Tortugas europeas en el Congreso Internacional del Paleógeno celebrado en Bruselas

La semana pasada se ha celebrado en Bruselas el congreso internacional sobre la evolución y los paleoambientes en los que habitaron los primeros vertebrados modernos durante el Paleógeno (“International symposium Evolution and Paleoenvironment of Early Modern Vertebrates during the Paleogene”). Dado que desde el Grupo de Biología Evolutiva de la UNED se trabaja habitualmente con las faunas de reptiles de ese periodo, se han realizado algunas contribuciones a este congreso. En concreto, se han presentado los resultados relativos al análisis de dos linajes distintos de tortugas.

Por una parte, se ha defendido un trabajo preliminar sobre una tortuga primitiva, que podría representar una nueva forma. La importancia de este animal radica en que podría corresponder a la única tortuga primitiva hasta ahora registrada en niveles posteriores al Mesozoico para todo el Hemisferio Norte. El resumen de este trabajo es el siguiente:

Two lineages of basal turtles (i.e. members of Testudinata not attributable to the crown group Testudines) are identified in the Cretaceous record of Europe. One of them is known from the uppermost Jurassic to the uppermost Cretaceous. It is Helochelydridae, represented by several European species, but also known in the North American Cretaceous record. The other is represented by a single valid species, Kallokibotion bajazidi. This form is currently recognized as exclusive to the Maastrichtian (Late Cretaceous) record of the Hațeg Basin, in Transylvania (Romania). The basal turtles are very scarce in the Cenozoic record and, until now, they have not been described in the Northern Hemisphere. Although the survival of Kallokibotion beyond the Cretaceous was proposed from the preliminary observation of scarce material from the Paleocene area of Berru, in France, this hypothesis had not been demonstrated, having been subsequently considered as doubtful. The detailed study of this Paleocene turtle from Western Europe is presented here. Abundant material is identified, allowing its detailed characterization. Its attribution to a basal turtle (Stem Testudines) is confirmed. However, it is not referred to Kallokibotion, but it represents a still undiagnosed taxon.

Por otra parte, se han analizado algunos ejemplares de “tortugas de caparazón blando” (trioníquidos) gigantes del Paleógeno de Europa, incluyendo tanto la revisión de especímenes clásicos, hasta ahora pobremente conocidos, como el estudio de otros inéditos. El resumen de este trabajo es:

Remains of trionychid turtles are abundant in the early Eocene fossil record of Belgium. Several species are recognized there. In this context, the remains of several large-bodied individuals, with a shell length of about one meter, stand out both for their size and good preservation. The Royal Belgian Institute of Natural Sciences houses several unpublished large-size specimens, but also others with a high historical value (e.g., those from Erquelinnes and Leval), but which had not been, until now, studied in detail. Recent studies proposed that all large trionychids from the Eocene of Western Europe could belong to a single species, attributable to the North American genus Axestemys. However, a valid diagnosis for this putative European single species is not currently available, since the characters that allow its differentiation with each of the North American species have not been well established. Several of the best preserved Belgian specimens have been recently restored, which allows us to perform their detailed study. Thus, the description of several anatomical elements hitherto poorly known or not described for the large-bodied trionychids of the Eocene of Europe can be performed for the first time. The study of the Belgian specimens, which correspond to the most complete and best preserved in Europe, allows us to evaluate the hypothesis on whether they belong to the same species as the other large-bodied trionychids found in the Paleogene record of this continent. Thus, this study significantly increases the information on the relatively poorly known Paleogene large trionychids of Europe.

Referencias:

• Pérez-García, A. 2019. An enigmatic basal turtle (Stem Testudines) in the Paleogene of Europe. Abstract book of the International Symposium PalEurAfrica Evolution and Paleoenvironment of Early Modern Vertebrates during the Paleogene: 34.
• Pérez-García, A., Smith, T. 2019. The large trionychid turtles from the early Eocene record of Belgium. Abstract book of the International Symposium PalEurAfrica Evolution and Paleoenvironment of Early Modern Vertebrates during the Paleogene: 35.