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MacLaren JA. Looking back over the shoulder: New insights on the unique scapular anatomy of the tapir (Perissodactyla: Tapiridae). Anat Rec (Hoboken) 2024; 307:2121-2138. [PMID: 37966173 DOI: 10.1002/ar.25352] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/29/2023] [Revised: 11/03/2023] [Accepted: 11/05/2023] [Indexed: 11/16/2023]
Abstract
The musculoskeletal anatomy of the shoulder of many ungulates has been inferred from veterinary model taxa, with uniformity in muscle arrangements and attachment sites often assumed. In this study, I investigated the muscular and osteological anatomy of tapirs and their relatives (Perissodactyla: Tapiroidea), using a combination of gross dissection and digital imaging (photography and laser surface scanning). Dissections of three modern tapir species revealed that the m. infraspinatus originates from both supraspinous and infraspinous fossae for all species, lying on both sides of the distal scapular spine. The epimysial border between the m. supraspinatus and m. infraspinatus origin sites are marked in all species by an ossified ridge, sometimes extending the length of the scapular spine. This "supraspinous ridge" is clearly visible on the scapular surface of both modern and extinct Tapirus scapulae; however, the ridge does not appear present in any non-Tapirus tapiroids examined (e.g., Helaletes, Nexuotapirus), nor in other perissodactyls or artiodactyls. Moreover, the ridge exhibits a clearly distinct morphology in Tapirus indicus compared to all other Tapirus species examined. Combined, these findings indicate that the presence and position of the "supraspinous ridge" may represent a robust phylogenetic character for reconstructing relationships within tapiroids. Unfortunately, any functional locomotor outcomes or benefits of the m. infraspinatus straddling the scapular spine remains elusive. This study represents a firm reminder for anatomists, veterinarians, and paleontologists to (where possible) look beyond veterinary model systems when inferring musculoskeletal form or function in non-model organisms.
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Affiliation(s)
- Jamie A MacLaren
- Department of Biology, Universiteit Antwerpen, Wilrijk, Antwerp, Belgium
- Evolution & Diversity Dynamics Lab, UR Geology, Université de Liège, Liège, Belgium
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VAN Linden L, Stoops K, Dumbá LCCS, Cozzuol MA, Maclaren JA. Sagittal crest morphology decoupled from relative bite performance in Pleistocene tapirs (Perissodactyla: Tapiridae). Integr Zool 2023; 18:254-277. [PMID: 35048523 DOI: 10.1111/1749-4877.12627] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/28/2022]
Abstract
Bite force is often associated with specific morphological features, such as sagittal crests. The presence of a pronounced sagittal crest in some tapirs (Perissodactyla: Tapiridae) was recently shown to be negatively correlated with hard-object feeding, in contrast with similar cranial structures in carnivorans. The aim of this study was to investigate bite forces and sagittal crest heights across a wide range of modern and extinct tapirs and apply a comparative investigation to establish whether these features are correlated across a broad phylogenetic scope. We examined a sample of 71 specimens representing 15 tapir species (5 extant, 10 extinct) using the dry-skull method, linear measurements of cranial features, phylogenetic reconstruction, and comparative analyses. Tapirs were found to exhibit variation in bite force and sagittal crest height across their phylogeny and between different biogeographical realms, with high-crested morphologies occurring mostly in Neotropical species. The highest bite forces within tapirs appear to be driven by estimates for the masseter-pterygoid muscle complex, rather than predicted forces for the temporalis muscle. Our results demonstrate that relative sagittal crest height is poorly correlated with relative cranial bite force, suggesting high force application is not a driver for pronounced sagittal crests in this sample. The divergent biomechanical capabilities of different contemporaneous tapirids may have allowed multiple species to occupy overlapping territories and partition resources to avoid excess competition. Bite forces in tapirs peak in Pleistocene species, independent of body size, suggesting possible dietary shifts as a potential result of climatic changes during this epoch.
