The Fenestras Elisabeth Complex (Nova Structura) in the Parietal Bone of Plecotus auritus: Morphology, Topography, and Functional Significance

Fenestrations of mammalian skull bones are rare and poorly understood, particularly within the parietal bone. In bats-a group characterised by advanced sensory specialisation and echolocation-superficial modifications of the cranial vault may have functional significance, yet their occurrence and organisation remain insufficiently documented. In this study, we describe an exceptional fenestrated complex in the posterolateral parietal bone of <i>Plecotus auritus</i>, comprising structural elements not previously recorded within Vespertilionidae. The aim of the study was to characterise in detail the morphology, topography, and variability of the surface structure termed Fenestras Elisabeth (nova structura), with particular emphasis on its relationship with the auditory region and its potential biomechanical-acoustic significance. The material consisted of ten skulls of <i>P. auritus</i>, examined using micro-CT scanning, 3D reconstruction, and qualitative analysis of fenestrated structures and their topographic relationships. Within the posterolateral parietal region, we identified an extensive and repeatable fenestrated complex comprising numerous fenestrae parietales Elisabeth, paired fenestrula Elisabeth, a central depression (recessus acousticus parietalis), and a bordering fissure (fissura occipitalis mastoidea, nova structura topographica). The complex exhibited a stable spatial organisation despite individual variation in the number and shape of the openings. All fenestrations were confined to the posterolateral zone, and the contact between the fenestrae and the fissura occipitalis mastoidea represented a diagnostic feature. Our analysis suggests that the Fenestras Elisabeth complex may be associated with combined biomechanical and acoustic constraints: (1) a biomechanical role-reducing strain in the parietal lamina during movements of the extremely mobile and elongated pinnae; and (2) an acoustic role-modulating micro-vibrations transmitted to the inner-ear structures. Individual variability and lateral asymmetry of fenestration patterns indicate a high degree of adaptive plasticity in this region of the skull. This study provides the first documentation of a large, structurally organised parietal-bone fenestration complex in <i>Plecotus auritus</i>, expanding current knowledge of bat cranial morphology and suggesting a likely functional significance for these previously unknown bony structures.