<abstract xmlns="http://www.w3.org/1999/xhtml">

<p>There is increasing interest from evolutionary biologists in the evolution of avian bill shape, how the bill is used during feeding and, in particular, the bite forces the bill can deliver. Bite force exhibits isometry with the total mass of the jaw musculature, but there is variation in the functional categories of the jaw muscles in different avian taxa. Qualitative descriptions of the jaw musculature do not allow analysis of the relative contributions that adductor or retractor muscles play in generating a bite force. This study is a meta-analysis of published data for body mass and the mass of the jaw musculature in 66 bird species from 10 orders. The masses of the different muscles contributing to adduction and retraction in closing the jaw, and to depression and protraction in opening the jaw, were summed and allometric relationships explored before investigating the effects of taxonomic order on these relationships. The categories of muscles, and the masses of each category of jaw musculature varied among avian orders. Some species, such as the flightless ratites, had relatively small jaw muscle mass but parrots had an additional adductor muscle. Phylogenetically controlled relationships between body mass and the mass of each muscle category irrespective of taxonomic order were isometric. However, analysis of covariance revealed significant interactions between body mass and taxonomic order. Most orders had low values for body-mass-specific muscle masses in the jaw with the notable exceptions of the Passeriformes (songbirds) and Psittaciformes (parrots). The values of these orders were 3–4 times greater, although the relative amounts of muscles contributing to adduction and retraction were similar in Psittaciformes, but adduction was markedly higher in Passeriformes. The results of these analyses highlight the lack of species-specific data for most birds, which is adversely impacting our understanding of the anatomical features that are determining the functional properties of the bill during feeding.</p>
</abstract>

There is increasing interest from evolutionary biologists in the evolution of avian bill shape, how the bill is used during feeding and, in particular, the bite forces the bill can deliver. Bite force exhibits isometry with the total mass of the jaw musculature, but there is variation in the functional categories of the jaw muscles in different avian taxa. Qualitative descriptions of the jaw musculature do not allow analysis of the relative contributions that adductor or retractor muscles play in generating a bite force. This study is a meta-analysis of published data for body mass and the mass of the jaw musculature in 66 bird species from 10 orders. The masses of the different muscles contributing to adduction and retraction in closing the jaw, and to depression and protraction in opening the jaw, were summed and allometric relationships explored before investigating the effects of taxonomic order on these relationships. The categories of muscles, and the masses of each category of jaw musculature varied among avian orders. Some species, such as the flightless ratites, had relatively small jaw muscle mass but parrots had an additional adductor muscle. Phylogenetically controlled relationships between body mass and the mass of each muscle category irrespective of taxonomic order were isometric. However, analysis of covariance revealed significant interactions between body mass and taxonomic order. Most orders had low values for body-mass-specific muscle masses in the jaw with the notable exceptions of the Passeriformes (songbirds) and Psittaciformes (parrots). The values of these orders were 3–4 times greater, although the relative amounts of muscles contributing to adduction and retraction were similar in Psittaciformes, but adduction was markedly higher in Passeriformes. The results of these analyses highlight the lack of species-specific data for most birds, which is adversely impacting our understanding of the anatomical features that are determining the functional properties of the bill during feeding.

Effects of body mass and taxonomic order on the masses of functionally classified groups of the jaw musculature in birds

Department of Life Sciences, School of Life and Environmental Sciences

University of Lincoln, Joseph Banks Laboratories

Ornis Hungarica

This work is licensed under the Creative Commons Attribution-NonCommercial-NoDerivatives 4.0 International License.

There is increasing interest from evolutionary biologists in the evolution of avian bill shape, how the bill is used during feeding and, in particular, the...

Effects of body mass and taxonomic order on the masses of functionally classified groups of the jaw musculature in birds

Published Online: Jun 12, 2024

Page range: 45 - 60

Received: Apr 11, 2024

Accepted: May 12, 2024

DOI: https://doi.org/10.2478/orhu-2024-0004

Keywords
anatomy, jaw, adductor muscles, allometry, depressor muscles, protractor muscles, retractor muscles

© 2024 D. Charles Deeming et al., published by Sciendo

This work is licensed under the Creative Commons Attribution-NonCommercial-NoDerivatives 4.0 International License.

Effects of body mass and taxonomic order on the masses of functionally classified groups of the jaw musculature in birds

Published Online: Jun 12, 2024

Page range: 45 - 60

Received: Apr 11, 2024

Accepted: May 12, 2024

DOI: https://doi.org/10.2478/orhu-2024-0004

Keywordsanatomy, jaw, adductor muscles, allometry, depressor muscles, protractor muscles, retractor muscles

© 2024 D. Charles Deeming et al., published by Sciendo

This work is licensed under the Creative Commons Attribution-NonCommercial-NoDerivatives 4.0 International License.

Keywords
anatomy, jaw, adductor muscles, allometry, depressor muscles, protractor muscles, retractor muscles