Fiann M. Smithwick, Robert Nicholls , Innes C. Cuthill, and Jakob Vinther

“ This allows the determination of likely habitats of animals based on quantification of color patterns [1, 3] . Those that inhabit open environments with direct lighting conditions generally exhibit a sharp transition from dark to light color high up on the flanks of the body [1, 3] . Conversely, animals inhabiting a more closed habitat with diffuse lighting coming in at many angles often show a smoother gradation from dark to light lower down on the body [1, 3] . ”

“ Reconstructed patterns match well with those predicted for animals living in open habitats. Jehol is presumed to have been a predominantly closed forested environment [3, 11, 12] , but our results indicate a more heterogeneous range of habitats. Sinosauropteryx is also shown to exhibit a "bandit mask," a common pattern in many living vertebrates, particularly birds, that serves multiple functions including camouflage [13–18] . Sinosauropteryx therefore shows multiple color pattern features likely related to the habitat in which it lived. ”

“ It has been proposed that the larger theropods of Jehol would likely have been found in more open areas, where vegetation was less likely to impede their movement [11] . The countershading pattern of Sinosauropteryx indicates that it, too, inhabited these more open areas where predation pressure may have been significantly higher due to reduced cover than in the closed areas and where background-matching camouflage was more difficult to achieve. A need to reduce conspicuousness relative to the environment would therefore have been important to avoid detection from keen visual predators. ”

“ Applying these principles, we describe the pattern of countershading in the diminutive theropod dinosaur Sinosauropteryx from the Early Cretaceous Jehol Biota of Liaoning, China. From reconstructions based on exceptional fossils, the color pattern is compared to predicted optimal countershading transitions based on 3D reconstructions of the animal’s abdomen, imaged in different lighting environments. ”

“ The consistency of plumage patterns observed across multiple specimens gives confidence to the reconstructed color pattern. The pattern of pigment across the face appears to show a band of pigmented plumage running from the dorsal area of the head anterioventrally, which then angles toward the eye before running to the posterioventral margin of the lower jaw (Figures 3A–3E) . The banded tail shows a transition from narrow to widely spaced bands from the proximal to distal regions, with the ventral pigmentation becoming denser toward the end of the tail. ”

“ The diminutive size of Sinosauropteryx and its relatively high countershading transition adapted for open areas indicates that it lived in habitats with either few plants or very low vegetation cover. ”