[dinosaur] Cretaceous extinct rachis-dominated feathers in amber (free pdf)

Ben Creisler
[email protected]


A new paper in open access


Nathan R. Carroll, Luis M. Chiappe & David J. Bottjer (2019)
Mid-Cretaceous amber inclusions reveal morphogenesis of extinct
rachis-dominated feathers
Scientific Reports 9, Article number: 18108
DOI: https://urldefense.proofpoint.com/v2/url?u=https-3A__doi.org_10.1038_s41598-2D019-2D54429-2Dy&d=DwIFaQ&c=clK7kQUTWtAVEOVIgvi0NU5BOUHhpN0H8p7CSfnc_gI&r=Ry_mO4IFaUmGof_Yl9MyZgecRCKHn5g4z1CYJgFW9SI&m=IZr98hLzMSQxoa--rNd77U4huEsHXEHEO4N5U2w-3NU&s=tZioddkftc-ZuT63pzWAfL-kNON-K0kjxRJZYuQ5d7s&e= 
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We describe three-dimensionally preserved feathers in mid-Cretaceous
Burmese amber that share macro-morphological similarities (e.g.,
proportionally wide rachis with a “medial stripe”) with lithic,
two-dimensionally preserved rachis-dominated feathers, first recognized in
the Jehol Biota. These feathers in amber reveal a unique ventrally concave
and dorsoventrally thin rachis, and a dorsal groove (sometimes pigmented)
that we identify as the “medial stripe” visible in many rachis-dominated
rectrices of Mesozoic birds. The distally pennaceous portion of these
feathers shows differentiated proximal and distal barbules, the latter with
hooklets forming interlocking barbs. Micro-CT scans and transverse sections
demonstrate the absence of histodifferentiated cortex and medullary pith of
the rachis and barb rami. The highly differentiated barbules combined with
the lack of obvious histodifferentiation of the barb rami or rachis
suggests that these feathers could have been formed without the full suite
and developmental interplay of intermediate filament alpha keratins and
corneous beta-proteins that is employed in the cornification process of
modern feathers. This study thus highlights how the development of these
feathers might have differed from that of their modern counterparts, namely
in the morphogenesis of the ventral components of the rachis and barb rami.
We suggest that the concave ventral surface of the rachis of these
Cretaceous feathers is not homologous with the ventral groove of modern
rachises. Our study of these Burmese feathers also confirms previous
claims, based on two-dimensional fossils, that they correspond to an
extinct morphotype and it cautions about the common practice of
extrapolating developmental aspects (and mechanical attributes) of modern
feathers to those of stem birds (and their dinosaurian outgroups) because
the latter need not to have developed through identical pathways.