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Billet G, Hautier L, Lebrun R. Morphological diversity of the bony labyrinth (inner ear) in extant Xenarthrans and its relation to phylogeny. J Mammal 2015. [DOI: 10.1093/jmammal/gyv074] [Citation(s) in RCA: 35] [Impact Index Per Article: 3.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/30/2023] Open
Abstract
Abstract
We present a survey of the morphological diversity of the bony labyrinth of the inner ear in Xenarthra, including the fossil ground sloth Megatherium. Using a combination of traditional and geometric morphometrics, correlation analyses, and qualitative observations, we attempt to extract independent and informative phylogenetic characters of the bony labyrinth for the superorder. Geometric morphometric analyses demonstrate a strong imprint of phylogenetic history on the shape of the bony labyrinth of xenarthrans and a weak influence of allometry. Discrete characters mapped on a consensus cladogram for xenarthrans show support for many traditional nodes within the superorder and may also provide critical information for problematic nodes within Cingulata. A relatively large lateral semicircular canal may, for instance, represent a synapomorphy for the molecular clade allying fairy armadillos (Chlamyphorinae) to the Tolypeutinae. Striking convergences were detected when comparing Megatherium, the giant ground sloth, with extant armadillos and Chlamyphorus, the pink fairy armadillo, with the extant three- and two-toed sloths. These findings have the potential to help understand the phylogenetic relationships of fossil xenarthrans.
Presentamos un estudio de la diversidad morfológica del laberinto óseo del oído interno de los xenartros, incluyendo el perezoso fósil Megatherium. Utilizamos una combinación de morfométrica tradicional y geométrica, análisis de correlación y observaciones cuantitativas para intentar extraer caracteres filogenéticos independientes e informativos del laberinto óseo para el superorden. Los análisis geométricos morfométricos muestran una fuerte impronta de la historia filogenética de la forma del laberinto óseo de los xenartros y una baja influencia de la alometría. Los caracteres discretos mapeados en un cladograma de consenso para xenartros apoyan varios nodos tradicionales dentro del superorden y podrían también brindar información importante para los nodos problemáticos dentro de los Cingulata. Un canal semicircular lateral relativamente largo podría, por ejemplo, representar una sinapomorfía que apoye el clado molecular que une a los pichiciegos con los Tolypeutinae. Se hallaron notables convergencias al comparar Megatherium con los armadillos actuales, y Chlamyphorus con los perezosos actuales. Estos hallazgos tienen el potencial para ayudar a entender las relaciones filogenéticas de los xenartros fósiles.
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Affiliation(s)
- Guillaume Billet
- CR2P, UMR CNRS 7207, CP 38, Muséum national d’Histoire naturelle, Univ Paris 06, 8 rue Buffon, 75005 Paris, France (GB)
| | - Lionel Hautier
- Laboratoire de Paléontologie, Institut des Sciences de l’Évolution de Montpellier (CNRS, UM2, IRD, EPHE), c.c. 064, Université Montpellier, Place Eugène Bataillon, 34095 Montpellier Cedex 05, France (LH, RL)
| | - Renaud Lebrun
- Laboratoire de Paléontologie, Institut des Sciences de l’Évolution de Montpellier (CNRS, UM2, IRD, EPHE), c.c. 064, Université Montpellier, Place Eugène Bataillon, 34095 Montpellier Cedex 05, France (LH, RL)
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Crumpton N, Kardjilov N, Asher RJ. Convergence vs. Specialization in the ear region of moles (Mammalia). J Morphol 2015; 276:900-14. [PMID: 25858660 DOI: 10.1002/jmor.20391] [Citation(s) in RCA: 11] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/18/2014] [Revised: 03/03/2015] [Accepted: 03/10/2015] [Indexed: 11/05/2022]
Abstract
We investigated if and how the inner ear region undergoes similar adaptations in small, fossorial, insectivoran-grade mammals, and found a variety of inner ear phenotypes. In our sample, afrotherian moles (Chrysochloridae) and the marsupial Notoryctes differ from most other burrowing mammals in their relatively short radii of semicircular canal curvature; chrysochlorids and fossorial talpids share a relatively long interampullar width. Chrysochlorids are unique in showing a highly coiled cochlea with nearly four turns. Extensive cochlear coiling may reflect their greater ecological dependence on low frequency auditory cues compared to talpids, tenrecids, and the marsupial Notoryctes. Correspondingly, the lack of such extensive coiling in the inner ear of other fossorial species may indicate a greater reliance on other senses to enable their fossorial lifestyle, such as tactile sensation from vibrissae and Eimer's organs. The reliance of chrysochlorids on sound is evident in the high degree of coiling and in the diversity of its mallear types, and may help explain the lack of any semiaquatic members of that group. The simplest mallear types among chrysochlorids are not present in the basal-most members of that clade, but all extant chrysochlorids investigated to date exhibit extensive cochlear coiling. The chrysochlorid ear region thus exhibits mosaic evolution; our data suggest that extensive coiling evolved in chrysochlorids prior to and independently of diversification in middle ear ossicle size and shape.