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Affiliation(s)
- Lisa VAN Linden
- Functional Morphology Lab, Department of Biology, Campus Drie Eiken, Universiteit Antwerpen, Antwerpen, Belgium
| | - Kim Stoops
- Functional Morphology Lab, Department of Biology, Campus Drie Eiken, Universiteit Antwerpen, Antwerpen, Belgium
| | - Larissa C C S Dumbá
- Departamento de Zoologia, Instituto de Ciências Biológicas, Universidade Federal de Minas Gerais, Minas Gerais, Brazil
| | - Mario A Cozzuol
- Departamento de Zoologia, Instituto de Ciências Biológicas, Universidade Federal de Minas Gerais, Minas Gerais, Brazil
| | - Jamie A Maclaren
- Functional Morphology Lab, Department of Biology, Campus Drie Eiken, Universiteit Antwerpen, Antwerpen, Belgium.,Evolution and Diversity Dynamics Lab, Department of Geology, Université de Liège, Quartier Agora, Liège, Belgium
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Gutarra S, Rahman IA. The locomotion of extinct secondarily aquatic tetrapods. Biol Rev Camb Philos Soc 2021; 97:67-98. [PMID: 34486794 DOI: 10.1111/brv.12790] [Citation(s) in RCA: 13] [Impact Index Per Article: 4.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/11/2021] [Revised: 08/14/2021] [Accepted: 08/18/2021] [Indexed: 02/06/2023]
Abstract
The colonisation of freshwater and marine ecosystems by land vertebrates has repeatedly occurred in amphibians, reptiles, birds and mammals over the course of 300 million years. Functional interpretations of the fossil record are crucial to understanding the forces shaping these evolutionary transitions. Secondarily aquatic tetrapods have acquired a suite of anatomical, physiological and behavioural adaptations to locomotion in water. However, much of this information is lost for extinct clades, with fossil evidence often restricted to osteological data and a few extraordinary specimens with soft tissue preservation. Traditionally, functional morphology in fossil secondarily aquatic tetrapods was investigated through comparative anatomy and correlation with living functional analogues. However, in the last two decades, biomechanics in palaeobiology has experienced a remarkable methodological shift. Anatomy-based approaches are increasingly rigorous, informed by quantitative techniques for analysing shape. Moreover, the incorporation of physics-based methods has enabled objective tests of functional hypotheses, revealing the importance of hydrodynamic forces as drivers of evolutionary innovation and adaptation. Here, we present an overview of the latest research on the locomotion of extinct secondarily aquatic tetrapods, with a focus on amniotes, highlighting the state-of-the-art experimental approaches used in this field. We discuss the suitability of these techniques for exploring different aspects of locomotory adaptation, analysing their advantages and limitations and laying out recommendations for their application, with the aim to inform future experimental strategies. Furthermore, we outline some unexplored research avenues that have been successfully deployed in other areas of palaeobiomechanical research, such as the use of dynamic models in feeding mechanics and terrestrial locomotion, thus providing a new methodological synthesis for the field of locomotory biomechanics in extinct secondarily aquatic vertebrates. Advances in imaging technology and three-dimensional modelling software, new developments in robotics, and increased availability and awareness of numerical methods like computational fluid dynamics make this an exciting time for analysing form and function in ancient vertebrates.
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Affiliation(s)
- Susana Gutarra
- School of Earth Sciences, University of Bristol, Life Sciences Building, 24 Tyndall Avenue, Bristol, BS8 1TQ, U.K.,Department of Earth Sciences, the Natural History Museum, Cromwell Road, London, U.K
| | - Imran A Rahman
- Department of Earth Sciences, the Natural History Museum, Cromwell Road, London, U.K.,Oxford University Museum of Natural History, Parks Road, Oxford, OX1 3PW, U.K
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Baskin J, Gervais PD, Gervais CJ. A Late Pleistocene capybara (Rodentia, Caviidae, Hydrochoerinae) from near Houston, Texas, USA, with a brief review of North American fossil capybaras. PROCEEDINGS OF THE ACADEMY OF NATURAL SCIENCES OF PHILADELPHIA 2020. [DOI: 10.1635/053.167.0105] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/11/2022]
Affiliation(s)
- Jon Baskin
- Department of Biological and Health Sciences, Texas A&M University-Kingsville, Kingsville, TX 78363 USA
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Barrón-Ortiz CI, Avilla LS, Jass CN, Bravo-Cuevas VM, Machado H, Mothé D. What Is Equus? Reconciling Taxonomy and Phylogenetic Analyses. Front Ecol Evol 2019. [DOI: 10.3389/fevo.2019.00343] [Citation(s) in RCA: 21] [Impact Index Per Article: 4.2] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/13/2022] Open
