Análisis del oído interno en tortugas botremídidas en las X Jornadas Internacionales de Salas de los Infantes

Durante las X Jornadas Internacionales sobre Paleontología de Dinosaurios y su Entorno, celebradas en Salas de los Infantes, se presentó en formato de póster un estudio de los oídos internos en los diferentes linajes de tortugas botremídidas. Este análisis se realizó a partir de las reconstrucciones tridimensionales de estas estructuras obtenidas a partir de la utilización de escáneres de CT. El estudio incluye varios taxones de botremídidos los cuales se han identificado como formas adaptadas a medios dulceacuícolas o marinos tanto litorales como pelágicos. En este estudio se realiza además la comparación con otras pleurodiras en las que se ha descrito el oído interno identificando algunas diferencias en la morfología de los canales semicirculares. El resumen de esta comunicación se expone a continuación:

Bothremydidae was a successful lineage of turtles within the Crown-group Pleurodira. Their representatives were widely distributed on most continents of both northern and southern hemispheres, and they were recognized from the Albian (Early Cretaceous) to the Eocene at least. All extant species of Pleurodira live in freshwater environments. However, the bothremydids occupied a wide range of aquatic habitats, not being limited to continental environments. Thus, the representatives of Cearachelyini and most members of Bothremydini were identified as freshwater turtles, while the representatives of Taphrosphyini and Nigeremydini, and also some species of Bothremydini (as the Maastrichtian Zolhafah bella), were recognized as marine forms. The proposed lifestyle for most bothremydid taxa is generally based on the interpretation of the sedimentary environments in which they were found. However, some anatomical modifications were identified as marine adaptations convergent with those observed in extant cryptodiran sea turtles, as the high-domed skulls or the elongated limb bones. The scarce neuroanatomical information available for Bothremydidae has not allowed to quantify modifications of the cranial cavities related to a particular lifestyle. Nevertheless, modifications in the endosseous labyrinth in response to adaptations for life in marine environments have been observed for different groups of reptiles. Thus, some groups of sauropterygians highly adapted to pelagic marine environments, such as plesiosaurs and sea cryptodiran turtles, have labyrinths with relatively short and wide semicircular canals. In contrast, Triassic sauropterygians adapted to coastal areas and marine crocodiles have relatively more elongated and narrow canals.

In this work, the inner ear of different lineages of bothremydid turtles were analyzed with the aim of identifying differences in this element related to adaptations to life in diverse aquatic environments. As in previous works on neuroanatomy of turtles, the analysis of the endosseous labyrinths of the bothremydids studied here was carried out using three-dimensional reconstructions generated from high-resolution CT-scan images. These virtual models have also been compared with those of other forms of turtles (both extant and extinct pleurodires and cryptodires) to identify modifications due to adaptation to different habitats. Relative measurements of the height and length of the semicircular canals have been used to identify these differences.

Although neuroanatomical studies are still relatively scarce for Bothremydidae, they provide valuable information on the modifications in the inner ears of this lineage. Although, in general terms, some previous studies have not revealed a direct relationship between the morphology of the inner ear and the lifestyle of the turtles, the endosseous labyrinths within Bothremydidae exhibit morphological differences across the lineages within this group. Bothremydid taxa identified as freshwater forms (i.e., Cearachelyini and most of Bothremydini) showed relatively elongated and narrow semicircular canals with a ratio between the length and the height above 2.20. However, the ratios measured for other taxa (i.e., the Bothremydini Zolhafah bella, Taphrosphyini, and Nigeremydini) are below 2.00, reflecting relatively anteroposteriorly shorter and dorsoventrally higher semicircular canals in the endosseous labyrinth. Comparison with both freshwater and marine turtle forms (both pleurodires and cryptodires) allows to identify morphological differences in the inner ears of bothremydids. This analysis provides new neuroanatomical evidence that confirms the previously proposed lifestyles for the different lineages within Bothremydidae.

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Más información:

Referencia: Martín-Jiménez, M., Pérez-García, A. 2025. Analysis of the morphological variability of the inner ear in the extinct bothremydid turtles. In P. Huerta, F. Torcida, J.I. Canudo and X. Pereda (eds.). Abstract Book/Libro de resúmenes X Jornadas Internacionales sobre Paleontología de Dinosaurios y su entorno, 151-152.

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