The primary feather lengths of early birds with respect to avian wing shape evolution.

We examine the relationships between primary feather length (f(prim)) and total arm length (ta) (sum of humerus, ulna and manus lengths) in Mesozoic fossil birds to address one aspect of avian wing shape evolution. Analyses show that there are significant differences in the composition of the wing between the known lineages of basal birds and that mean f(prim) (relative to ta length) is significantly shorter in Archaeopteryx and enantiornithines than it is in Confuciusornithidae and in living birds. Based on outgroup comparisons with nonavian theropods that preserve forelimb primary feathers, we show that the possession of a relatively shorter f(prim) (relative to ta length) must be the primitive condition for Aves. There is also a clear phylogenetic trend in relative primary feather length throughout bird evolution: our analyses demonstrate that the f(prim)/ta ratio increases among successive lineages of Mesozoic birds towards the crown of the tree ('modern birds'; Neornithes). Variance in this ratio also coincides with the enormous evolutionary radiation at the base of Neornithes. Because the f(prim)/ta ratio is linked to flight mode and performance in living birds, further comparisons of wing proportions among Mesozoic avians will prove informative and certainly imply that the aerial locomotion of the Early Cretaceous Confuciusornis was very different to other extinct and living birds.

Wang X ，Nudds RL ，Dyke GJ 《-》

Narrow primary feather rachises in Confuciusornis and Archaeopteryx suggest poor flight ability.

Nudds RL ，Dyke GJ 《-》

Size scaling and stiffness of avian primary feathers: implications for the flight of Mesozoic birds.

The primary feathers of birds are subject to cyclical forces in flight causing their shafts (rachises) to bend. The amount the feathers deflect during flight is dependent upon the flexural stiffness of the rachises. By quantifying scaling relationships between body mass and feather linear dimensions in a large data set of living birds, we show that both feather length and feather diameter scale much closer to predictions for geometric similarity than they do to elastic similarity. Scaling allometry also indicates that the primary feathers of larger birds are relatively shorter and their rachises relatively narrower, compared to those of smaller birds. Two-point bending tests indicated that larger birds have more flexible feathers than smaller species. Discriminant functional analyses (DFA) showed that body mass, primary feather length and rachis diameter can be used to differentiate between different magnitudes of feather bending stiffness, with primary feather length explaining 63% of variance in rachis stiffness. Adding fossil measurement data to our DFA showed that Archaeopteryx and Confuciusornis do not overlap with extant birds. This strongly suggests that the bending stiffness of their primary feathers was different to extant birds and provides further evidence for distinctive flight styles and likely limited flight ability in Archaeopteryx and Confuciusornis.

Wang X ，Nudds RL ，Palmer C ，Dyke GJ ... -  《-》

Comment on "Narrow primary feather rachises in Confuciusornis and Archaeopteryx suggest poor flight ability".

Zheng X ，Xu X ，Zhou Z ，Miao D ，Zhang F ... -  《-》

Comment on "Narrow primary feather rachises in Confuciusornis and Archaeopteryx suggest poor flight ability".

Paul GS 《-》