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Session Schedule & Abstracts

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Sunday 3rd July, 2016

Symposium: Show me your ear - The inner and middle ear in vertebrates 2

Room: Salon G   11:30 am–1:00 pm

Moderator(s): C. Pfaff, J. A. Schultz, & R. Schellhorn
EAR2-1  11:30 am  Functional morphological adaptations of the bony labyrinth in marsupials (Mammalia: Theria) . Pfaff C.*, University of Vienna, Department of Palaeontology, Austria; Kaineder G., University of Vienna, Department of Palaeontology, Austria; Czerny S., University of Vienna, Department of Palaeontology, Austria; Nagel D., University of Vienna, Department of Palaeontology, Austria; Kriwet J., University of Vienna, Department of Palaeontology, Austria
Abstract: Diprotodontia represents the largest and ecologically most distinct order of marsupials occurring in Australasian with almost 125 extant species. They are highly divers in size, locomotion (gliding, hopping, subterranean), habitat preferences (rain forests, arid areas), feeding (omnivorous, carnivorous, insectivorous), but also activity pattern (nocturnal, diurnal). The spatial orientation in the habitat and therefore the three-dimensional space is detected by the vestibular system of the inner ear, more precisely by the three semicircular canals (anterior, posterior, lateral), which are enclosed by the bony labyrinth. Previous studies of mammals were focusing on the functional morphological adaptations and the corresponding link between the morphology of the semicircular canals and the locomotion mode of the investigated taxa. In this study, we are investigating the bony labyrinth of 26 diprotodontian marsupial mammals of almost all genera with non-invasive micro-CT scanning and 3D reconstructions with an additional standardization of the measurements prior to statistical analyses, successfully applied in squirrels, to elucidate the functional morphological signal of the bony labyrinth. For reconstructing the ancestral state in Theria, three species of marsupials of South America were additionally included. In the principal component analyses, we found a clear distinction of arboreal and hopping species with an overlapping space of gliding and fossorial taxa. The highest loadings of this functional distinction are clearly found in the diameter of the semicircular canals, whereas the overall shape (height, width, length) of the semicircular canals is less important. Additionally, the investigated arboreal and fossorial species of South America are nested in the morphospace of the Australasian taxa. In future, by including fossil specimens of marsupials in this database, the locomotion mode of extinct taxa can be postulated without any evidence of postcranial material.

EAR2-2  11:45 am  Head posture and orientation of the lateral semicircular canal in xenarthrans (Mammalia). Coutier F, CR2P, Museum national d'Histoire naturelle, Paris, France; Hautier L, ISEM, University of Montpellier, France; Cornette R, ISYEB, Museum national d'Histoire naturelle, Paris, France; Amson E, Humboldt-Universitaet, Berlin, Germany; Billet G*, CR2P, Museum national d'Histoire naturelle, Paris, France
Abstract: The semicircular canal system of the inner ear is specialized for the detection of rotational accelerations and decelerations of the head. The orientation of the semicircular canals is one of the determinants of the capacity of this system to detect a given rotational movement. As a result, their position in the basicranium is highly constrained. Due to its potential link to the head posture, past studies on the orientation of the semicircular canals essentially focused on the lateral canal, which is supposedly held close to horizontal during rest and/or alert behaviors. Until now, functional studies on the orientation of the lateral semicircular canal (LSC) mainly focused on a limited number of taxa, often distantly related. Based on 3D models reconstructed from µCT-scans of skulls, we investigated the diversity of orientations of the LSC within one of the four major clades of placental mammals, i.e. the superorder Xenarthra, with a dataset that includes almost all extant genera and two fossil taxa (Megatherium, Pelecyodon). We observed a wide range of LSC orientations relative to the basicranium at both intra- and inter-specific scales. The estimated phylogenetic imprint on the orientation of the LSC was moderate within the superorder, though some phylogenetic conservatism was detected for armadillos that were characterized by a strongly tilted LSC. A convergence between extant suspensory sloths was also detected, both genera showing a weakly tilted LSC compared to the basicranium. Our preliminary analysis of usual head posture in extant xenarthrans (based on photographs of living animals) further revealed that the LSC orientation in armadillos is congruent with a strongly tilted head, but portrayed a more complex situation for sloths and anteaters. Several aspects of the posterior part of the skull, such as its relative height, also appeared to covary with the LSC orientation in Xenarthra and are likely related to functional and/or developmental constraints.

