[dinosaur] Juvenile enantiornithines with immature feathers (free pdf)

Ben Creisler
[email protected]

A new paper with free pdf:

Jingmai K. O’CONNOR, Amanda FALK, WANG Min & ZHENG Xiao-Ting (2019)
First report of immature feathers in juvenile enantiornithines from the
Early Cretaceous Jehol avifauna.
Vertebrata PalAsiatica (advance online publication)
DOI: 10.19615/j.cnki.1000-3118.190823
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Free pdf:
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Molting--the process replacing one plumage with another--is a critically
important biological function in Aves. This process annually replaces the
feather coat, damaged by normal wear and tear, produces ontogenetic changes
in feathering, and produces alternate breeding plumages associated with
reproductive activity in adults. Immature, growing feathers are encased in
a keratinous sheath, giving them a narrow, tubular, and featureless
appearance. The complete loss of the sheath indicates the feather is
mature. Despite the wealth of integumentary data published from the Jehol
Biota, immature feathers have never been definitively reported, although
they may potentially be preserved in a juvenile specimen of the non-avian
oviraptorosaur theropod dinosaur Similicaudipteryx from the 120 Ma
Jiufotang Formation. A developing feather has been reported in a 99 Ma
enantiornithine neonate preserved in Burmese amber, in which
three-dimensional preservation makes interpretations of integumentary
structures more straightforward. Here we report on probable immature
feathers in four juvenile enantiornithines (Aves: Ornithothoraces) from the
Jehol Group. As observed in developing feathers in extant birds, the
purported immature fossil feathers appear proximally narrow and featureless
with barbs protruding only distally. Based on our observations, we suggest
that similar-appearing feather structures preserved on the manus and
tibiotarsus in the holotype of the enantiornithine Cruralispennia
multidonta may alternatively be interpreted as immature feathers. The
presence of immature feathers in combination with sexually dimorphic
ornamental feathers in juvenile enantiornithines suggests the complex
molting patterns of Neornithes, in which such ornaments only appear after
several years (following several molts) when reproductive activity is
achieved, are limited to a subset of crownward avians.

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