Digital reconstruction of the inner ear of Protypotherium (Mammalia; Notoungulata)

BRENDA MARIEL AGUIAR; KAREN ULLOA-GUAQUIN; BARBARA VERA; ARIANA PAULINA CARABAJAL

Río Negro, General roca

Otro; Reunión de comunicaciones de la Asociación Paleontológica Argentina; 2024

Asociación Paleontológica Argentina

Notoungulata includes diverse native ungulates that played a vital role in South America´s Cenozoic ecosystems in terms of variety, form, and lifestyles. Among them, the Interatheriinae Protypotherium stands out as the most diverse and widely distributed Neogene genus. MAPBAR 8371 (curated in the Museo Paleontológico Bariloche) was assigned to Protypotherium sp. This specimen is a well-preserved skull from the Collón Curá Formation (Comallo, Río Negro Province, Argentina). It conserves most of the neurocranium, craniofacial region, and molariform series. We digitalized the skull using a Cone Beam Computed Tomograph (in Consultorios Albarracín, San Carlos de Bariloche) to explore the internal anatomy, especially the inner ear. The performed segmentation was made with the software Mimics (21.0). In the inner ear a segment of the semicircular canals, the vestibular region, and the cochlea, crucial elements for balance and hearing were identified. There are also anterior and posterior ampullae canals, as well as a section of the crus commune. In the vestibular region, specifically on its lateral-external face, the fenestra vestibuli and the fenestra cochleae were observed. The bulge, corresponding to the spherical recess containing the saccule, is conspicuous and positioned above the fenestra vestibuli. The morphology of the vestibule in this specimen, exhibiting significant dilation, is comparable to that described in Cochilius, an early Miocene Interatheriinae. In the right inner ear of MAPBAR 8371, the cochlear canal is fully preserved, with two complete turns counted. This is consistent with that of described in other notoungulates, such as Pachyrukhos, Cochilius, and Altitypotherium, while it, differs from Notostylops (2.25). These results suggest that the inner ear of Protypotherium shares both similarities and distinctions with other Typotheria members, particularly Cochilius and Notostylops. In order to provide more detailed descriptions, not only of the inner ear but also of the neuroanatomy and craniofacial soft tissues, the internal anatomy in these groups needs to be more extensively explored.