Inference of colour patterning in extinct dinosaurs1,2,3 has been based on the relationship between the morphology of melanin-containing organelles (melanosomes) and colour in extant bird feathers. When this relationship evolved relative to the origin of feathers and other novel integumentary structures, such as hair and filamentous body covering in extinct archosaurs, has not been evaluated. Here we sample melanosomes from the integument of 181 extant amniote taxa and 13 lizard, turtle, dinosaur and pterosaur fossils from the Upper-Jurassic and Lower-Cretaceous of China. We find that in the lineage leading to birds, the observed increase in the diversity of melanosome morphologies appears abruptly, near the origin of pinnate feathers in maniraptoran dinosaurs. Similarly, mammals show an increased diversity of melanosome form compared to all ectothermic amniotes. In these two clades, mammals and maniraptoran dinosaurs including birds, melanosome form and colour are linked and colour reconstruction may be possible. By contrast, melanosomes in lizard, turtle and crocodilian skin, as well as the archosaurian filamentous body coverings (dinosaur ‘protofeathers’ and pterosaur ‘pycnofibres’), show a limited diversity of form that is uncorrelated with colour in extant taxa. These patterns may be explained by convergent changes in the key melanocortin system of mammals and birds, which is known to affect pleiotropically both melanin-based colouration and energetic processes such as metabolic rate in vertebrates4, and may therefore support a significant physiological shift in maniraptoran dinosaurs.
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This work was supported by the National Natural Science Foundation of China (NSFC) grant 41272031, Fundamental Research Funds for Central Universities, Beijing Municipal Bureau of Human Resources, NSF grants EAR-1251895 and 1251922, Human Frontier Science Program (HFSP) grant RGY-0083, Air Force Office of Scientific Research (AFOSR) grant FA9550-13-1-0222, and the Jurassic Foundation. The Smithsonian Institution (J. F. Jacobs and A. Wynn) and San Diego Museum of Natural History (P. Unitt) provided extant samples. BMNHC PH000911 was photographed by M. Ellison.
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This file contains Supplementary Methods, Supplementary Tables 1-3 and additional references.
About this article
Trends in Ecology & Evolution (2019)