87
views
0
recommends
+1 Recommend
0 collections
    3
    shares
      • Record: found
      • Abstract: found
      • Article: found
      Is Open Access

      Comparative Anatomy of the Bony Labyrinth (Inner Ear) of Placental Mammals

      research-article
      1 , 2 , *
      PLoS ONE
      Public Library of Science

      Read this article at

      Bookmark
          There is no author summary for this article yet. Authors can add summaries to their articles on ScienceOpen to make them more accessible to a non-specialist audience.

          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.

          Related collections

          Most cited references108

          • Record: found
          • Abstract: found
          • Article: not found

          The delayed rise of present-day mammals.

          Did the end-Cretaceous mass extinction event, by eliminating non-avian dinosaurs and most of the existing fauna, trigger the evolutionary radiation of present-day mammals? Here we construct, date and analyse a species-level phylogeny of nearly all extant Mammalia to bring a new perspective to this question. Our analyses of how extant lineages accumulated through time show that net per-lineage diversification rates barely changed across the Cretaceous/Tertiary boundary. Instead, these rates spiked significantly with the origins of the currently recognized placental superorders and orders approximately 93 million years ago, before falling and remaining low until accelerating again throughout the Eocene and Oligocene epochs. Our results show that the phylogenetic 'fuses' leading to the explosion of extant placental orders are not only very much longer than suspected previously, but also challenge the hypothesis that the end-Cretaceous mass extinction event had a major, direct influence on the diversification of today's mammals.
            Bookmark
            • Record: found
            • Abstract: found
            • Article: not found

            Resolution of the early placental mammal radiation using Bayesian phylogenetics.

            Molecular phylogenetic studies have resolved placental mammals into four major groups, but have not established the full hierarchy of interordinal relationships, including the position of the root. The latter is critical for understanding the early biogeographic history of placentals. We investigated placental phylogeny using Bayesian and maximum-likelihood methods and a 16.4-kilobase molecular data set. Interordinal relationships are almost entirely resolved. The basal split is between Afrotheria and other placentals, at about 103 million years, and may be accounted for by the separation of South America and Africa in the Cretaceous. Crown-group Eutheria may have their most recent common ancestry in the Southern Hemisphere (Gondwana).
              Bookmark
              • Record: found
              • Abstract: found
              • Article: not found

              Placental mammal diversification and the Cretaceous-Tertiary boundary.

              Competing hypotheses for the timing of the placental mammal radiation focus on whether extant placental orders originated and diversified before or after the Cretaceous-Tertiary (KT) boundary. Molecular studies that have addressed this issue suffer from single calibration points, unwarranted assumptions about the molecular clock, andor taxon sampling that lacks representatives of all placental orders. We investigated this problem using the largest available molecular data set for placental mammals, which includes segments of 19 nuclear and three mitochondrial genes for representatives of all extant placental orders. We used the ThorneKishino method, which permits simultaneous constraints from the fossil record and allows rates of molecular evolution to vary on different branches of a phylogenetic tree. Analyses that used different sets of fossil constraints, different priors for the base of Placentalia, and different data partitions all support interordinal divergences in the Cretaceous followed by intraordinal diversification mostly after the KT boundary. Four placental orders show intraordinal diversification that predates the KT boundary, but only by an average of 10 million years. In contrast to some molecular studies that date the rat-mouse split as old as 46 million years, our results show improved agreement with the fossil record and place this split at 16-23 million years. To test the hypothesis that molecular estimates of Cretaceous divergence times are an artifact of increased body size subsequent to the KT boundary, we also performed analyses with a "KT body size" taxon set. In these analyses, interordinal splits remained in the Cretaceous.
                Bookmark

                Author and article information

                Contributors
                Role: Editor
                Journal
                PLoS One
                PLoS ONE
                plos
                plosone
                PLoS ONE
                Public Library of Science (San Francisco, USA )
                1932-6203
                2013
                21 June 2013
                : 8
                : 6
                : e66624
                Affiliations
                [1 ]Department of Biology, San Diego State University, San Diego, California, United States of America
                [2 ]Department of Paleontology, San Diego Natural History Museum, San Diego, California, United States of America
                University of Maryland, United States of America
                Author notes

                Competing Interests: The author has declared that no competing interests exist.

                Analyzed the data: EGE. Wrote the paper: EGE.

                Article
                PONE-D-12-39373
                10.1371/journal.pone.0066624
                3689836
                23805251
                a27c931e-5a07-4abb-992b-a981337feb63
                Copyright @ 2013

                Ekdale. This is an open-access article distributed under the terms of the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original author and source are credited.

                History
                : 13 December 2012
                : 7 May 2013
                Page count
                Pages: 100
                Funding
                Research was supported by funding from the Jackson Schools of Geosciences at The University of Texas at Austin, the Texas Academy of Science, and the Paleontological Society. The University of Texas High-Resolution X-ray CT facility, at which CT data were collected, is funded by NSF EAR-034710. The funders had no role in study design, data collection and analysis, decision to publish, or preparation of the manuscript.
                Categories
                Research Article
                Biology
                Anatomy and Physiology
                Comparative Anatomy
                Developmental Biology
                Evolutionary Developmental Biology
                Evolutionary Biology
                Evolutionary Systematics
                Phylogenetics
                Neuroscience
                Sensory Systems
                Auditory System
                Zoology
                Animal Phylogenetics
                Comparative Anatomy
                Mammalogy

                Uncategorized
                Uncategorized

                Comments

                Comment on this article