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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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2
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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: 2] [Impact Index Per Article: 2.0] [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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3
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Bader C, Delapré A, Houssaye A. Shape variation in the limb long bones of modern elephants reveals adaptations to body mass and habitat. J Anat 2023; 242:806-830. [PMID: 36824051 PMCID: PMC10093169 DOI: 10.1111/joa.13827] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/29/2022] [Revised: 01/06/2023] [Accepted: 01/06/2023] [Indexed: 02/25/2023] Open
Abstract
During evolution, several vertebrate lineages have shown trends towards an increase in mass. Such a trend is associated with physiological and musculoskeletal changes necessary to carry and move an increasingly heavy body. Due to their prominent role in the support and movement of the body, limb long bones are highly affected by these shifts in body mass. Elephants are the heaviest living terrestrial mammals, displaying unique features allowing them to withstand their massive weight, such as the columnarity of their limbs, and as such are crucial to understand the evolution towards high body mass in land mammals. In this study, we investigate the shape variation of the six limb long bones among the modern elephants, Elephas maximus and Loxodonta africana, to understand the effect of body mass and habitat on the external anatomy of the bones. To do so, we use three-dimensional geometric morphometrics (GMMs) and qualitative comparisons to describe the shape variation, at both the intraspecific and interspecific levels. Our results reveal that the two species share similar negative ontogenetic allometric patterns (i.e. becoming stouter with increased length) in their humerus and femur, but not in the other bones: the proximal epiphyses of the stylopod bones develop considerably during growth, while the distal epiphyses, which are involved in load distribution in the elbow and knee joints, are already massive in juveniles. We attribute this pattern to a weight-bearing adaptation already present in young specimens. Among adults of the same species, bone robustness increases with body mass, so that heavier specimens display stouter bones allowing for a better mechanical load distribution. While this robustness variation is significant for the humerus only, all the other bones appear to follow the same pattern. This is particularly visible in the ulna and tibia, but less so in the femur, which suggests that the forelimb and hindlimb adapted differently to high body mass support. Robustness analyses, while significant for the humerus only, suggest more robust long bones in Asian elephants than in African savanna elephants. More specifically, GMMs and qualitative comparisons indicate that three bones are clearly distinct when comparing the two species: in E. maximus the humerus, the ulna and the tibia display enlarged areas of muscular insertions for muscles involved in joint and limb stabilization, as well as in limb rotation. These results suggest a higher limb compliance in Asian elephants, associated with a higher dexterity, which could be linked to their habitat and foraging habits.
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Affiliation(s)
- Camille Bader
- Département Adaptations du Vivant, UMR 7179, Mécanismes adaptatifs et Évolution (MECADEV) CNRS/Muséum national d'Histoire naturelle, Paris, France
| | - Arnaud Delapré
- UMR 7205, Institut de Systématique, Evolution, Biodiversité (ISYEB), Muséum national d'Histoire naturelle, CNRS, SU, EPHE, UA, Paris, France
| | - Alexandra Houssaye
- Département Adaptations du Vivant, UMR 7179, Mécanismes adaptatifs et Évolution (MECADEV) CNRS/Muséum national d'Histoire naturelle, Paris, France
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Chatar N, Boman R, Fallon Gaudichon V, MacLaren JA, Fischer V. ‘Fossils’: A new, fast and open‐source protocol to simulate muscle‐driven biomechanical loading of bone. Methods Ecol Evol 2023. [DOI: 10.1111/2041-210x.14051] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/04/2023]
Affiliation(s)
- Narimane Chatar
- Evolution & Diversity Dynamics lab, UR Geology Université de Liège Liège Belgium
| | - Romain Boman
- Department of Aerospace and Mechanical Engineering, Non‐Linear Computational Mechanics (MN2L) Research Group Université de Liège Liège Belgium
| | - Valentin Fallon Gaudichon
- Evolution & Diversity Dynamics lab, UR Geology Université de Liège Liège Belgium
- Institut des Sciences de l'Evolution de Montpellier (ISEM) Université de Poitiers‐Montpellier Montpellier France
| | - Jamie A. MacLaren
- Evolution & Diversity Dynamics lab, UR Geology Université de Liège Liège Belgium
- Functional Morphology Lab, Department of Biology Universiteit Antwerpen Antwerpen Belgium
| | - Valentin Fischer
- Evolution & Diversity Dynamics lab, UR Geology Université de Liège Liège Belgium
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5
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Inferring the palaeobiology of palorchestid marsupials through analysis of mammalian humeral and femoral shape. J MAMM EVOL 2022. [DOI: 10.1007/s10914-022-09640-6] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/24/2022]
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6
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Holmes J, Sustaita D, Hertel F. Geometric Morphometric Analysis of the Humerus in New and Old World Vultures. J Morphol 2022; 283:379-394. [PMID: 35038183 DOI: 10.1002/jmor.21449] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/22/2020] [Revised: 12/30/2021] [Accepted: 01/12/2022] [Indexed: 11/08/2022]
Abstract
The vulture guild is composed of two distinct groups, Old and New World, that provide a unique insight into how morphology varies among convergent species. All vultures are considered to be large birds of prey that utilize a style of flight called thermal soaring to search and feed primarily on carrion. Even though this flight style is exhibited among all 23 species, slight variations in their skeletal morphology may relate to their differences in ecology. We hypothesized that vulture humeral morphology varies in relation to these organisms' habitat, average body mass, courtship displays, and migratory behavior. To address this hypothesis, we used three-dimensional geometric morphometrics to measure the overall shape differences of vulture humeri. Humeral morphology was found to vary most by habitat association and migratory tendency. The humeri of vultures that inhabit forested areas exhibit features that suggest increased flapping flight compared to those in open and mountainous regions. Migratory species were found to possess more robust features near the glenohumeral joint. We found these (and other features) have some utility for predicting ecology and behavior, but we suggest that further investigation into skeletal and muscular wing elements may reveal greater understanding of the habits of extinct vulture species. This article is protected by copyright. All rights reserved.