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Affiliation(s)
- Nick Crumpton
- Department of Zoology, University of Cambridge, Downing Street, CB2 3EJ, UK.,Natural History Museum, Cromwell Road, London, SW7 5BD, UK
| | - Nikolay Kardjilov
- Helmholtz-Zentrum Berlin, Hahn-Meitner-Platz 1, D-14109, Berlin, Germany
| | - Robert J Asher
- Department of Zoology, University of Cambridge, Downing Street, CB2 3EJ, UK
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Billet G, de Muizon C, Schellhorn R, Ruf I, Ladevèze S, Bergqvist L. Petrosal and inner ear anatomy and allometry amongst specimens referred to Litopterna (Placentalia). Zool J Linn Soc 2015. [DOI: 10.1111/zoj.12219] [Citation(s) in RCA: 30] [Impact Index Per Article: 3.3] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/25/2022]
Affiliation(s)
- Guillaume Billet
- Steinmann-Institut für Geologie; Mineralogie und Paläontologie; Rheinische Friedrich-Wilhelms-Universität Bonn; Nussallee 8 53115 Bonn Germany
- CR2P - UMR 7207 CNRS; MNHN; Univ Paris 06 - Muséum national d'Histoire naturelle; 8 rue Buffon CP 38 75005 Paris France
| | - Christian de Muizon
- CR2P - UMR 7207 CNRS; MNHN; Univ Paris 06 - Muséum national d'Histoire naturelle; 8 rue Buffon CP 38 75005 Paris France
| | - Rico Schellhorn
- Steinmann-Institut für Geologie; Mineralogie und Paläontologie; Rheinische Friedrich-Wilhelms-Universität Bonn; Nussallee 8 53115 Bonn Germany
| | - Irina Ruf
- Steinmann-Institut für Geologie; Mineralogie und Paläontologie; Rheinische Friedrich-Wilhelms-Universität Bonn; Nussallee 8 53115 Bonn Germany
- Senckenberg Forschungsinstitut und Naturmuseum Frankfurt; Abteilung Paläoanthropologie und Messelforschung; Senckenberganlage 25 60325 Frankfurt am Main Germany
| | - Sandrine Ladevèze
- CR2P - UMR 7207 CNRS; MNHN; Univ Paris 06 - Muséum national d'Histoire naturelle; 8 rue Buffon CP 38 75005 Paris France
| | - Lilian Bergqvist
- Avenida Athos da Silveira Ramos; 274, bloco G; Centro de Ciências Matemáticas e da Natureza; Universidade Federal do Rio de Janeiro; Rio de Janeiro 21941-916 Brasil
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Ekdale EG, Racicot RA. Anatomical evidence for low frequency sensitivity in an archaeocete whale: comparison of the inner ear of Zygorhiza kochii with that of crown Mysticeti. J Anat 2014; 226:22-39. [PMID: 25400023 DOI: 10.1111/joa.12253] [Citation(s) in RCA: 32] [Impact Index Per Article: 3.2] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Accepted: 09/24/2014] [Indexed: 11/28/2022] Open
Abstract
The evolution of hearing in cetaceans is a matter of current interest given that odontocetes (toothed whales) are sensitive to high frequency sounds and mysticetes (baleen whales) are sensitive to low and potentially infrasonic noises. Earlier diverging stem cetaceans (archaeocetes) were hypothesized to have had either low or high frequency sensitivity. Through CT scanning, the morphology of the bony labyrinth of the basilosaurid archaeocete Zygorhiza kochii is described and compared to novel information from the inner ears of mysticetes, which are less known than the inner ears of odontocetes. Further comparisons are made with published information for other cetaceans. The anatomy of the cochlea of Zygorhiza is in line with mysticetes and supports the hypothesis that Zygorhiza was sensitive to low frequency noises. Morphological features that support the low frequency hypothesis and are shared by Zygorhiza and mysticetes include a long cochlear canal with a high number of turns, steeply graded curvature of the cochlear spiral in which the apical turn is coiled tighter than the basal turn, thin walls separating successive turns that overlap in vestibular view, and reduction of the secondary bony lamina. Additional morphology of the vestibular system indicates that Zygorhiza was more sensitive to head rotations than extant mysticetes are, which likely indicates higher agility in the ancestral taxon.
