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Two early Late Pleistocene (~105,000- to 125,000-year-old) crania from Lingjing, Xuchang, China, exhibit a morphological mosaic with differences from and similarities to their western contemporaries. They share pan–Old World trends in encephalization and in supraorbital, neurocranial vault, and nuchal gracilization. They reflect eastern Eurasian ancestry in having low, sagittally flat, and inferiorly broad neurocrania. They share occipital (suprainiac and nuchal torus) and temporal labyrinthine (semicircular canal) morphology with the Neandertals. This morphological combination reflects Pleistocene human evolutionary patterns in general biology, as well as both regional continuity and interregional population dynamics.

Jawed vertebrates have inner ears with three semicircular canals, the presence of which has been used as a key to understanding evolutionary relationships. Ostracoderms, the jawless stem gnathostomes, had only two canals and lacked the lateral canal 1 – 3 . Lampreys, which are modern cyclostomes, are generally thought to possess two semicircular canals whereas the hagfishes—which are also cyclostomes—have only a single canal, which used to be regarded as a more primitive trait 1 , 4 . However, recent molecular and developmental analyses have strongly supported the monophyly of cyclostomes 5 – 7 , which has left the evolutionary trajectory of the vertebrate inner ear unclear 8 . Here we show the differentiation of the otic vesicle of the lamprey Lethenteron camtschaticum and inshore hagfish Eptatretus burgeri . This is the first time, to our knowledge, that the development of the hagfish inner ear is reported. We found that canal development in the lamprey starts with two depressions—which is reminiscent of the early developmental pattern of the inner ear in modern gnathostomes. These cyclostome otic vesicles show a pattern of expression of regulatory genes, including OTX genes, that is comparable to that of gnathosomes. Although two depressions appear in the lamprey vesicle, they subsequently fuse to form a single canal that is similar to that of hagfishes. Complete separation of the depressions results in anterior and posterior canals in gnathostomes. The single depression of the vesicle in hagfishes thus appears to be a secondarily derived trait. Furthermore, the lateral canal in crown gnathostomes was acquired secondarily—not by de novo acquisition of an OTX expression domain, but by the evolution of a developmental program downstream of the OTX genes. The differentiation of the inner ear in the lamprey Lethenteron camtschaticum and hagfish Eptatretus burgeri sheds light on the evolution of the semicircular canals of jawed vertebrates.

Revealing the evolutionary processes which resulted in the derived morphologies that characterize the Neanderthal clade has been an important task for paleoanthropologists. One critical method to quantify evolutionary changes in the morphology of hominin populations is through evaluating morphological phenotypic diversity (i.e., disparity) in phylogenetically informative bones as a close proxy to neutral evolutionary processes. The goal of this study is to quantify the degree of disparity in the Neanderthal clade. We hypothesize that a reduction in bony labyrinth disparity is indicative of the underlying genetic variation resulting from bottleneck events. We apply a deformation-based geometric morphometric approach to investigate semicircular canal and vestibule shape of a chronologically broad sample of individuals belonging to the Neanderthal lineage. Our results identify a significant reduction in disparity after the start of Marine Isotope Stage 5 supporting our hypothesis of a late bottleneck, possibly leading to the derived morphology of Late Pleistocene Neanderthals. In some structures, morphological phenotypic disparity can reflect underlying genetic variation. Here, the authors apply deformation-based geometric morphometrics to the Neanderthal clade bony labyrinth to identify a disparity reduction around MIS5, possibly pointing to a population bottleneck.

This paper introduces a Deep Learning (DL) framework to localize landmark coordinates within the semicircular canals in Computed Tomography (CT) scans of the temporal bone. These landmarks can be consistently defined across patients and imaging modalities and as such can serve as a means of forming a common coordinate system. We propose a DL based framework for automating the landmark selection process. We establish the accuracy of the methods using Bone Beam CT scans of the temporal bone of 20 patients and landmarks selected by 3 human experts as the ground truth. We show that the error rates are similar to the levels of variation in landmark selection achieved by human experts. We further validated the method on CT scans from 14 additional patients, demonstrating that the accuracy remains within clinically acceptable parameters.

The vestibular system detects head motion to coordinate vital reflexes and provide our sense of balance and spatial orientation. A long-standing hypothesis has been that projections from the central vestibular system back to the vestibular sensory organs (i.e., the efferent vestibular system) mediate adaptive sensory coding during voluntary locomotion. However, direct proof for this idea has been lacking. Here we recorded from individual semicircular canal and otolith afferents during walking and running in monkeys. Using a combination of mathematical modeling and nonlinear analysis, we show that afferent encoding is actually identical across passive and active conditions, irrespective of context. Thus, taken together our results are instead consistent with the view that the vestibular periphery relays robust information to the brain during primate locomotion, suggesting that context-dependent modulation instead occurs centrally to ensure that coding is consistent with behavioral goals during locomotion. Using experimental and computational approaches the authors show that the vestibular efferent system does not modulate peripheral coding during locomotion. Instead, vestibular afferents unambiguously convey information in a context independent manner.

