Abstract
It was previously suggested that the flight ability of feathered fossils could be hypothesized from the diameter of their feather rachises. Central to the idea is the unvalidated assumption that the strength of a primary flight feather (i.e. its material and structural properties) may be consistently calculated from the external diameter of the feather rachis, which is the only dimension that is likely to relate to structural properties available from fossils. Here, using three-point bending tests, the relationship between feather structural properties (maximum bending moment, Mmax and Young's modulus, Ebend) and external morphological parameters (primary feather rachis length, diameter and second moment of area at the calamus) in 180 primary feathers from four species of bird of differing flight style was investigated. Intraspecifically, both Ebend and Mmax were strongly correlated with morphology, decreasing and increasing, respectively, with all three morphological measures. Without accounting for species, however, external morphology was a poor predictor of rachis structural properties, meaning that precise determination of aerial performance in extinct, feathered species from external rachis dimensions alone is not possible. Even if it were possible to calculate the second moment of area of the rachis, our data suggest that feather strength could still not be reliably estimated.
Highlights
It was previously suggested that the flight ability of feathered fossils could be hypothesized from the diameter of their feather rachises
Central to the idea is the unvalidated assumption that the strength of a primary flight feather may be consistently calculated from the external diameter of the feather rachis, which is the only dimension that is likely to relate to structural properties available from fossils
Narrow Ør suggested that these species were not capable of the flapping flight seen in extant birds assuming similar hollow feather rachis morphology
Summary
It was previously suggested that the flight ability of feathered fossils could be hypothesized from the diameter of their feather rachises. Using three-point bending tests, the relationship between feather structural properties (maximum bending moment, Mmax and Young’s modulus, Ebend) and external morphological parameters (primary feather rachis length, diameter and second moment of area at the calamus) in 180 primary feathers from four species of bird of differing flight style was investigated. Both Ebend and Mmax were strongly correlated with morphology, decreasing and increasing, respectively, with all three morphological measures. Feather failure moments and their correlation with feather morphology are critical in any assessment of flight capabilities of extinct species and are currently lacking
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