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Affiliation(s)
- Eric G Ekdale
- Department of Biology, San Diego State University, San Diego, CA, USA; Department of Paleontology, San Diego Natural History Museum, San Diego, CA, USA
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Hautier L, Billet G, Eastwood B, Lane J. Patterns of Morphological Variation of Extant Sloth Skulls and their Implication for Future Conservation Efforts. Anat Rec (Hoboken) 2014; 297:979-1008. [DOI: 10.1002/ar.22916] [Citation(s) in RCA: 23] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/18/2013] [Accepted: 02/18/2014] [Indexed: 11/06/2022]
Affiliation(s)
- Lionel Hautier
- Laboratoire de Paléontologie; Institut des Sciences de l'Evolution de Montpellier, UMR-CNRS 5554, Cc 064, Université de Montpellier 2, place Eugène Bataillon; Montpellier Cedex France
- Museum of Zoology; University of Cambridge; Cambridge UK
| | - Guillaume Billet
- Muséum national d'Histoire naturelle; CR2P-UMR 7207 CNRS, MNHN, Univ Paris 06, 57 rue Cuvier, CP; 38 75005 Paris France
| | | | - Jemima Lane
- Museum of Zoology; University of Cambridge; Cambridge UK
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Hill CA, Radovčić J, Frayer DW. Brief communication: Investigation of the semicircular canal variation in the Krapina Neandertals. AMERICAN JOURNAL OF PHYSICAL ANTHROPOLOGY 2014; 154:302-6. [DOI: 10.1002/ajpa.22506] [Citation(s) in RCA: 13] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Track Full Text] [Subscribe] [Scholar Register] [Received: 10/24/2013] [Accepted: 02/26/2014] [Indexed: 01/28/2023]
Affiliation(s)
- Cheryl A. Hill
- Department of Basic Medical Sciences; University of Arizona College of Medicine-Phoenix; Phoenix AZ 85004
| | - Jakov Radovčić
- Croatian Natural History Museum; Demetrova 1, 1000 Zagreb Croatia
| | - David W. Frayer
- Department of Anthropology; University of Kansas; 622 Fraser Hall Lawrence KS 66045
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Functional implications of ubiquitous semicircular canal non-orthogonality in mammals. PLoS One 2013; 8:e79585. [PMID: 24260256 PMCID: PMC3834179 DOI: 10.1371/journal.pone.0079585] [Citation(s) in RCA: 66] [Impact Index Per Article: 6.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/08/2013] [Accepted: 10/02/2013] [Indexed: 12/20/2022] Open
Abstract
The 'canonical model' of semicircular canal orientation in mammals assumes that 1) the three ipsilateral canals of an inner ear exist in orthogonal planes (i.e., orthogonality), 2) corresponding left and right canal pairs have equivalent angles (i.e., angle symmetry), and 3) contralateral synergistic canals occupy parallel planes (i.e., coplanarity). However, descriptions of vestibular anatomy that quantify semicircular canal orientation in single species often diverge substantially from this model. Data for primates further suggest that semicircular canal orthogonality varies predictably with the angular head velocities encountered in locomotion. These observations raise the possibility that orthogonality, symmetry, and coplanarity are misleading descriptors of semicircular canal orientation in mammals, and that deviations from these norms could have significant functional consequences. Here we critically assess the canonical model of semicircular canal orientation using high-resolution X-ray computed tomography scans of 39 mammal species. We find that substantial deviations from orthogonality, angle symmetry, and coplanarity are the rule for the mammals in our comparative sample. Furthermore, the degree to which the semicircular canals of a given species deviate from orthogonality is negatively correlated with estimated vestibular sensitivity. We conclude that the available comparative morphometric data do not support the canonical model and that its overemphasis as a heuristic generalization obscures a large amount of functionally relevant variation in semicircular canal orientation between species.
