Biochemistry and adaptive colouration of an exceptionally preserved juvenile fossil sea turtle
Johan Lindgren, Takeo Kuriyama, Henrik Madsen, Peter Sjövall, Wenxia Zheng, Per Uvdal, Anders Engdahl, Alison E. Moyer, Johan A. Gren, Naoki Kamezaki, Shintaro Ueno & Mary H. Schweitzer
Scientific Reports 7, Article number: 13324 (2017)
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Received: 17 May 2017 Accepted: 19 September 2017 Published online: 17 October 2017
Holotype of Tasbacka danica . (a) Photograph of the fossil. Fo , fontanelle (the light colour is a result of sediment infill); Hyo, hyoplastron ; Hyp, hypoplastron ; Ne, neural; Nu, nuchal ; Pe , peripheral; Py, pygal . Arrowheads indicate neural nodes. (b) Detail of the carapace with the sampled area demarcated by a circle. Co, costal; Hu, humerus; Sc, scapula. (c) Higher magnification image showing marginal scutes (arrowheads), pigmentations on bones (arrows), and a brown-black film covering the fontanelles (stars).
Abstract
The holotype (MHM-K2) of the Eocene cheloniine Tasbacka danica is arguably one of the best preserved juvenile fossil sea turtles on record. Notwithstanding compactional flattening, the specimen is virtually intact, comprising a fully articulated skeleton exposed in dorsal view. MHM-K2 also preserves, with great fidelity, soft tissue traces visible as a sharply delineated carbon film around the bones and marginal scutes along the edge of the carapace. Here we show that the extraordinary preservation of the type of T. danica goes beyond gross morphology to include ultrastructural details and labile molecular components of the once-living animal. Haemoglobin -derived compounds, eumelanic pigments and proteinaceous materials retaining the immunological characteristics of sauropsid -specific β-keratin and tropomyosin were detected in tissues containing remnant melanosomes and decayed keratin plates. The preserved organics represent condensed remains of the cornified epidermis and, likely also, deeper anatomical features, and provide direct chemical evidence that adaptive melanism – a biological means used by extant sea turtle hatchlings to elevate metabolic and growth rates – had evolved 54 million years ago.
Acknowledgements
Ola Gustafsson assisted during the TEM analyses. James Parham provided information on sea turtle anatomy, whereas Edwin Cadena provided samples of an extant analogue for controls. This research was supported through a Grant for Distinguished Young Researchers (award number 642-2014-3773; Swedish Research Council) to J.L. Part of this work was performed at the Analytical Instrumentation Facility at North Carolina State University, which is supported by the State of North Carolina and National Science Foundation (award number ECCS-1542015). Further support was provided through a National Science Foundation INSPIRE grant (award number EAR-1344198) to M.H.S. and W.Z., and the National Science Foundation Graduate Research Fellowship Program (award number DGE-1252376) to A.E.M.
Author information
Affiliations
Department of Geology, Lund University, 223 62, Lund, Sweden
Johan Lindgren, Takeo Kuriyama, Johan A. Gren & Mary H. Schweitzer
Institute of Natural and Environmental Sciences, University of Hyogo, 669 3842 , Hyogo, Japan
Takeo Kuriyama
Wildlife Management Research Center, 669 3842, Hyogo, Japan
Takeo Kuriyama
Henrik Madsen
RISE Research Institutes of Sweden, Chemistry and Materials, 501 15 , Borås, Sweden
Peter Sjövall
Department of Biological Sciences, North Carolina State University, Raleigh, NC, 27695, USA
Wenxia Zheng, Alison E. Moyer & Mary H. Schweitzer
North Carolina Museum of Natural Sciences, Raleigh, NC, 27601, USA
Wenxia Zheng & Mary H. Schweitzer
Chemical Physics, Department of Chemistry, Lund University, 221 00, Lund, Sweden
Per Uvdal
MAX-IV laboratory, Lund University, 221 00, Lund, Sweden
Anders Engdahl
Department of Biosphere-Geosphere Science, Okayama University of Science, 700 005, Okayama, Japan
Naoki Kamezaki
Department of Ecosystem Studies, University of Tokyo, 113 8657, Tokyo, Japan
Shintaro Ueno
Contributions
J.L. designed the research. J.L., M.H.S. and P.S. wrote the manuscript with input from all other authors. H.M. collected and prepared MHM-K2. T.K., J.L., P.S., and J.A.G. carried out the FEG-SEM and TEM analyses, M.H.S. and W.Z. performed the immunohistochemical investigation, P.S. and J.L. conducted the ToF-SIMS experiments, and P.U., A.E. and J.L. recorded the IR microspectroscopic measurements. A.E.M. developed the chicken feather antibodies used in this study, whereas N.K. and S.U. provided reference materials.
Competing Interests
The authors declare that they have no competing interests.
Corresponding author
Correspondence to Johan Lindgren.
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