Suchergebnisse

Abstract
Colors are well studied in bird plumage but not in other integumentary structures. In particular, iridescent colors from structures other than plumage are undescribed in birds. Here, we show that a multilayer of keratin and lipids is sufficient to produce the iridescent bill of Spermophaga haematina. Furthermore, that the male bill is presented to the female under different angles during display provides support for the hypothesis that iridescence evolved in response to sexual selection. This is the first report of an iridescent bill, and only the second instance of iridescence in birds in which melanosomes are not involved. Furthermore, an investigation of museum specimens of an additional 98 species, showed that this evolved once, possibly twice. These results are promising, as they suggest that birds utilize a wider array of physical phenomena to produce coloration and should further stimulate research on nonplumage integumentary colors.

Remarkably well-preserved soft tissues in Mesozoic fossils have yielded substantial insights into the evolution of feathers(1). New evidence of branched feathers in pterosaurs suggests that feathers originated in the avemetatarsalian ancestor of pterosaurs and dinosaurs in the Early Triassic(2), but the homology of these pterosaur structures with feathers is controversial(3,4). Reports of pterosaur feathers with homogeneous ovoid melanosome geometries(2,5) suggest that they exhibited limited variation in colour, supporting hypotheses that early feathers functioned primarily in thermoregulation(6). Here we report the presence of diverse melanosome geometries in the skin and simple and branched feathers of a tapejarid pterosaur from the Early Cretaceous found in Brazil. The melanosomes form distinct populations in different feather types and the skin, a feature previously known only in theropod dinosaurs, including birds. These tissue-specific melanosome geometries in pterosaurs indicate that manipulation of feather colour-and thus functions of feathers in visual communication-has deep evolutionary origins. These features show that genetic regulation of melanosome chemistry and shape(7-9) was active early in feather evolution. ; This work was funded by a Fonds National pour la Recherche Scientifique (F.R.S.-FNRS) FRIA grant (F3/5/5-MCF/ROI/BC-2319784), an Irish Research Council Government of Ireland Postdoctoral Fellowship (GOIPD/2018/768) awarded to A.C. and an ERC Starting Grant H2020-2014-StG-637691-ANICOLEVO and an ERC Consolidator Grant H2020-2020-CoG-101003293-PALAEOCHEM awarded to M.N. We thank M. Benton for providing the original data and code used in the phylogenetic reconstruction2, Z. Yang for providing raw melanosome measurements used to compare melanosome geometry in pterosaurs and J. Cillis for assistance with SEM. MCT.R.1884 was photographed by T. Hubin (RBINS).