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Rager L, Hautier L, Forasiepi A, Goswami A, Sánchez-Villagra MR. Timing of cranial suture closure in placental mammals: Phylogenetic patterns, intraspecific variation, and comparison with marsupials. J Morphol 2013; 275:125-40. [DOI: 10.1002/jmor.20203] [Citation(s) in RCA: 31] [Impact Index Per Article: 2.8] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Revised: 04/05/2013] [Accepted: 08/21/2013] [Indexed: 01/21/2023]
Affiliation(s)
- Lisa Rager
- Paläontologisches Institut und Museum; Universität Zürich, Karl Schmid-Strasse 4; CH-8006 Zürich Switzerland
| | - Lionel Hautier
- Department of Zoology; University of Cambridge; Cambridge CB2 3EJ UK
- Laboratoire de Paléontologie; Institut des Sciences de l'Évolution (ISE-M, UMR-CNRS 5554), C.c. 64, Université Montpellier 2; Place Eugène Bataillon, F-34095 Montpellier Cedex 05 France
| | - Analía Forasiepi
- Paläontologisches Institut und Museum; Universität Zürich, Karl Schmid-Strasse 4; CH-8006 Zürich Switzerland
- CONICET, IANIGLA, CCT-Mendoza; Avda. Ruiz Leal s/n, 5500, Mendoza Mendoza Argentina
| | - Anjali Goswami
- Department of Genetics; Evolution and Environment, University College London; London UK
| | - Marcelo R. Sánchez-Villagra
- Paläontologisches Institut und Museum; Universität Zürich, Karl Schmid-Strasse 4; CH-8006 Zürich Switzerland
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Billet G, Germain D, Ruf I, de Muizon C, Hautier L. The inner ear of Megatherium and the evolution of the vestibular system in sloths. J Anat 2013; 223:557-67. [PMID: 24111879 DOI: 10.1111/joa.12114] [Citation(s) in RCA: 37] [Impact Index Per Article: 3.4] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Accepted: 08/29/2013] [Indexed: 11/29/2022] Open
Abstract
Extant tree sloths are uniquely slow mammals with a very specialized suspensory behavior. To improve our understanding of their peculiar evolution, we investigated the inner ear morphology of one of the largest and most popular fossil ground sloths, Megatherium americanum. We first address the predicted agility of this animal from the scaling of its semicircular canals (SC) relative to body mass, based on recent work that provided evidence that the size of the SC in mammals correlates with body mass and levels of agility. Our analyses predict intermediate levels of agility for Megatherium, contrasting with the extreme slowness of extant sloths. Secondly, we focus on the morphology of the SC at the inner ear scale and investigate the shape and proportions of these structures in Megatherium and in a large diversity of extant xenarthrans represented in our database. Our morphometric analyses demonstrate that the giant ground sloth clearly departs from the SC morphology of both extant sloth genera (Choloepus, Bradypus) and is in some aspects closer to that of armadillos and anteaters. Given the close phylogenetic relationships of Megatherium with the extant genus Choloepus, these results are evidence of substantial homoplasy of the SC anatomy in sloths. This homoplasy most likely corresponds to an outstanding convergent evolution between extant suspensory sloth genera.