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Affiliation(s)
- Jacob Holmes
- Department of Biology, California State University, Northridge, Northridge, California
| | - Diego Sustaita
- Department of Biological Sciences, California State University, San Marcos, San Marcos, California
| | - Fritz Hertel
- Department of Biology, California State University, Northridge, Northridge, California
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Houssaye A, de Perthuis A, Houée G. Sesamoid bones also show functional adaptation in their microanatomy-The example of the patella in Perissodactyla. J Anat 2022; 240:50-65. [PMID: 34402049 PMCID: PMC8655183 DOI: 10.1111/joa.13530] [Citation(s) in RCA: 2] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/05/2021] [Revised: 07/21/2021] [Accepted: 07/21/2021] [Indexed: 11/27/2022] Open
Abstract
The patella is the largest sesamoid bone of the skeleton. It is strongly involved in the knee, improving output force and velocity of the knee extensors, and thus plays a major role in locomotion and limb stability. However, the relationships between its structure and functional constraints, that would enable a better understanding of limb bone functional adaptations, are poorly known. This contribution proposes a comparative analysis, both qualitative and quantitative, of the microanatomy of the whole patella in perissodactyls, which show a wide range of morphologies, masses, and locomotor abilities, in order to investigate how the microanatomy of the patella adapts to evolutionary constraints. The inner structure of the patella consists of a spongiosa surrounded by a compact cortex. Contrary to our expectations, there is no increase in compactness with bone size, and thus body size and weight, but only an increase in the tightness of the spongiosa. No particular thickening of the cortex associated with muscle insertions is noticed but a strong thickening is observed anteriorly at about mid-length, where the strong intermediate patellar ligament inserts. The trabeculae are mainly oriented perpendicularly to the posterior articular surface, which highlights that the main stress is anteroposteriorly directed, maintaining the patella against the femoral trochlea. Conversely, anteriorly, trabeculae are rather circumferentially oriented, following the insertion of the patellar ligament and, possibly also, of the quadriceps tendon. A strong variation is observed among perissodactyl families but also intraspecifically, which is in accordance with previous studies suggesting a higher variability in sesamoid bones. Clear trends are nevertheless observed between the three families. Equids have a much thinner cortex than ceratomorphs. Rhinos and equids, both characterized by a development of the medial border, show an increase in trabecular density laterally suggesting stronger stresses laterally. The inner structure in tapirs is more homogeneous despite the absence of medial development of the medial border with no "compensation" of the inner structure, which suggests different stresses on their knees associated with a different morphology of their patellofemoral joint.
