Molecular composition and ultrastructure of Jurassic paravian feathers.

Johan Lindgren,François Escuillié,Jimmy Heimdal,Aude Cincotta,Per Uvdal,Peter Sjövall,Anders Engdahl,Ola Gustafsson,Ulysse Lefèvre,Johan Yans,Kazumasa Wakamatsu,Steven W Hutcheson,Benjamin P Kear,Johan A Gren,Pascal Godefroit,Ryan M Carney

doi:10.1038/srep13520

Abstract

Feathers are amongst the most complex epidermal structures known, and they have a well-documented evolutionary trajectory across non-avian dinosaurs and basal birds. Moreover, melanosome-like microbodies preserved in association with fossil plumage have been used to reconstruct original colour, behaviour and physiology. However, these putative ancient melanosomes might alternatively represent microorganismal residues, a conflicting interpretation compounded by a lack of unambiguous chemical data. We therefore used sensitive molecular imaging, supported by multiple independent analytical tests, to demonstrate that the filamentous epidermal appendages in a new specimen of the Jurassic paravian Anchiornis comprise remnant eumelanosomes and fibril-like microstructures, preserved as endogenous eumelanin and authigenic calcium phosphate. These results provide novel insights into the early evolution of feathers at the sub-cellular level, and unequivocally determine that melanosomes can be preserved in fossil feathers.

Highlights

Initially classified as a non-avian troodontid theropod[1], recent studies suggest that Anchiornis represents a stem avialan, more primitive than Archaeopteryx[4,23]
Some integument residues were lost during preparation; patches of feathers and feather-like structures extend along the back half of the skull, lateral to the shoulder girdle, above the pelvic girdle, and along the forelimbs, hind limbs and tail (Fig. 1a,b)
The sample was considered optimal for investigation because: (1) it showed greyish-brownish colouration indicative of organic remains; (2) was uncovered from a ‘fresh’ sub-surface layer within the sedimentary matrix; (3) produced part and counterpart sub-samples that revealed internal structuring of the filamentous epidermal appendages (Supplementary Fig. S1); and (4) similar ‘crest’ feathers from another Anchiornis fossil have been interpreted as housing pheomelanosomes[5]; that is, spheroid melanosomes dominated by pheomelanin pigment[25]

Summary

Introduction

This centres on the observation that microbes colonising the epidermal tissues during decay are virtually indistinguishable from the melanosome-like microbodies recognised in fossils[14,15]. Such criticism is aggravated by the lack of unequivocal molecular traces from melanic pigments in ancient feathers and feather-like appendages[15,16]. We address the unresolved problem of accurately identifying microbodies, imprints and fibrous structures associated with fossilised feather remains via high-resolution imaging and molecular analysis of an exceptionally preserved new specimen (YFGP-T5199, housed in Yizhou Fossil and Geology Park) of the paravian Anchiornis[22]. Our results show that multiple local taphonomic pathways incorporating both organic and geochemical agents contributed to the retention of fibrils, eumelanin pigment and eumelanosomes in the integumentary filaments of YFGP-T5199

Methods

Results

Conclusion