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Affiliation(s)
- G Billet
- CR2P - UMR 7207 CNRS, MNHN, Univ Paris 06, Paris, France
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60
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Benoit J, Essid EM, Marzougui W, Khayati Ammar H, Lebrun R, Tabuce R, Marivaux L. New insights into the ear region anatomy and cranial blood supply of advanced stem Strepsirhini: evidence from three primate petrosals from the Eocene of Chambi, Tunisia. J Hum Evol 2013; 65:551-72. [PMID: 23938180 DOI: 10.1016/j.jhevol.2013.06.014] [Citation(s) in RCA: 16] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/19/2013] [Revised: 05/16/2013] [Accepted: 06/26/2013] [Indexed: 01/29/2023]
Abstract
We report the discovery of three isolated primate petrosal fragments from the fossiliferous locality of Chambi (Tunisia), a primate-bearing locality dating from the late early to the early middle Eocene. These fossils display a suite of anatomical characteristics otherwise found only in strepsirhines, and as such might be attributed either to Djebelemur or/and cf. Algeripithecus, the two diminutive stem strepsirhine primates recorded from this locality. Although damaged, the petrosals provide substantial information regarding the ear anatomy of these advanced stem strepsirhines (or pre-tooth-combed primates), notably the patterns of the pathway of the arterial blood supply. Using μCT-scanning techniques and digital segmentation of the structures, we show that the transpromontorial and stapedial branches of the internal carotid artery (ICA) were present (presence of bony tubes), but seemingly too small to supply enough blood to the cranium alone. This suggests that the ICA was not the main cranial blood supply in stem strepsirhines, but that the pharyngeal or vertebral artery primitively ensured a great part of this role instead, an arterial pattern that is reminiscent of modern cheirogaleid, lepilemurid lemuriforms and lorisiforms. This could explain parallel loss of the ICA functionality among these families. Specific measurements made on the cochlea indicate that the small strepsirhine primate(s) from Chambi was (were) highly sensitive to high frequencies and poorly sensitive to low frequencies. Finally, variance from orthogonality of the plane of the semicircular canals (SCs) calculated on one petrosal (CBI-1-569) suggests that Djebelemur or cf. Algeripithecus likely moved (at least its head) in a way similar to that of modern mouse lemurs.
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Affiliation(s)
- Julien Benoit
- Laboratoire de Paléontologie, Institut des Sciences de l'Évolution de Montpellier (ISE-M, UMR-CNRS 5554), c.c. 064, Université Montpellier 2, place Eugène Bataillon, F-34095 Montpellier Cedex 05, France.
