title: Orientation of the lateral semicircular canal in Xenarthra and its links with head posture and phylogeny.
abstract: The orientation of the semicircular canals of the inner ear in the skull of vertebrates is one of the determinants of the capacity of this system to detect a given rotational movement of the head. Past functional studies on the spatial orientation of the semicircular canals essentially focused on the lateral semicircular canal (LSC), which is supposedly held close to horizontal during rest and/or alert behaviors. However, they generally investigated this feature in only a few and distantly related taxa. Based on 3D-models reconstructed from µCT-scans of skulls, we examined the diversity of orientations of the LSC within one of the four major clades of placental mammals, that is, the superorder Xenarthra, with a data set that includes almost all extant genera and two extinct taxa. We observed a wide diversity of LSC orientations relative to the basicranium at both intraspecific and interspecific scales. The estimated phylogenetic imprint on the orientation of the LSC was significant but rather low 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. 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 nose-down head posture. It also portrayed a more complex situation for sloths and anteaters. Finally, we also demonstrate that the conformation of the cranial vault and nuchal crests as well as the orientation of the posterior part of the petrosal may covary with the LSC orientation in Xenarthra. Possible inferences for the head postures of extinct xenarthrans such as giant ground sloths are discussed in the light of these results.
authors.affiliation: Department of Origines et évolution, Sorbonne Universités, CR2P, UMR CNRS 7207, Univ Paris 06, Muséum national d'Histoire naturelle, 8 rue Buffon, Paris, 75005, France.
authors.forename: Florence
authors.initials: F
authors.lastname: Coutier
authors.affiliation: Department of Forme, Institut des Sciences de l'Evolution de Montpellier, Université Montpellier, CNRS, IRD, EPHE, Cc 064; place Eugène Bataillon, Montpellier Cedex 5, 34095, France.
authors.forename: Lionel
authors.initials: L
authors.lastname: Hautier
authors.affiliation: Department of Origines et évolution, Institut de Systématique, Évolution, Biodiversité (ISYEB) - UMR 7205 - CNRS, MNHN, UPMC, EPHE- Muséum national d'Histoire naturelle - Sorbonne Universités, 57 rue Cuvier, CP 30, 75005, Paris, France.
authors.forename: Raphaël
authors.initials: R
authors.lastname: Cornette
authors.affiliation: Humboldt-Universität, AG Morphologie und Formengeschichte, Bild Wissen Gestaltung - ein interdisziplinäres Labor & Institut für Biologie, Philippstraße, 12/13, Berlin, D-10115, Germany.
authors.forename: Eli
authors.identifier: 0000-0003-1474-9613
authors.initials: E
authors.lastname: Amson
authors.affiliation: Department of Origines et évolution, Sorbonne Universités, CR2P, UMR CNRS 7207, Univ Paris 06, Muséum national d'Histoire naturelle, 8 rue Buffon, Paris, 75005, France.
authors.forename: Guillaume
authors.identifier: 0000-0002-3200-1548
authors.initials: G
authors.lastname: Billet
mesh_terms: D000818:Animals; D006257:Head; D010802:Phylogeny; D011187:Posture; D012665:Semicircular Canals / Q000033:anatomy & histology*; D004490:Xenarthra / Q000033:anatomy & histology* / Q000145:classification
keywords: bony labyrinth; fossil; inner ear; mammalia; morphometry