Neuroanatomical Study and Three-Dimensional Reconstruction of the Skull of a Bothremydid Turtle (Pleurodira) Based on the European Eocene Tartaruscola teodorii

Abstract

Bothremydidae is a successful lineage of pleurodiran turtles that lived from the Cretaceous to the Paleogene, and are found in most continents of both Laurasia and Gondwana. Despite numerous known cranial remains of this clade, no study on the complete neuroanatomical reconstruction of any of its representatives has been published so far. Tartaruscola teodorii is a French lower Eocene member of Foxemydina (Bothremydini), known by two skulls. It is one of the few bothremydids identified in the Cenozoic record of Europe. The present study includes the complete three-dimensional reconstruction of each of the cranial bones of both the holotype and the paratype of T. teodorii, increasing the anatomical information about this species. The virtual reconstruction of its neuroanatomical structures is presented here, including the cranial cavity, nerves, nasal cavity, inner ears, and carotid arteries. This analysis is the first detailed neuroanatomical study performed for a member of Bothremydidae. In addition, the virtual reconstruction of the neuroanatomical structures of some extant taxa belonging to several pleurodiran lineages (Chelidae, Pelomedusidae and Podocnemididae), are also carried out and analyzed, so that the comparative framework for Pleurodira is remarkably improved.

The neuroanatomy of the bothremydid pleurodiran turtle Galianemys, from the Late Cretaceous (Cenomanian) of Morocco

“…The anterior semicircular canal is longer than the posterior canal in both species of Galianemys, but the ratio between those canals for Galianemys whitei (1.21 and 1.37 for the left and right inner ears, respectively) is higher than measured for Galianemys emringeri (1.16 and 1.21 for the left and right inner ears). The value of this ratio known for other bothremydid turtles (i.e., Tartaruscola teodorii [Martín-Jiménez & Pérez-García, 2021] [Grandidier, 1867]; see table 1 in Martín-Jiménez & Pérez-García, 2021), is relatively longer than in Bothremydini and Taphrosphyini. In addition, the anterior semicircular canal observed here for the right inner ear of both species of Galianemys is clearly higher than the posterior one, contrary to the condition in all known members of the lineages of Bothremydini (e.g., Araiochelys hirayamai, Bothremys maghrebiana, Bothremys cooki, and Bothremys kellyi) and Taphrosphyini (e.g., Taphrosphys ippolitoi, Labrostochelys galkini, Phosphatochelys tedfordi, and Ummulisani rutgerensis) identified by this character, in which the dorsal surfaces of these canals are at the same level (see supplementary file in Hermanson et al, 2020).…”

“…Finally, the figures were composed using Adobe Photoshop CS6. The neuroanatomical structures observed for both specimens of Galianemys were compared with those previously described for other bothremydids (see Martín‐Jiménez & Pérez‐García, 2021, and references therein).…”

“…In addition, each bone of the specimen MNHN.F MRS 2098 was individually reconstructed, and they were figured, in articulation, using a different color for each of them (Figures 5–7). The linear and angular measurements of the cavum cranii, carotid canals and of the labyrinths were obtained following the protocols previously established in the literature (see supplementary information in Hermanson et al, 2020 and supplementary file 2 in Martín‐Jiménez & Pérez‐García, 2021), but including new measurements as those of the cartilaginous ridge and the height of the cranial cavity. These data were obtained using the measure tools of Avizo 7.1.…”

“…Until now, partial reconstructions of some cranial regions have been performed for very few taxa of Bothremydidae, as is the case of the basicranial bones of the Taphrosphyini taxa Ummulisani rutgersensis Gaffney, Tong & Meylan, 2006 and Labrostochelys galkini Gaffney, Tong & Meylan, 2006, and also of the cranial roof of the Bothremydini taxon Bothremys kellyi Gaffney, Tong & Meylan, 2006 (see Hermanson et al, 2020). A 3D reconstruction of the skull of the Cearachelyini Galianemys whitei was carried out by Hermanson et al (2020), but the generation of a 3D model for each cranial bone was only done for the Bothremydini Tartaruscola teodorii Pérez‐García, 2016 within Bothremydidae (Martín‐Jiménez & Pérez‐García, 2021). In addition, the first complete neuroanatomical study from the 3D reconstructions of the internal cranial structures for Cearachelyini is carried out here.…”

“…The neuroanatomical structures of both specimens studied here are compared with previously described or figured for other bothremydid turtles, including the endocranial casts of the Bothremydini Bothremys cooki (Leidy, 1865) and Chedighaii barberi (Schmidt, 1940) (Gaffney & Zangerl, 1968); the natural endocast of Chedighaii sp. (Gaffney, 1977); the virtual 3D reconstruction of the inner ear of the Bothremydini Bothremys maghrebiana Gaffney, Tong & Meylan, 2006; the cranial cavity of the Taphrosphyini Phosphatochelys tedfordi Gaffney & Tong, 2003; the carotid circulation of the Cearachelyini Galianemys whitei , and the Taphrosphyini Ummulisani rutgersensis and Labrostochelys galkini ; the partial canalis cavernosus and some cranial nerves of the last two taxa (Hermanson et al, 2020); and the only relatively complete neuroanatomical reconstruction so far available for Bothremydidae (i.e., that of the Bothremydini Tartaruscola teodorii , Martín‐Jiménez & Pérez‐García, 2021).…”