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61
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Marugán-Lobón J, Chiappe LM, Farke AA. The variability of inner ear orientation in saurischian dinosaurs: testing the use of semicircular canals as a reference system for comparative anatomy. PeerJ 2013; 1:e124. [PMID: 23940837 PMCID: PMC3740149 DOI: 10.7717/peerj.124] [Citation(s) in RCA: 32] [Impact Index Per Article: 2.9] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/11/2013] [Accepted: 07/17/2013] [Indexed: 12/26/2022] Open
Abstract
The vestibular system of the inner ear houses three semicircular canals—oriented on three nearly-orthogonal planes—that respond to angular acceleration stimuli. In recent years, the orientation of the lateral semicircular canal (LSC) has been regularly used to determine skull orientations for comparative purposes in studies of non-avian dinosaurs. Such orientations have been inferred based on fixing the LSC to a common set of coordinates (parallel to the Earth’s horizon), given that the orientation to gravity of this sensory system is assumed constant among taxa. Under this assumption, the LSC is used as a baseline (a reference system) both to estimate how the animals held their heads and to describe craniofacial variation among dinosaurs. However, the available data in living birds (extant saurischian dinosaurs) suggests that the orientation of the LSC in non-avian saurischian dinosaurs could have been very variable and taxon-specific. If such were the case, using the LSC as a comparative reference system would cause inappropriate visual perceptions of craniofacial organization, leading to significant descriptive inconsistencies among taxa. Here, we used Procrustes methods (Geometric Morphometrics), a suite of analytical tools that compares morphology on the basis of shared landmark homology, to show that the variability of LSC relative to skull landmarks is large (ca. 50°) and likely unpredictable, thus making it an inconsistent reference system for comparing and describing the skulls of saurischian (sauropodomorph and theropod) dinosaurs. In light of our results, the lateral semicircular canal is an inconsistent baseline for comparative studies of craniofacial morphology in dinosaurs.
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Affiliation(s)
- Jesús Marugán-Lobón
- Unidad de Paleontología, Dpto. Biología, Universidad Autónoma de Madrid , Cantoblanco (Madrid) , Spain ; The Dinosaur Institute, Natural History Museum of Los Angeles County , Los Angeles, CA , USA
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62
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Straehl FR, Scheyer TM, Forasiepi AM, MacPhee RD, Sánchez-Villagra MR. Evolutionary patterns of bone histology and bone compactness in xenarthran mammal long bones. PLoS One 2013; 8:e69275. [PMID: 23874932 PMCID: PMC3706384 DOI: 10.1371/journal.pone.0069275] [Citation(s) in RCA: 49] [Impact Index Per Article: 4.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/12/2013] [Accepted: 06/06/2013] [Indexed: 11/19/2022] Open
Abstract
Bone microstructure reflects physiological characteristics and has been shown to contain phylogenetic and ecological signals. Although mammalian long bone histology is receiving increasing attention, systematic examination of the main clades has not yet been performed. Here we describe the long bone microstructure of Xenarthra based on thin sections representing twenty-two species. Additionally, patterns in bone compactness of humeri and femora are investigated. The primary bone tissue of xenarthran long bones is composed of a mixture of woven, parallel-fibered and lamellar bone. The vascular canals have a longitudinal, reticular or radial orientation and are mostly arranged in an irregular manner. Concentric rows of vascular canals and laminar organization of the tissue are only found in anteater bones. The long bones of adult specimens are marked by dense Haversian bone, a feature that has been noted for most groups of mammals. In the long bones of armadillos, secondary osteons have an oblique orientation within the three-dimensional bone tissue, thus resulting in their irregular shape when the bones are sectioned transversely. Secondary remodeling is generally more extensive in large taxa than in small taxa, and this could be caused by increased loading. Lines of arrested growth are assumed to be present in all specimens, but they are restricted to the outermost layer in bones of armadillos and are often masked by secondary remodeling in large taxa. Parameters of bone compactness show a pattern in the femur that separates Cingulata and Pilosa (Folivora and Vermilingua), with cingulates having a lower compactness than pilosans. In addition, cingulates show an allometric relationship between humeral and femoral bone compactness.