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MacLaren JA, Nauwelaerts S. Modern Tapirs as Morphofunctional Analogues for Locomotion in Endemic Eocene European Perissodactyls. J MAMM EVOL 2019. [DOI: 10.1007/s10914-019-09460-1] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/27/2022]
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Maclaren JA, Hulbert RC, Wallace SC, Nauwelaerts S. A morphometric analysis of the forelimb in the genus Tapirus (Perissodactyla: Tapiridae) reveals influences of habitat, phylogeny and size through time and across geographical space. Zool J Linn Soc 2018. [DOI: 10.1093/zoolinnean/zly019] [Citation(s) in RCA: 10] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/17/2022]
Affiliation(s)
- Jamie A Maclaren
- Department of Biology, Universiteit Antwerpen, Campus Drie Eiken, Universiteitsplein, Wilrijk, Antwerp,, Belgium
| | - Richard C Hulbert
- Florida Museum of Natural History, University of Florida, Dickinson Hall, Gainesville, Florida, FL, USA
| | - Steven C Wallace
- Don Sundquist Center of Excellence in Paleontology, Department of Geosciences, East Tennessee State University, Johnson City TN, USA
| | - Sandra Nauwelaerts
- Department of Biology, Universiteit Antwerpen, Campus Drie Eiken, Universiteitsplein, Wilrijk, Antwerp,, Belgium
- Centre for Research and Conservation, Koninklijke Maatschappij voor Dierkunde (KMDA), Koningin Astridplein, Antwerp, Belgium
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MacLaren JA, Nauwelaerts S. A three-dimensional morphometric analysis of upper forelimb morphology in the enigmatic tapir (Perissodactyla: Tapirus) hints at subtle variations in locomotor ecology. J Morphol 2016; 277:1469-1485. [PMID: 27519626 DOI: 10.1002/jmor.20588] [Citation(s) in RCA: 13] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/22/2016] [Revised: 07/08/2016] [Accepted: 07/25/2016] [Indexed: 11/07/2022]
Abstract
Forelimb morphology is an indicator for terrestrial locomotor ecology. The limb morphology of the enigmatic tapir (Perissodactyla: Tapirus) has often been compared to that of basal perissodactyls, despite the lack of quantitative studies comparing forelimb variation in modern tapirs. Here, we present a quantitative assessment of tapir upper forelimb osteology using three-dimensional geometric morphometrics to test whether the four modern tapir species are monomorphic in their forelimb skeleton. The shape of the upper forelimb bones across four species (T. indicus; T. bairdii; T. terrestris; T. pinchaque) was investigated. Bones were laser scanned to capture surface morphology and 3D landmark analysis was used to quantify shape. Discriminant function analyses were performed to reveal features which could be used for interspecific discrimination. Overall our results show that the appendicular skeleton contains notable interspecific differences. We demonstrate that upper forelimb bones can be used to discriminate between species (>91% accuracy), with the scapula proving the most diagnostic bone (100% accuracy). Features that most successfully discriminate between the four species include the placement of the cranial angle of the scapula, depth of the humeral condyle, and the caudal deflection of the olecranon. Previous studies comparing the limbs of T. indicus and T. terrestris are corroborated by our quantitative findings. Moreover, the mountain tapir T. pinchaque consistently exhibited the greatest divergence in morphology from the other three species. Despite previous studies describing tapirs as functionally mediportal in their locomotor style, we find osteological evidence suggesting a spectrum of locomotor adaptations in the tapirs. We conclude that modern tapir forelimbs are neither monomorphic nor are tapirs as conserved in their locomotor habits as previously described. J. Morphol. 277:1469-1485, 2016. © 2016 Wiley Periodicals, Inc.
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Affiliation(s)
- Jamie A MacLaren
- Department of Biology, Universiteit Antwerpen, Building D, Campus Drie Eiken, Universiteitsplein, Wilrijk, Antwerp, 2610, Belgium.
| | - Sandra Nauwelaerts
- Department of Biology, Universiteit Antwerpen, Building D, Campus Drie Eiken, Universiteitsplein, Wilrijk, Antwerp, 2610, Belgium
- Centre for Research and Conservation, Koninklijke Maatschappij Voor Dierkunde (KMDA), Koningin Astridplein 26, Antwerp, 2018, Belgium
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Ruiz-García M, Castellanos A, Bernal LA, Pinedo-Castro M, Kaston F, Shostell JM. Mitogenomics of the mountain tapir (Tapirus pinchaque, Tapiridae, Perissodactyla, Mammalia) in Colombia and Ecuador: Phylogeography and insights into the origin and systematics of the South American tapirs. Mamm Biol 2016. [DOI: 10.1016/j.mambio.2015.11.001] [Citation(s) in RCA: 8] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/22/2022]
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Voss RS, Helgen KM, Jansa SA. Extraordinary claims require extraordinary evidence: a comment on Cozzuol et al. (2013): Fig. 1. J Mammal 2014. [DOI: 10.1644/14-mamm-a-054] [Citation(s) in RCA: 20] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/17/2022] Open
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