The inner morphology of the petrosal bone of the endemic elephant of Tilos Island, Greece

Abstract

The bony labyrinth, as part of the inner structure of the petrosal bone, contains the sensory organs of balance and hearing. The semicircular canals, as part of the vestibular apparatus of the inner ear, are involved in the detection of angular motion of the head for maintaining balance and guiding locomotor behavior. While the overall structure of the bony labyrinth is inaccessible embedded in the petrosal bone, high resolution computed tomography makes the study of these structures possible. The purpose of this study is to visualize and precisely quantify the complex inner ear structures of the insular mammal Palaeoloxodon tiliensis and comment on the relationship of these morphologies to the agility and hearing frequency ranges. This study focuses on imaging the shape of the bony labyrinth as well as the semicircular canals, of three petrosal bones, using micro-computed tomography (micro-CT). Shape and size analysis of the cochlea allow for an assessment of morphological differences between species. Specifically, measuring the dimensions of inner ear components as well as the angular distances can express the variation in their balancing abilities and the frequencies of their auditory perception. The morphological characteristics obtained through micro-CT lead to the conclusion that P. tiliensis retained similar conditions to that of its larger relatives, and it was an animal that had hearing in the low frequency ranges. Dionysia E. Liakopoulou. National and Kapodistrian University of Athens, Faculty of Geology and Geoenvironment, Panepistimiopolis, 15784 Athens, Greece, dliakopoulou@geol.uoa.gr George E. Theodorou. National and Kapodistrian University of Athens, Faculty of Geology and Geoenvironment, Panepistimiopolis, 15784 Athens, Greece, gtheodor@geol.uoa.gr Anneke H. van Heteren. Zoologische Staatssammlung München – Staatliche Naturwissenschaftliche Sammlungen Bayerns, Münchhausenstraße 21, 81247 München, Germany; Ludwig-MaximiliansUniversität München, GeoBio-Center, Richard-Wagner-Straße 10, 80333 Munich, Germany; LudwigMaximilians-Universität München, Department Biologie II, Großhaderner Straße 2, 82152 PlaneggMartinsried, Germany, vanHeteren@snsb.de LIAKOPOULOU, THEODOROU, & VAN HETEREN: PETROSAL BONE MORPHOLOGY 2