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Affiliation(s)
- Fiona R. Straehl
- Paläontologisches Institut und Museum, Universität Zürich, Zürich, Switzerland
| | - Torsten M. Scheyer
- Paläontologisches Institut und Museum, Universität Zürich, Zürich, Switzerland
| | | | - Ross D. MacPhee
- Vertebrate Zoology, American Museum of Natural History, New York, New York, United States of America
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63
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Ekdale EG. Comparative Anatomy of the Bony Labyrinth (Inner Ear) of Placental Mammals. PLoS One 2013; 8:e66624. [PMID: 23805251 PMCID: PMC3689836 DOI: 10.1371/journal.pone.0066624] [Citation(s) in RCA: 120] [Impact Index Per Article: 10.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/13/2012] [Accepted: 05/07/2013] [Indexed: 11/18/2022] Open
Abstract
BACKGROUND Variation is a naturally occurring phenomenon that is observable at all levels of morphology, from anatomical variations of DNA molecules to gross variations between whole organisms. The structure of the otic region is no exception. The present paper documents the broad morphological diversity exhibited by the inner ear region of placental mammals using digital endocasts constructed from high-resolution X-ray computed tomography (CT). Descriptions cover the major placental clades, and linear, angular, and volumetric dimensions are reported. PRINCIPAL FINDINGS The size of the labyrinth is correlated to the overall body mass of individuals, such that large bodied mammals have absolutely larger labyrinths. The ratio between the average arc radius of curvature of the three semicircular canals and body mass of aquatic species is substantially lower than the ratios of related terrestrial taxa, and the volume percentage of the vestibular apparatus of aquatic mammals tends to be less than that calculated for terrestrial species. Aspects of the bony labyrinth are phylogenetically informative, including vestibular reduction in Cetacea, a tall cochlear spiral in caviomorph rodents, a low position of the plane of the lateral semicircular canal compared to the posterior canal in Cetacea and Carnivora, and a low cochlear aspect ratio in Primatomorpha. SIGNIFICANCE The morphological descriptions that are presented add a broad baseline of anatomy of the inner ear across many placental mammal clades, for many of which the structure of the bony labyrinth is largely unknown. The data included here complement the growing body of literature on the physiological and phylogenetic significance of bony labyrinth structures in mammals, and they serve as a source of data for future studies on the evolution and function of the vertebrate ear.
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Affiliation(s)
- Eric G. Ekdale
- Department of Biology, San Diego State University, San Diego, California, United States of America
- Department of Paleontology, San Diego Natural History Museum, San Diego, California, United States of America
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64
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Davies KTJ, Bates PJJ, Maryanto I, Cotton JA, Rossiter SJ. The evolution of bat vestibular systems in the face of potential antagonistic selection pressures for flight and echolocation. PLoS One 2013; 8:e61998. [PMID: 23637943 PMCID: PMC3634842 DOI: 10.1371/journal.pone.0061998] [Citation(s) in RCA: 32] [Impact Index Per Article: 2.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/11/2012] [Accepted: 03/18/2013] [Indexed: 01/29/2023] Open
Abstract
The vestibular system maintains the body's sense of balance and, therefore, was probably subject to strong selection during evolutionary transitions in locomotion. Among mammals, bats possess unique traits that place unusual demands on their vestibular systems. First, bats are capable of powered flight, which in birds is associated with enlarged semicircular canals. Second, many bats have enlarged cochleae associated with echolocation, and both cochleae and semicircular canals share a space within the petrosal bone. To determine how bat vestibular systems have evolved in the face of these pressures, we used micro-CT scans to compare canal morphology across species with contrasting flight and echolocation capabilities. We found no increase in canal radius in bats associated with the acquisition of powered flight, but canal radius did correlate with body mass in bat species from the suborder Yangochiroptera, and also in non-echolocating Old World fruit bats from the suborder Yinpterochiroptera. No such trend was seen in members of the Yinpterochiroptera that use laryngeal echolocation, although canal radius was associated with wing-tip roundedness in this group. We also found that the vestibular system scaled with cochlea size, although the relationship differed in species that use constant frequency echolocation. Across all bats, the shape of the anterior and lateral canals was associated with large cochlea size and small body size respectively, suggesting differential spatial constraints on each canal depending on its orientation within the skull. Thus in many echolocating bats, it seems that the combination of small body size and enlarged cochlea together act as a principal force on the vestibular system. The two main groups of echolocating bats displayed different canal morphologies, in terms of size and shape in relation to body mass and cochlear size, thus suggesting independent evolutionary pathways and offering tentative support for multiple acquisitions of echolocation.
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Affiliation(s)
- Kalina T J Davies
- School of Biological and Chemical Sciences, Queen Mary University of London, London, United Kingdom.
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