The first discovery of in situ Pelophylax pueyoi (Amphibia: Anura) from the Late Miocene of Libros Konservat-Lagerstätte (Teruel, Spain)

ABSTRACT

For the first time, a specimen of Pelophylax pueyoi Navás, 1922a has been recovered in situ, about 600 meters from the main entrance inside the Libros II mine (Teruel, Spain). The fossil comes from the Libros Gypsum Unit (Late Miocene), and represents a nearly complete articulated adult frog exposed in ventral view, with partial preservation of soft tissues. The only apomorphic character diagnosing the family Ranidae is the presence of cylindrical sacral diapophyses. Other characteristics congruent with that of the family Ranidae can be observed: sphenethmoid fused medially, large and oval orbital fossa, well-developed pterygoids without alar expansion and the inner ramus clearly shorter than the posterolateral ramus, transverse processes of presacral vertebrae and sacral diapophyses of subequal length, sacrum unfused with the urostyle, probable bicondylar sacro-urostylar articulation, transverse processes of the urostyle lacking, absence of ribs, and elongated hind limb. An apomorphic combination of features of the genus Pelophylax can also be recognized, such as the more open sacral diapophysis, and less elongated and more robust femora than usually observed in the genus Rana. Finally, some discrete characteristics permit establishing a close relationship with P. pueyoi, such as the large size of the fossil, the wide proportion of the skull, and the somewhat trapezoidal distal contour of the V4 transverse processes. The carpus of P. pueyoi is described here for the first time, suggesting a similar condition of the adult carpal morphology found in most Neobatrachian species. Presence or absence of a praepollex in P. pueyoi still cannot be resolved.

ACKNOWLEDGMENTS

The authors would like to express their gratitude to the “Centro de Estudios espeleológicos turolenses,” who found the fossil frog, informed JIC and helped with the difficult excavation in the abandoned mine of Libros II. We also thank E. Diaz Berenguer (curator of the “Museo de Ciencias Naturales de la Universidad de Zaragoza”) for the loan of the material in her care, and to M. D. Guillén Espínola (IPHES) for the pictures of the fossils. Three reviewers A. Henrici (Carnegie Museum Of Natural History, Pittsburg, U.S.A.), R. Orencio Gómez (University of Buenos Aires, Argentina) and an anonymous reviewer, and the editors A. Huttenlocker and J. Harris provide useful comments on the former version of this manuscript. This research was funded by project GAČR 21-33751S of the Czech Science Foundation, and project 2017 SGR-859 from the Government of Catalonia (AGAUR). HAB is funded by project PID2021-122533NB-I00 from the Spanish Ministry of Science and Innovation. TP is supported by the Institute of Geology of the Czech Academy of Sciences (RVO67985831). JIC is funded by the Spanish Ministry of Science and Innovation (project PID2021-122612OB-I00) and by the Government of Aragón-FEDER 2014–2020 Construyendo Europa desde Aragón (Group E18: Aragosaurus: Recursos Geológicos y Paleoambientales). The research technical support of EMR and M. D. Guillén Espínola was supported by the Spanish Ministry of Science and Innovation through the “María de Maeztu” excellence accreditation (CEX2019-000945-M).