Abstract
Preserved skin of small dinosaurs is rare. Here, a specimen of the ceratopsian dinosaur, Psittacosaurus, presents some of the best preserved epidermal scales observed to date in a relatively small dinosaur, over wide areas extending from the head to the tail. We study the preserved epidermis of SMF R 4970, the different types of scales, color, and patterns, and their respective locations in the body. We use modern application of high-power digital imaging for close-up analysis of the tubercles and fragments of preserved color. Three types of scales are preserved, large plate-like scales, smaller polygonal scales or tubercles, and round pebble-like scales. The sizes of the plate-like scales vary in different parts of the body and vanish altogether posteriorly. Light and dark cryptic patterns are created by the associations of the tubercle and plate-like scales, and there is also evidence of countershading in the proximal caudal region, the body darker dorsally and lighter ventrally. Perhaps most impressive are the distinctive pigmented impressions of scales over most of the skeletal elements. The pigmentation follows the curvature of the bones implying that when it was deposited, the skin was still pliable and able to wrap around the visible parts of the elements. The present record of color is the first in a non-theropod dinosaur and only the second record in a non-avian dinosaur. Because of its resistance to degradation and ability to produce various color tones from yellows to blacks, we suggest that melanin was the dominant chemical involved in the coloration of Psittacosaurus. The data here enable us to reconstruct the colors of Psittacosaurus as predominantly black and amber/brown, in cryptic patterns, somewhat dull, but useful to a prey animal. Indeed, skin pigment within a partially degraded bone indicates that Psittacosaurus was scavenged shortly after death. The theropod dinosaur Sinosauropteryx has recently been reported to have naturally pigmented integumental structures, which the authors interpret as proof that they are protofeathers and not support fibers of collagen. Our findings in Psittacosaurus, on the other hand, indicate a more parsimonious and less profound alternative explanation, i.e., decomposition of the skin releases pigments that readily permeate underlying structures.
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Acknowledgements
We express our gratitude to Sven Tränkner (Photographer) for the excellent digital images and Olaf Vogel (Preparator) for his skillful work and advice on the preparation of Psittacosaurus SMF R 4970 (both Geology Department, Senckenberg Museum). TLS thanks Kevin McGraw (Arizona State University) for discussions concerning color in vertebrates. We thank three reviewers for their extensive positive advice and encouragement which has benefited the paper substantially.
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GP—detailed examination of SMF R 4970 with respect to the material’s geology, lithology, preparation, and photography. TL-S—detailed analysis of the integument of Psittacosaurus SMF R 4970 based on digitized images of microstructures, zoological, paleontological and taphonomic interpretations, and writing the paper. This is an equal joint publication.
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ESM S1
Psittacosaurus SMF R 4970. High-resolution image of text-figure 2d. Dark plate-like scales surrounded by rings of amber/brown tubercles (white arrows) preserved over bone (proximal part of right scapula—see Fig. 1, circle); the amber/brown hue of the tubercles contrasts with the gray of the bone. Scale bar = 5 mm (GIF 476 kb)
ESM S2
Psittacosaurus SMF R 4970. High-resolution image of text-figure 3e showing the complete left coracoid and well-defined pigment impressions of tubercles (light and dark brown/black), overlying the upper part. Scale bar = 10 mm (GIF 388 kb)
ESM S3
A decomposing juvenile dolphin exhumed after several months burial. The most widespread and brightest pigment preservation overlies bone (white arrows), despite the thick underlying blubber or perhaps aided by it. The pigment is either absent (black arrowheads) or dull when preserved over the soft tissue (white arrowhead) or matrix (JPEG 268 kb)
ESM S4
The scaly skin of a hadrosaur showing worn surfaces of the scales (above) that may obscure fine surface texture and (below) that of Heloderma (gila monster ) showing a pappilose surface (after Matthew 1915) (JPEG 101 kb)
ESM S5
Psittacosaurus SMF R 4970. Right humerus, partial radius, and scapula. The tubercle impressions appear closely “wrapped” around the visible parts of the elements strongly indicative of the plasticity of the skin when this occurred (i.e. before mineralization). Note the stress fractures that subsequently occurred (GIF 771 kb)
ESM S6
Psittacosaurus SMF R 4970. A torn fragment of skin dislodged from adjacent to the vertebrae (top, large arrow) and displaced over the distal tips of the ischium, creasing at this point (indicated by the tubercles becoming sharply attenuated, arrowheads), and pubis. The three-pronged arrow shows rare detail of the torn fibers of a basal meshwork, which hold the scales in place and facilitate their movement (GIF 541 kb)
ESM S7
Psittacosaurus SMF R 4970. Distal part of right radius. A serendipidous fracture shows traces of pigmented scale impressions (arrows) from the torn skin on inner layers of the bone (arrowheads show stains on external surface), during decomposition of the skin. Color leaching from the epidermis to impregnate inner layers of bone could only have occurred shortly after fracture of the bone (i.e., evidence that the fracture was not post fossilization). However, within this fractured area we see a stress crack (detail, curved arrow) cutting across the scale imprint, suggesting that this crack occurred after the tubercle/pigment had become imprinted, possibly during compression. Large arrow shows direction bone was stripped-deepest to shallowest (indicated by numbers 1–4, respectively). The fractured radius gives a clue to circumstances surrounding the animal’s death—it was probably being scavenged at this point (see text). Curved double-headed arrows show possible bite impressions. Scale bar = 2 cm (GIF 293 kb)
ESM S8
George, a fleet-footed breed of hunting dog, Africanus (related to and about the size of a greyhound), descended from the court of the Egyptian pharaohs, shows counter shading, i.e., darker dorsal and lighter ventral parts of the body, including the tail, but lightening in an antero-posterior direction in the hind legs. George also demonstrates well cryptic markings that break up the body color (owned by Mrs Anne Knott—photo, Theagarten Lingham-Soliar) (JPEG 272 kb)
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Lingham-Soliar, T., Plodowski, G. The integument of Psittacosaurus from Liaoning Province, China: taphonomy, epidermal patterns and color of a ceratopsian dinosaur. Naturwissenschaften 97, 479–486 (2010). https://doi.org/10.1007/s00114-010-0661-3
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DOI: https://doi.org/10.1007/s00114-010-0661-3