EAR2-3  12:00 pm  Bony labyrinth of Carnivora (Mammalia): the significance of phylogeny and the sensorial adaptation to aquatic environments. Grohe C.*, American Museum of Natural History; Tseng Z.J., American Museum of Natural History; Lebrun R., Institut des Sciences de l'Evolution de Montpellier; Boistel R., Universite de Poitiers; Flynn J.J., American Museum of Natural History
Abstract: The bony labyrinth is an osseous structure surrounding the inner ear, a primary sensorial organ involved in hearing, body perception in space, and balance in vertebrates. We investigated the influence of phylogenetic relationships and locomotor patterns on shape variation of the bony labyrinth in carnivoran mammals. We chose musteloids as a model group (skunks, red panda, coatis, raccoons, badgers, martens, otters, etc.) as it constitutes the most species-rich superfamily among Carnivora and it includes taxa with a wide array of locomotory styles (semi-fossorial, semi-aquatic, scansorial, arboreal, and generalized terrestrial forms). We reconstructed virtual bony labyrinths of 31 species based on X-ray microCT data of basicrania and we characterized their shape using 3D geometric morphometrics. PCA from shape data show distinct morphospaces between the four traditionally recognized families of musteloids (Mephitidae, Procyonidae, Ailuridae, Mustelidae). The phylogenetic variation of bony labyrinth shape in musteloids is associated with the size and curvature of the semicircular canals, angles between canals, presence or absence of a secondary common crus, degree of lateral compression of the vestibule, orientation of the cochlea relative to the semicircular canals, proportions of the cochlea, and degree of curvature of its turns. We also detected significant differences in the shape of the vestibular system between semi-aquatic and non-aquatic musteloids: otters and minks display an oval rather than circular anterior canal, sinuous rather than straight lateral canal, and acute rather than straight angle between the posterior and lateral semicircular canals compared to the remaining musteloid sample. Those modifications could be related to the sensorial adaptation of Carnivora for detecting head motion in aquatic environment and will be compared to the shape variation observed in Pinnipedia (seals, sea lions, walrus).

EAR2-4  12:15 pm  Morphological diversity among the inner ears of extinct and extant baleen whales (Cetacea: Mysticeti). Ekdale E.G.*, San Diego State University
Abstract: The ears of cetaceans are of special interest given the polarity of auditory physiology between the two major extant clades—the high-frequency sensitive Odontoceti and low-frequency sensitive Mysticeti. Our knowledge of the evolution and phylogeny of mysticetes is at a point where we can investigate the diverse morphologies of the inner ear of baleen whales through time, as well as explore functional diversity among mysticete species. Landmark-based 3D geometric morphometric analyses were performed to investigate the morphologic diversity of the bony labyrinths of the inner ears of extinct and exant mysticetes in comparison with other cetaceans. Principal component analyses (PCAs) show that the cochlear morphospace of odontocetes is tangential to that of mysticetes but is completely separated from mysticetes when semicircular canal landmarks are included. The majority of cochlear variation, including number of coils and graded curvature among successive turns, is related to auditory threshold frequencies. The cochlea of the archaeocete Zygorhiza kochii plots within the morphospace of mysticetes, suggesting that mysticetes possess ancestral cochlear morphology, and likely ancestral cochlear physiology. PCAs indicate a large degree of variation among mysticete species, suggesting that there are multiple hearing regimes among mysticetes, as has been demonstrated for odontocetes and hypothesized for mysticetes based on behavioral observations. Most of the variation among the semicircular canals is related to shape and orientation of the lateral semicircular canal, which is sensitive to yaw rotations (around a vertical axis). Semicircular canal variation may correspond to differences in locomotor behaviors. However, cochlear shape is phylogenetically informative for Neoceti and Chaeomysticeti (edentulous mysticetes), and the semicircular canals for multiple cetacean clades, which indicates that the form of the inner ear cannot be explained by function alone.

