Conceived and designed the experiments: XW AM GD. Performed the experiments: XW AM GD. Analyzed the data: XW AM GD. Contributed reagents/materials/analysis tools: XW AM GD. Wrote the paper: XW AM GD.
The authors have declared that no competing interests exist.
We investigated the relationship between wing element proportions and flight mode in a dataset of living avian species to provide a framework for making basic estimates of the range of flight styles evolved by Mesozoic birds. Our results show that feather length (
The timing and sequence of events that led to the origin and subsequent evolution of flapping flight in birds remains an important unanswered question in vertebrate evolutionary biology. Despite a substantial increase in the numbers of early birds discovered and described, including exceptionally well-preserved dinosaurs with feathers, the single largest impediment to interpreting the flight adaptations of a fossil is the common absence of a preserved wing outline
A ‘functional wing’ (total arm,
Research that relates wing morphology to different flight modes among extant birds has been limited; Rayner (1988)
Most recently, Simons
Here, we analyze a large sample of wing component measurements (including primary feathers) from extant and Mesozoic fossil bird groups. Our aim is to assess whether the proportions of the living avian wing are robust predictors of flight style that can then be applied to fossil taxa. Our specific objectives are: (1) to investigate the relationship between wing element proportions and flight modes across a wide range of living species; and (2) provide basic estimates for the range of flight styles used by Mesozoic birds based on parameters derived from our analyses of extant taxa.
“Living birds” here refers to museum specimens of extant Neornithes (not live birds) from the Natural History collections of the National Museum, Ireland. Mesozoic bird measurements we use were collected from fossil specimens in Chinese museums, as follows: Institute of Vertebrate Paleontology and Paleoanthropology (Beijing) and Shandong Tianyu Museum of Nature (Pingyi). Permission was granted by these institutions for specimen access and measurements.
Measurements of wing bones and primary feathers were taken for a sample of living and Mesozoic birds (
Four flight styles for living birds were used:‘continuous flapping’ (CF) (e.g. grebes, ducks and auks); ‘flapping and soaring’ (FS) (e.g. storks, pelicans and large raptors); ‘flapping and gliding’ (FG) (e.g. swifts, falcons and gulls); ‘passerine-type flight’ (PT). These styles were coded for our living bird sample, as defined (and analyzed) by Bruderer
Given the large number of comparisons, Hochberg multiple comparisons tests (HMCT) were used
One-way ANOVA and Kruskal-Wallis non-parametric tests show that
Although our focus here is on the
Both PCA and DFA (with four wing measurements included) can broadly discriminate between the four flight styles, but neither technique perfectly replicates the groupings (
(a) Principal component analysis (PCA) showed by (PC) 1 and 2.
As our analyses show that
CF, ‘continuous flapping’; FS, ‘flapping and soaring’; FG, ‘flapping and gliding’; PT, ‘passerine-type flight’; Ar (
1,‘continuous flapping’; 2, ‘flapping and soaring’; 3, ‘flapping and gliding’; 4, ‘passerine-type flight’; 5,
‘CF’ | ‘FS’ | ‘FG’ | ‘PT’ | |
|
0 | 0 | 0 | 0 |
|
0 | 0 | 0 | 0 |
Enantiornithines | 21.4% | 7.1% | 0 | 0 |
Ornithurae | 25% | 0 | 0 | 0 |
CF, ‘continuous flapping’; FS, ‘flapping and soaring’; FG, ‘flapping and gliding’; PT, ‘passerine-type flight’.
PCA | DFA | ||
|
/ | / | / |
|
‘FG’ | ‘CF’ | / |
Enantiornithines | ‘FG’ | ‘CF’, ‘FS’, ‘PT’ | ‘CF’, ‘FS’ |
Ornithurae | ‘CF’, ‘PT’ | ‘CF’ | ‘CF’ |
In summary, our results suggest that: (1)
Comparisons of
A range of statistical and ordination techniques show that lengths of wing elements (
After controlling for body size,
Considering that the edge of the manus is the main attachment site for the primary feathers and the region of the airfoil surface that mediates drag and lift during flapping, we agree with Nudds
Our data show quantitatively that
Analysis of PCA, DFA and
Nevertheless, both PCA and DFA results show that the flight style of
The finding that enantiornithines plot across all the flight styles of living birds is in accordance with surveys that have shown the forelimb proportions of these birds to also fall within the range of extant taxa
Ornithurine birds are anatomically critical to understanding the later stages in the evolution of flapping flight because representatives of this lineage show development of a fused hand wing (carpometacarpus) for the first time
In sum, our analysis show that the
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We thank Xiaoting Zheng and Zhonghe Zhou for collections access in China. We thank Lars Schmidt, Jingmai O'Connor and an anonymous referee for helpful comments that improved the clarity of this paper.