A fossil sea turtle (Reptilia, Pan-Cheloniidae) with preserved soft tissues from the Eocene Fur Formation of Denmark

ABSTRACT

A new hard-shelled sea turtle (Pan-Cheloniidae) with vestigial soft tissues from the lower Eocene (Ypresian) Fur Formation of Denmark is described and illustrated. The fossil (DK 807) comprises a partial, yet fully articulated carapace (estimated original length ∼50  cm) where the individual bones mostly are preserved in three dimensions, together with an intact sacrum, a consecutive series of articulated caudal vertebrae, a complete pelvic girdle, and both hind limbs. Primitive characters in the pelvis and limbs, along with free ribs that contact the posterior peripherals suggest affinity with the extinct pan-cheloniid Eochelone; however, because of the incomplete nature of the fossil, DK 807 is kept in open nomenclature. Associated with the skeletal elements are soft-tissue residues that include remnant epidermal scutes and a nearly complete outline of a rear paddle. The flipper-shaped halo likely represents traces of skin preserved as a dark bedding-parallel film. Its wrinkled and striated surface texture attests to an originally scaleless configuration comparable to the soft integument of living adult dermochelyid (leatherback) turtles, and unlike that of extant cheloniids. Scratches, scars and indentations on the bony carapace likely represent incompletely healed bite marks inflicted by a crocodylian or another large-sized seagoing tetrapod.

ACKNOWLEDGMENTS

We would like to thank F. Osbæck for taking pictures of DK 807 during the preparation of the fossil. We would also like to express our gratitude to D. Lawver for providing information on turtle anatomy, M. Mostadius for giving us access to testudines housed in the zoological collections at Lund Biological Museum, J.C. Sagebiel for access to pan-cheloniids in the collections at the University of Texas at Austin’s Vertebrate Paleontology Laboratory, B.E.K. Lindow for information on the Danish pan-cheloniid collection at NHMD, B.P. Schultz and R.L. Sylvestersen for access to the fossil turtle material at FUM, and last but not least, A. Folie and C. Cousin for access to the pan-cheloniid collection at IRSNB. We are also grateful for the assistance from G. Bianco at the 3D Laboratory, Department of Biology, Lund University. The authors are thankful to editor T. Lyson for the handling of the manuscript, and reviewers E. Cadena, E. Vlachos, and S. Evers for their constructive comments that greatly improved the quality of this paper. Financial support was provided through a Grant for Distinguished Young Researchers to J.L. (Swedish Research Council, award No. 642-2014-3773).