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Affiliation(s)
- Alexandra Houssaye
- Département Adaptations du vivantUMR 7179 CNRS/Muséum National d'Histoire NaturelleParisFrance
| | - Adrien de Perthuis
- Département Adaptations du vivantUMR 7179 CNRS/Muséum National d'Histoire NaturelleParisFrance
| | - Guillaume Houée
- Département Adaptations du vivantUMR 7179 CNRS/Muséum National d'Histoire NaturelleParisFrance
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8
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Mielke F, Van Ginneken C, Aerts P. Quantifying intralimb coordination of terrestrial ungulates with Fourier coefficient affine superimposition. Zool J Linn Soc 2019. [DOI: 10.1093/zoolinnean/zlz135] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/14/2022]
Abstract
Abstract
Many phenomena related to motor behaviour in animals are spatially and temporally periodic, making them accessible for transformation to the frequency domain via Fourier Series. Although this has been applied previously, it had not been noticed that the characteristic arrangement of Fourier coefficients in their complex-valued representation resembles landmarks in geometric morphometrics. We define a superimposition procedure in the frequency domain, which removes affine differences (mean, amplitude, phase) to reveal and compare the shape of periodic kinematic measures. This procedure is conceptually linked to dynamic similarity, which can thereby be assessed on the level of individual limb elements. We demonstrate how to make intralimb coordination accessible for large-scale, quantitative analyses. By applying this to a dataset from terrestrial ungulates, dominant patterns in forelimb coordination during walking are identified. This analysis shows that typical strides of these animals differ mostly in how much the limbs are lifted in the presence or absence of obstructive substrate features. This is shown to be independent of morphological features. Besides revealing fundamental characteristics of ungulate locomotion, we argue that the suggested method is generally suitable for the large-scale quantitative assessment of coordination and dynamics in periodic locomotor phenomena.
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Affiliation(s)
- Falk Mielke
- Laboratory of Applied Veterinary Morphology, Department of Veterinary Sciences, Faculty of Biomedical, Pharmaceutical and Veterinary Sciences, University of Antwerp, Wilrijk, Belgium
- Laboratory of Functional Morphology, Department of Biology, Faculty of Sciences, University of Antwerp, Wilrijk, Belgium
| | - Chris Van Ginneken
- Laboratory of Applied Veterinary Morphology, Department of Veterinary Sciences, Faculty of Biomedical, Pharmaceutical and Veterinary Sciences, University of Antwerp, Wilrijk, Belgium
| | - Peter Aerts
- Laboratory of Functional Morphology, Department of Biology, Faculty of Sciences, University of Antwerp, Wilrijk, Belgium
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9
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Mallet C, Cornette R, Billet G, Houssaye A. Interspecific variation in the limb long bones among modern rhinoceroses-extent and drivers. PeerJ 2019; 7:e7647. [PMID: 31579585 PMCID: PMC6766374 DOI: 10.7717/peerj.7647] [Citation(s) in RCA: 18] [Impact Index Per Article: 3.6] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/23/2019] [Accepted: 08/08/2019] [Indexed: 11/20/2022] Open
Abstract
Among amniotes, numerous lineages are subject to an evolutionary trend toward body mass and size increases. Large terrestrial species may face important constraints linked to weight bearing, and the limb segments are particularly affected by such constraints due to their role in body support and locomotion. Such groups showing important limb modifications related to high body mass have been called “graviportal.” Often considered graviportal, rhinoceroses are among the heaviest terrestrial mammals and are thus of particular interest to understand the limb modifications related to body mass and size increase. Here, we present a morphofunctional study of the shape variation of the limb long bones among the five living rhinos to understand how the shape may vary between these species in relation with body size, body mass and phylogeny. We used three dimensional geometric morphometrics and comparative analyses to quantify the shape variation. Our results indicate that the five species display important morphological differences depending on the considered bones. The humerus and the femur exhibit noticeable interspecific differences between African and Asiatic rhinos, associated with a significant effect of body mass. The radius and ulna are more strongly correlated with body mass. While the tibia exhibits shape variation both linked with phylogeny and body mass, the fibula displays the greatest intraspecific variation. We highlight three distinct morphotypes of bone shape, which appear in accordance with the phylogeny. The influence of body mass also appears unequally expressed on the different bones. Body mass increase among the five extant species is marked by an increase of the general robustness, more pronounced attachments for muscles and a development of medial parts of the bones. Our study underlines that the morphological features linked to body mass increase are not similar between rhinos and other heavy mammals such as elephants and hippos, suggesting that the weight bearing constraint can lead to different morphological responses.
