Page:Countershading and Stripes in the Theropod Dinosaur Sinosauropteryx Reveal Heterogeneous Habitats in the Early Cretaceous Jehol Biota.pdf/7

 made about certain taxa inhabiting more- or less-densely forested areas [11], and owing to the volcanic nature of the deposits it is likely that a mosaic of habitats existed in the region, with open areas occurring among denser forested regions [32]. The paleobotanical record of Jehol shows plants adapted for both arid and humid environments, suggesting climatic fluctuations through time [12]. Because all paleobotanical remains are allocthonous with no in situ plant fossils known, it is likely that different plant communities existed in the regions around the Jehol lakes and further afield [12].

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. 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.

Further insight may come from the lizard in the stomach of NIGP 127587 (Figures 1D and 1E and S2). Of the known Jehol lizard fauna, the preserved skeletal elements most closely match those of Dalinghosaurus, found in the same deposits as Sinosauropteryx (the Yixian Formation) [33, 34]. The tail and hind limbs of Dalinghosaurus are exceptionally long relative to its forelimbs, which in modern lizards is a typical morphology of fast-moving terrestrial runners, potentially capable of bipedal locomotion at high speed [34, 35]. Shorter limbs are generally associated with arboreality [35]. Although the slender ungual phalanges of Dalinghosaurus indicate that it was likely capable of climbing [33], it appears likely it was better suited to living in the same open habitats inferred herein for the theropod.

Most groups of terrestrial vertebrates in Jehol show a strong tendency toward forest-living adaptations [11]. Sinosauropteryx, however, appears to be an exception to this rule. The insight that small theropods like Sinosauropteryx may have inhabited open habitats helps build a clearer picture of the environment in which the Jehol animals lived. Jehol clearly was not only rich taxonomically, but was also likely varied in the habitats available to animals and consisted of a mosaic of environments, which may explain the area’s extraordinary biodiversity [32]. Furthermore, the Jehol biota straddles more than 10 million years and is likely to have fluctuated in vegetation cover and landscape. Arboreal taxa and dinosaurs adapted in their color patterning to closed habitats were present in the forested areas [3, 9, 11] while larger dinosaurs and their smaller cryptically patterned prey explored open areas with less-dense vegetation. The presence of dinosaurs showing camouflage patterns adapted to different habitats indicates that the environment around the Jehol lakes was therefore diverse and varied and hosted different dinosaurian faunas. We have shown how a greater understanding of ancient environments can come from better understanding of the paleoecology of extinct animals through paleocolor reconstructions. This work furthers our understanding of how color patterns have evolved through time and highlights the importance of anti-predator camouflage strategies in deep time.

STAR&#9733;METHODS

Detailed methods are provided in the online version of this paper and include the following:


 * KEY RESOURCES TABLE
 * CONTACT FOR REAGENT AND RESOURCE SHARING
 * METHOD DETAILS
 * Institutional Abbreviations
 * Specimen Imaging
 * 2D Illustrations and Plumage Distribution
 * 3D Abdominal Modeling
 * Predicting Lighting Environment
 * QUANTIFICATION AND STATISTICAL ANALYSIS
 * Quantification of Countershading Transition
 * DATA AND SOFTWARE AVAILABILITY

SUPPLEMENTAL INFORMATION

Supplemental Information includes two figures and Supplemental Descriptions and can be found with this article online at https://doi.org/10.1016/j.cub.2017.09.032.

A video abstract is available at https://doi.org/10.1016/j.cub.2017.09.032#mmc3.

AUTHOR CONTRIBUTIONS

F.M.S. produced all illustrations and the reconstruction in Figure 2A, created and imaged the 3D models, and wrote the manuscript. J.V. devised the project concepts and imaged the fossils. R.N. produced the full art reconstruction in Figure 2B. I.C.C. produced the MATLAB models and performed the statistical analyses of countershading predictions versus the reconstruction. All authors commented on the manuscript.

ACKNOWLEDGMENTS

We would like to thank Yunbai Zhang and Diying Huang for access and help with specimens. We also thank Nick Longrich for discussion. F.M.S. was funded by the Natural Environment Research Council (PhD grant NE/L002434/1).

Received: May 18, 2017 Revised: August 14, 2017 Accepted: September 14, 2017 Published: October 26, 2017

REFERENCES

 Allen, W.L., Baddeley, R., Cuthill, I.C., and Scott-Samuel, N.E. (2012). A quantitative test of the predicted relationship between countershading and lighting environment. Am. Nat. 180, 762–776. Thayer, A.H. (1896). The law which underlies protective coloration. Auk 13, 124–129. Vinther, J., Nicholls, R., Lautenschlager, S., Pittman, M., Kaye, T.G., Rayfield, E., Mayr, G., and Cuthill, I.C. (2016). 3D camouflage in an ornithischian dinosaur. Curr. Biol. 26, 2456–2462. Rowland, H.M. (2009). From Abbott Thayer to the present day: what have we learned about the function of countershading? Philos. Trans. R. Soc. Lond. B Biol. Sci. 364, 519–527. 3342