EAR2-5  12:30 pm  Hooves on the roof: the ear region of Diplobune minor, an arboreal artiodactyl from the Early Oligocene of France. Orliac M.J.*, Institut des Sciences de l'Evolution; Brualla N., Institut des Sciences de l'Evolution; Assemat A., Institut des Sciences de l'Evolution; Guignard M., Institut des Sciences de l'Evolution; Lihoreau F., Institut des Sciences de l'Evolution
Abstract: Apart from cetaceans, modern artiodactyls all walk the ground on their four feet. Among extinct taxa, Anoplotheriinae which lived during mid-Cenozoic times (40-30 million years ago) in Europe, show a unique postcranial morphology with an unusually large finger II and a lack of finger V on the hand and foot, a very mobile elbow articulation, and an uncommon orientation of the forelimbs and hind limbs. This peculiar morphology led to various hypotheses regarding their locomotion, from semi-aquatic to partly arboreal, or partly bipedal. Here we study the middle and inner ear morphology of Diplobune minor, a medium-sized anoplotheriid from the locality of Itardies (Early Oligocene, MP23, Quercy, France) through a case study of both in situ and isolated petrosals. This work allows for describing the stapes, the petrosal, and the bony labyrinth of this extinct taxon. The characteristics of the cast of the bony labyrinth indicates that D. minor had hearing capabilities similar to these of the extant goat (neither high nor low frequency specialist). The vestibular apparatus shows an unexpected variation of the shape and length of the semicircular canals that would support the hypothesis that D. minor was a slow tree-dwelling animal.

EAR2-6  12:45 pm  3D geometric morphometrics and cladistics analyses of the tragulid bony labyrinth: morphological variability and implications for ruminant phylogeny. Costeur L*, Natural History Museum Basel, Switzerland; Mennecart B, Natural History Museum Basel, Switzerland
Abstract: The bony labyrinth is known for its phylogenetic relevance. However, it has been vastly understudied in ruminants. We analyse sets of bony labyrinths of the three living tragulid genera (traguline ruminants) including Tragulus kanchil (juvenile and a late foetus stage), T. napu, Hyemoschus aquaticus, and Moschiola meminna. We use 3D geometric morphometrics to capture most of the bony-labyrinth shape. Through a PCA of the 3D data we show that intergenera disparity is higher than intragenera variability. Intraspecific variability is also observed (e.g. shape and extent of the lateral semi-circular canal, size and shape of the common crus). The late foetal stage plots slightly apart from the other T. kanchil specimens, but it remains identifiable at the species level. Issues related to timing of ossification of some parts (mostly canals) may partly account for this. However, early ontogenetic stages (foetus and post-natal) are not significantly different from adult stages (shape and size). The bony labyrinth in ruminants is fully formed before birth and its size and volume does not significantly change from this point on. Incorporating juvenile specimens in palaeontological studies is thus not problematic since they fall within the morphological range observed in adults. We run a cladistics analysis comparing all living tragulid genera and the fossil tragulid Dorcatherium crassum (ca. 15 Ma) to Pecora. Our study identifies new synapormorphies of the family Tragulidae based only on petrosal bone and bony labyrinth. This phylogenetic analysis confirms previous morphological and molecular analyses (e.g. sister-taxa relationship of Tragulus and Moschiola). This study shows the potential of the ruminant ear region and more specifically of the bony labyrinth in phylogenetic studies. Both shape analysis and discrete morphological characters are useful to decipher phylogenetic relationships. Study supported by the SNF project 200021-159854.

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