Nodosauridae is a group of thyreophoran dinosaurs characterized by a collar of prominent osteoderms. In comparison to its sister group, the often club-tailed ankylosaurids, a different lifestyle of nodosaurids could be assumed based on their neuroanatomy and weaponry, e.g., regarding applied defensive strategies. The holotype of the nodosaurid Struthiosaurus austriacus consists of a single partial braincase from the Late Cretaceous of Austria. Since neuroanatomy is considered to be associated with ecological tendencies, we created digital models of the braincase based on micro-CT data. The cranial endocast of S. austriacus generally resembles those of its relatives. A network of vascular canals surrounding the brain cavity further supports special thermoregulatory adaptations within Ankylosauria. The horizontal orientation of the lateral semicircular canal independently confirms previous appraisals of head posture for S. austriacus and, hence, strengthens the usage of the LSC as proxy for habitual head posture in fossil tetrapods. The short anterior and angular lateral semicircular canals, combined with the relatively shortest dinosaurian cochlear duct known so far and the lack of a floccular recess suggest a rather inert lifestyle without the necessity of sophisticated senses for equilibrium and hearing in S. austriacus . These observations agree with an animal that adapted to a comparatively inactive lifestyle with limited social interactions.

Objective This study investigates the importance of bone density, surface area, and diameter of anatomical structures of the superior semicircular canal (SSC), lateral semicircular canal (LSC), posterior semicircular canal (PSC), utricle, and saccule in patients diagnosed with superior semicircular canal dehiscence (SSCD). Materials and methods The bone density, surface area, and diameter of SSC, LSC, PSC, utricle, and saccule were measured and compared between the SSCD group and control group. Fifteen ears in the SSCD group and 60 ears in the control group were evaluated. Additionally, within the SSCD group, the dehiscent and healthy sides were evaluated independently. Results SSC’s bone density was significantly lower in the SSCD group compared to the control group ( p  = 0.008). No significant differences were found in surface area and diameter between the groups ( p  > 0.05). While most of the anatomical structures showed no significant difference in bone density between dehiscent and healthy ears ( p  > 0.05), SSC bone density was significantly lower in affected ears ( p  = 0.000) in SSCD group. Conclusion Based on the data obtained in this study, bone density and anatomical structure may be useful in patients diagnosed with SSCD.

The vertebrate vestibular system is crucial for balance and navigation, and the evolution of its form and function in relation to species’ lifestyle and mode of locomotion has been the focus of considerable recent study. Most research, however, has concentrated on aboveground mammals, with much less published on subterranean fauna. Here, we explored variation in anatomy and sensitivity of the semicircular canals among 91 mammal species, including both subterranean and non-subterranean representatives. Quantitative phylogenetically informed analyses showed significant widening of the canals relative to radius of curvature in subterranean species. A relative canal width above 0.166 indicates with 95% certainty that a species is subterranean. Fluid–structure interaction modelling predicted that canal widening leads to a substantial increase in canal sensitivity; a reasonably good estimation of the absolute sensitivity is possible based on the absolute internal canal width alone. In addition, phylogenetic comparative modelling and functional landscape exploration revealed repeated independent evolution of increased relative canal width and anterior canal sensitivity associated with the transition to a subterranean lifestyle, providing evidence of parallel adaptation. Our results suggest that living in dark, subterranean tunnels requires good balance and/or navigation skills which may be facilitated by more sensitive semicircular canals.

Animal locomotion causes head rotations, which are detected by the semicircular canals of the inner ear. Morphologic features of the canals influence rotational sensitivity, and so it is hypothesized that locomotion and canal morphology are functionally related. Most prior research has compared subjective assessments of animal “agility” with a single determinant of rotational sensitivity: the mean canal radius of curvature (R). In fact, the paired variables of R and body mass are correlated with agility and have been used to infer locomotion in extinct species. To refine models of canal functional morphology and to improve locomotor inferences for extinct species, we compare 3D vector measurements of head rotation during locomotion with 3D vector measures of canal sensitivity. Contrary to the predictions of conventional models that are based upon R , we find that axes of rapid head rotation are not aligned with axes of either high or low sensitivity. Instead, animals with fast head rotations have similar sensitivities in all directions, which they achieve by orienting the three canals of each ear orthogonally (i.e., along planes at 90° angles to one another). The extent to which the canal configuration approaches orthogonality is correlated with rotational head speed independent of body mass and phylogeny, whereas R is not.

The semicircular canals (SCs), part of the vestibular apparatus of the inner ear, are directly involved in the detection of angular motion of the head for maintaining balance, and exhibit adaptive patterns for locomotor behaviour. Consequently, they are generally believed to show low levels of intraspecific morphological variation, but few studies have investigated this assumption. On the basis of high-resolution computed tomography, we present here, to our knowledge, the first comprehensive study of the pattern of variation of the inner ear with a focus on Xenarthra. Our study demonstrates that extant three-toed sloths show a high level of morphological variation of the bony labyrinth of the inner ear. Especially, the variation in shape, relative size and angles of their SCs greatly differ from those of other, faster-moving taxa within Xenarthra and Placentalia in general. The unique pattern of variation in three-toed sloths suggests that a release of selection and/or constraints on their organ of balance is associated with the observed wide range of phenotypes. This release is coincident with their slow and infrequent locomotion and may be related, among other possible factors, to a reduced functional demand for a precise sensitivity to movement.