would also explain observed variation in sternum morphology in Mesozoic birds.
=====
Free pdf:
Takumi Akeda & Shin-ichi Fujiwara (2026)
The pectoralis muscle orientation as an indicator of the modes of wing-propelled locomotion in birds
Journal of Anatomy (advance online publication)
doi: https://doi.org/10.1111/joa.70196
https://onlinelibrary.wiley.com/doi/10.1111/joa.70196
Free pdf:
https://onlinelibrary.wiley.com/doi/epdf/10.1111/joa.70196
Given the diversification of wingbeat utilisation for body propulsion among birds, it is essential to understand the relationship between skeletal morphology and flapping ability, depending on the wing depression exerted by the pectoralis muscle. The path between the origin and insertion of the pectoralis, which can be identified on the skeletal surface, indicates the orientation of the force it exerts. In this study, line segments were made within the pectoralis to represent the lines of muscle action (LoA). We then compared their overall orientation and distribution among different modes of wing-propelled locomotion (WPL) using three-dimensional skeletal models constructed from computed tomography and surface scans of 79 neornithine bird specimens. The species were selected to represent a diverse range of taxonomic groups, WPL modes, and body masses. The pectoralis LoAs in flap-flight and wing-propelled diving birds were oriented craniolaterally, whereas those in soaring birds were oriented more laterally. These differences in pectoralis profiles among species suggest a putative adaptation to generate forces more efficiently in the direction necessary for typical flapping styles. Therefore, the overall morphology of the thoracic skeleton, which reflects pectoral muscle orientation, can be an indicator of WPL mode. It can also be utilised as a more robust approach for reconstructing the locomotor capabilities of fossil taxa with avian-like musculoskeletal systems.
doi: https://doi.org/10.1111/joa.70196
https://onlinelibrary.wiley.com/doi/10.1111/joa.70196
Free pdf:
https://onlinelibrary.wiley.com/doi/epdf/10.1111/joa.70196
Given the diversification of wingbeat utilisation for body propulsion among birds, it is essential to understand the relationship between skeletal morphology and flapping ability, depending on the wing depression exerted by the pectoralis muscle. The path between the origin and insertion of the pectoralis, which can be identified on the skeletal surface, indicates the orientation of the force it exerts. In this study, line segments were made within the pectoralis to represent the lines of muscle action (LoA). We then compared their overall orientation and distribution among different modes of wing-propelled locomotion (WPL) using three-dimensional skeletal models constructed from computed tomography and surface scans of 79 neornithine bird specimens. The species were selected to represent a diverse range of taxonomic groups, WPL modes, and body masses. The pectoralis LoAs in flap-flight and wing-propelled diving birds were oriented craniolaterally, whereas those in soaring birds were oriented more laterally. These differences in pectoralis profiles among species suggest a putative adaptation to generate forces more efficiently in the direction necessary for typical flapping styles. Therefore, the overall morphology of the thoracic skeleton, which reflects pectoral muscle orientation, can be an indicator of WPL mode. It can also be utilised as a more robust approach for reconstructing the locomotor capabilities of fossil taxa with avian-like musculoskeletal systems.
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