An Upper Miocene marine turtle from Panama that preserves osteocytes with potential DNA

ABSTRACT

Lepidochelys is a genus of extant marine turtles that includes the critically endangered Kemp's Ridley turtle. The evolutionary history of this genus is poorly understood due to the lack of an undisputed fossil record for the group. Here we describe a partially preserved carapace from the Upper Miocene Chagres Formation of Panama, which represents the oldest fossil record of Lepidochelys. The specimen has rectangular, anteroposteriorly short pleural scutes, a characteristic shared with members of Lepidochelys. It is potentially closely related to L. olivacea because it shares a similar number of pleurals, but its precise taxonomic status remains uncertain. We discuss the ecological role that a marine turtle played in the paleoecosystem of the Chagres Formation. The new specimen exhibits exceptional preservation of bone sutures, sulci, sculpturing, and bone microstructure, including remains of blood vessels, collagen fibers, and osteocytes. This is the first time that a histochemical stain (DAPI) indicates preservation of a compound consistent with DNA in a fossil vertebrate outside Dinosauria. These data demonstrate the potential for DNA to persist in specimens that are both millions of years old and are from lower latitudes, which challenges traditional paradigms of biomolecular preservation.

ACKNOWLEDGMENTS

We thank S. Evers for sharing photos of some extant taxa. Thanks to curators of different institutions that allowed access to collections to examine specimens, including: Instituto de Ciencias Naturales, Universidad Nacional de Colombia (Bogotá, Colombia), Senckenberg Natural History Collections (Dresden, Germany), Muséum national d'histoire naturelle (Paris, France), Naturhistorisches Museum Wien (Vienna, Austria), Smithsonian National Museum of Natural History (Maryland, U.S.A.), and Museo de la Salle, Universidad de la Salle (Bogotá, Colombia). Thanks to F. Rodriguez and to A. Osorio for their help during the field excavations. Our thanks to the Dirección de Recursos Minerales of Panamá for field collection permits and to K. Cardenas and C. de León from Smithsonian Tropical Research Institute for helping us on transport permits to study the specimen. Two anonymous reviewers and editor T. Lyson made constructive suggestions for improvement of the manuscript. Thanks to R. Perez S.A. for the vehicles used during the field explorations. The study resulted in part from a project, which is funded to C. De Gracia by the program of young researchers (grant No. APY–N110–016A) and the Doctoral and Postdoctoral Scholarships Program of the National Secretary of Science and Technology of Panama (Grant No. BIP2018–004). Funding was granted to E-A. Cadena from Dirección de Investigaciones e Innovación (DIeI) Universidad del Rosario, Proyectos de Investigación, grant IV-FMD001, 2022.

AUTHOR CONTRIBUTIONS

E-AC and C.D-G designed the project. E-AC and D. A.C-R gathered, analyzed the data, and wrote the first draft of the manuscript. All authors edited the manuscript.

SUPPLEMENTARY FILES

Supplementary Data _1.docx: List of fossil and extant specimens of marine turtles directly examined.