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.
The authors declare no competing financial interests.
Extended data figures and tables
Extended Data Figure 9 Melanosome diameters and aspect ratios observed in extant feathers, lepidosaur, testudine and archosaur skin, and mammalian hair.
Melanosome diameters are shown in a, and aspect ratios are shown in b. Boxplot colours correspond with integument colour: black, brown, grey. For feathers, ‘penguin-like’ is shown in blue and iridescent is shown in purple. Lines are median values, boxes are quartiles, lines are range. Boxplots sharing the same letter (v, w, x, y, z) are not significantly different from one another.
Extended Data Figure 10 Exploration of the potential effects of taphonomy and sampling on the observed differences in melanosomes in skin, hair, filaments and feathers.
Top, melanosome diversity is adjusted to model taphonomic shrinkage of melanosomes suggested from experimental studies. Values for all fossil samples were adjusted (enlarged by 20%) based on the findings of ref. 18 (Supplementary Methods). Original data points are shown in colours and adjusted data are shown in grey. Grey regions indicate the extent of the total melanosome morphospace from the primary analyses. The pattern reported (i.e., increased diversity and higher-aspect-ratio forms only in Maniraptora and Mammalia) is not affected (Fig. 4, main text; n for each integumentary type is identical to the primary analysis). Bottom, to consider the effect of sampling on the observed pattern samples from near the thoracic region were removed from the database. Although there was no evidence to suggest that these samples were from internal organs, or that such organs were preserved, because melanosomes are present in some internal organs in extant taxa, the sensitivity of the results to removal these samples was explored. There was no effect on the pattern reported from the primary analysis (compare Fig. 4). Samples 1 and 2 from Yabeinosaurus sp. (PKUP V1059), sample 1 from Psittacosaurus lujiatunensis (PKUP V1050), samples 121, 122 and 123 from Caudipteryx zoui (PMOL AD00020), samples 11, 13 and 14 from an undescribed enantiornithine (CUGB P1201), samples 30 and 33 from an undescribed enantiornithine (CUGB G20120001), and samples 64–69, 89 and 90 from an undescribed ornithurine bird (CUGB G20100053) were removed from the database. Samples are colour coded as in Fig. 4, main text and adjusted n for subsampling analysis follows: extant mammal hair (blue, n = 719), skin from extant (dark green, n = 742) and extinct (light green, n = 605) lepidosaurian, testudine and archosaurian species, feathers in basal Paraves (yellow, n = 1,212), Confuciusornis and crown-ward extinct avialan taxa (orange, n = 1,376), extant Aves (bright red, n = 3,294) and flightless palaeognath birds (dark red, n = 107). Colours of silhouettes correspond with colours in scatterplots. Black indicated unsampled taxa or integumentary type (e.g., bristle structures on the tail of Psittacosaurus).
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Li, Q., Clarke, J., Gao, KQ. et al. Melanosome evolution indicates a key physiological shift within feathered dinosaurs. Nature 507, 350–353 (2014). https://doi.org/10.1038/nature12973
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