[en] The distal limb of many hooved mammals (ungulates) has become highly specialised, with tendonised muscles and elongate bones and ligaments. Several clades of ungulates retain fleshy, muscularised distal forelimbs; these include hippopotamuses, rhinoceroses, and tapirs. Of these species, tapirs (Tapiridae: Tapirus) represent the most plesiomorphic manus anatomy for its higher taxonomic group (Perissodactyla); the tetradactyl manus of tapirs is reminiscent of the earliest members of the lineages leading to modern horses (equids) and rhinocerotids. Within the tapir manus, osteological evidence indicates clear differences in load distribution, digit use during locomotion, and phylogenetic signal in the shape of certain bony elements. To date, no quantitative investigation has ever been performed to explore differences in the muscular anatomy of the tapir distal forelimb (manus). Here, we conducted a comparative muscle architecture quantification of the muscles which are intrinsic to the tapir manus, across all four extant species (Tapirus indicus, T. bairdii, T. pinchaque, T. terrestris). Despite limited sample sizes, we observed notable variation across the different species with regard to the force-generating potential of the muscles (based on physiological cross-sectional area, PCSA) and the shortening range of each muscle (based on fascicle length). High force-generating capacities were recovered for the interosseus muscles (preventing hyperextension) for the third and fourth digits, as may be expected for a mesaxonic manus such as that of Tapirus. Our results also indicate subtle differences in patterns of force-generating potential in the interosseus muscles between specimens housed in captivity and those from the wild, specifically living in upland rainforest and exhibiting ranging behaviour up and downhill on a regular basis. These data offer tantalising insights into the variation in the force-excursion relationship in the muscles of the ungulate manus, providing both qualitative and quantitative information for veterinarians, biologists, and palaeontologists investigating perissodactyl locomotor anatomy and evolution.
Maclaren, James ; Université de Liège - ULiège > Département de géologie > Evolution and diversity dynamics lab ; Department of Biology, Universiteit Antwerpen, Building D, Campus Drie Eiken, Universiteitsplein, Wilrijk, Antwerp, Belgium ; Palaeobiosphere Evolution Lab, Institute of Natural Sciences, Brussels, Belgium
Corssmit, Eva; Laboratorio de Anatomía Animal, Escuela de Medicina Veterinaria, Universidad Nacional de Costa Rica, Heredia, Costa Rica
MacMillan, Martha ; Zoology Preparation Lab, Denver Museum of Nature and Science, Denver, CO, USA
Rojas-Jimenez, Jorge ; Warnell School of Forestry & Natural Resources, University of Georgia, Athens, GA, USA ; TapirVet, San José, Costa Rica
Language :
English
Title :
A Quantitative Analysis of the Manus Musculature in Tapirs (Perissodactyla: Tapiridae).
The authors would like to thank Sandra Nauwelaerts, Ellen Goosenaerts, Denise Vogel, Chris Van Ginneken (UAntwerpen); John Demboski, Andie Carrillo, Kristen MacKenzie, Garth Spellman (DMNS); Liza Dadone and the staff of Cheyenne Mountain Zoo; Francis Vercammen and the staff of Antwerp Zoo (KMDA); Alex Larsson, Bim Boijsen, Linda Berggren and the staff of Kolm\u00E5rden Wildlife Park; park rangers from the National System of Conservation Areas (SINAC) at the National Park Los Quetzales (education & awareness), staff from Panthera Costa Rica and Don Eladio (roadkill reporting), and the Permit Office for permit support via University of Georgia (UGA) and the TapirVet Project. We would like to give special thanks for assistance during dissections to: Eleesha Annear (T. terrestris dissection) and Brianna McHorse (T. indicus dissection); technician Heiner Serrano, and the students from the C\u00E1tedra de Anatom\u00EDa Animal from the Escuela de Medicina Veterinaria (EMV) at the Universidad Nacional de Costa Rica (UNA) (T. bairdii dissection). The authors also thank professors Andreia Passos Pequeno (UNA) and Peter Aerts (UAntwerpen) for constructive discussions on biomechanical methodology and musculoskeletal descriptions, and two annonymous reviewers for their valuable comments throughout the review process. This study was financially supported by doctoral (11Y7615N) and post-doctoral (12V8422N) fellowships from the FWO (Fonds Wetenschappelijk Onderzoek), an FWO Short-Stay Travel Grant (Denver, 2022) (K207322N), a Company of Biologists Travel Grant (Kolm\u00E5rden, 2023) (all JAM).This study was financially supported by doctoral (11Y7615N) and post\u2010doctoral (12V8422N) fellowships from the FWO (Fonds Wetenschappelijk Onderzoek), an FWO Short\u2010Stay Travel Grant (Denver, 2022) (K207322N), a Company of Biologists Travel Grant (Kolm\u00E5rden, 2023) (all JAM).
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