Paleobiological forensic study of an upper Miocene Pelobates tadpole (Anura, Pelobatidae) from the Tresjuncos lagerstätte of central Spain

ABSTRACT

A paleobiological reconstruction of the last hours of life of an exceptionally well-preserved fossil tadpole is carried out through morphological and taphonomic analyses, allowing inferences to be made about its identification, developmental stage, physical condition, health, behavior, death, and burial. The tadpole was recovered from an upper Miocene (Turolian, MN13) diatomaceous konservat-lagerstätte deposit near Tresjuncos (Cuenca Province, Spain). The specimen belongs to an unnamed species of Pelobates (Pelobatidae) of the westernmost Palearctic phylogenetic clade. Its gigantic size was due neither to metabolic (hypothyroidism) nor to ecological (overwintering) causes but merely reflects an optimum living environment. Dying at Gosner developmental stage 41, the ossification pattern of the tadpole is slightly discordant with that of extant Pelobates cultripes, a greater degree for the skull and vertebral column in the fossil. The tadpole, seemingly in excellent health, had an intestine containing abundant remains of an epiphytic/epipelic diatom, different from the planktonic species surrounding the fossilized body. Death was probably violent, as revealed by a fossil hollow trace similar to hematomas made by egret beak strikes. Rapid burial coincided with an occurrence of massive planktonic diatom sedimentation distant from the lakeshore.

ACKNOWLEDGMENTS

We are grateful to the technical staff of the Museo Nacional de Ciencias Naturales (MNCN-CSIC, Madrid) laboratories, and in particular to L. Tormo, M. Furió, and A. Jorge (SEM, EDS), J. Muñoz (photography), and P. Valverde (3D microscopy). We also thank M. Calvo and A. Sánchez for their assistance with the MNCN-CSIC herpetological collection. M. Mañez, D. Buckley, and Í. Martínez-Solano shared their expertise on bird predation and tadpole behavior with us. M. Tejedo kindly provided information and photographs of tadpoles attacked by birds in outdoor experiments. We are grateful to A. D. Buscalioni, F. Ortega, J. L. Ortiz, and J. L. Sanz for recovery of the fossil tadpole and for entrusting it to us, and to M. Modrell and R. Márquez for linguistic corrections. We appreciate the help received from the reviewers of this article, in particular the detailed comments made by J. Gardner and Z. Roček. The present research was funded by the Spanish Project CGL2014-54818-P (Ministerio de Economía, Industria y Competitividad, FEDER, European Union).