Archaeopteryx feather sheaths reveal sequential center-out flight-related molting strategy

Thomas G Kaye,William R Wahl,Michael Pittman

doi:10.1038/s42003-020-01467-2

Thomas G Kaye, William R Wahl + Show 1 more

Open Access

https://doi.org/10.1038/s42003-020-01467-2

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Abstract

Modern flying birds molt to replace old and worn feathers that inhibit flight performance, but its origins are unclear. We address this by presenting and evaluating a ~150 million year old record of molting in a feathered dinosaur from the early bird Archaeopteryx. Laser-Stimulated Fluorescence revealed feather sheaths that are otherwise invisible under white light. These are separated by one feather and are not in numerical sequential order and are mirrored in both wings. This indicates that a sequential center-out molting strategy was already present at the origins of flight, which is used in living falcons to preserve maximum flight performance. This strategy would have been a welcome advantage for early theropod flyers that had poor flight capabilities. This discovery provides important insights into how birds refined their early flight capabilities before the appearance of the keeled sternum, pygostyle and triosseal canal.

Highlights

Modern flying birds molt to replace old and worn feathers that inhibit flight performance, but its origins are unclear
The sequential molt in Microraptor and molting data in extant birds was used by Kiat et al.[10] to suggest that sequential molting is the outcome of evolutionary forces to maintain flight capability throughout the entire annual cycle in both extant birds and nonavialan paravian theropods[10]
In this study we identify the earliest evidence of pennaraptoran feather molting to our knowledge and discuss its implications on the origins of flight-related molting and of flight

Summary

Introduction

Modern flying birds molt to replace old and worn feathers that inhibit flight performance, but its origins are unclear. These are separated by one feather and are not in numerical sequential order and are mirrored in both wings This indicates that a sequential center-out molting strategy was already present at the origins of flight, which is used in living falcons to preserve maximum flight performance. The second strategy is a center-out approach where a center feather is lost first and subsequent feathers are shed outwards from this center point; this is more common in non-passerine birds such as falcons[5] This minimizes the size of the aerodynamic hole in the wing, which allows falcons to better maintain their flight performance for hunting[3,6]. In this study we identify the earliest evidence of pennaraptoran feather molting to our knowledge and discuss its implications on the origins of flight-related molting and of flight

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