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Affiliation(s)
- Christophe Mallet
- Mécanismes adaptatifs et évolution (MECADEV), UMR 7179, MNHN, CNRS, Muséum National d'Histoire Naturelle, Paris, France
| | - Raphaël Cornette
- Institut de Systématique, Evolution, Biodiversité (ISYEB), UMR 7205, MNHN, CNRS, SU, EPHE, UA, Muséum National d'Histoire Naturelle, Paris, France
| | - Guillaume Billet
- Centre de Recherche en Paléontologie-Paris (CR2P), UMR CNRS 7207, MNHN, CNRS, SU, Muséum National d'Histoire Naturelle, Paris, France
| | - Alexandra Houssaye
- Mécanismes adaptatifs et évolution (MECADEV), UMR 7179, MNHN, CNRS, Muséum National d'Histoire Naturelle, Paris, France
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10
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MacLaren JA, McHorse BK. Comparative forelimb myology and muscular architecture of a juvenile Malayan tapir (Tapirus indicus). J Anat 2019; 236:85-97. [PMID: 31515803 DOI: 10.1111/joa.13087] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Accepted: 08/13/2019] [Indexed: 12/21/2022] Open
Abstract
The absence of preserved soft tissues in the fossil record is frequently a hindrance for palaeontologists wishing to investigate morphological shifts in key skeletal systems, such as the limbs. Understanding the soft tissue composition of modern species can aid in understanding changes in musculoskeletal features through evolution, including those pertaining to locomotion. Establishing anatomical differences in soft tissues utilising an extant phylogenetic bracket can, in turn, assist in interpreting morphological changes in hard tissues and modelling musculoskeletal movements during evolutionary transitions (e.g. digit reduction in perissodactyls). Perissodactyls (horses, rhinoceroses, tapirs and their relatives) are known to have originated with a four-toed (tetradactyl) forelimb condition. Equids proceeded to reduce all but their central digit, resulting in monodactyly, whereas tapirs retained the ancestral tetradactyl state. The modern Malayan tapir (Tapirus indicus) has been shown to exhibit fully functional tetradactyly in its forelimb, more so than any other tapir, and represents an ideal case-study for muscular arrangement and architectural comparison with the highly derived monodactyl Equus. Here, we present the first quantification of muscular architecture of a tetradactyl perissodactyl (T. indicus), and compare it to measurements from modern monodactyl caballine horse (Equus ferus caballus). Each muscle of the tapir forelimb was dissected out from a cadaver and measured for architectural properties: muscle-tendon unit (MTU) length, MTU mass, muscle mass, pennation angle, and resting fibre length. Comparative parameters [physiological cross-sectional area (PCSA), muscle volume, and % muscle mass] were then calculated from the raw measurements. In the shoulder region, the infraspinatus of T. indicus exhibits dual origination sites on either side of the deflected scapular spine. Within ungulates, this condition has only been previously reported in suids. Differences in relative contribution to limb muscle mass between T. indicus and Equus highlight forelimb muscles that affect mobility in the lateral and medial digits (e.g. extensor digitorum lateralis). These muscles were likely reduced in equids during their evolutionary transition from tetradactyl forest-dwellers to monodactyl, open-habitat specialists. Patterns of PCSA across the forelimb were similar between T. indicus and Equus, with the notable exceptions of the biceps brachii and flexor carpi ulnaris, which were much larger in Equus. The differences observed in PCSA between the tapir and horse forelimb muscles highlight muscles that are essential for maintaining stability in the monodactyl limb while moving at high speeds. This quantitative dataset of muscle architecture in a functionally tetradactyl perissodactyl is a pivotal first step towards reconstructing the locomotor capabilities of extinct, four-toed ancestors of modern perissodactyls, and providing further insights into the equid locomotor transition.
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Affiliation(s)
- Jamie A MacLaren
- Functional Morphology Lab, Department of Biology, Universiteit Antwerpen, Antwerp, Belgium.,Evolution and Diversity Dynamics Lab, Department of Geology, Université Liège, Liège, Belgium
| | - Brianna K McHorse
- Museum of Comparative Zoology, Cambridge, MA, USA.,Department of Organismic and Evolutionary Biology, Harvard University, Cambridge, MA, USA.,Concord Field Station, Department of Organismic and Evolutionary Biology, Harvard University, Bedford, MA, USA
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11
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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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12
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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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13
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McHorse BK, Biewener AA, Pierce SE. Mechanics of evolutionary digit reduction in fossil horses (Equidae). Proc Biol Sci 2018; 284:rspb.2017.1174. [PMID: 28835559 DOI: 10.1098/rspb.2017.1174] [Citation(s) in RCA: 24] [Impact Index Per Article: 4.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/26/2017] [Accepted: 07/12/2017] [Indexed: 01/15/2023] Open
Abstract
Digit reduction is a major trend that characterizes horse evolution, but its causes and consequences have rarely been quantitatively tested. Using beam analysis on fossilized centre metapodials, we tested how locomotor bone stresses changed with digit reduction and increasing body size across the horse lineage. Internal bone geometry was captured from 13 fossil horse genera that covered the breadth of the equid phylogeny and the spectrum of digit reduction and body sizes, from Hyracotherium to Equus To account for the load-bearing role of side digits, a novel, continuous measure of digit reduction was also established-toe reduction index (TRI). Our results show that without accounting for side digits, three-toed horses as late as Parahippus would have experienced physiologically untenable bone stresses. Conversely, when side digits are modelled as load-bearing, species at the base of the horse radiation through Equus probably maintained a similar safety factor to fracture stress. We conclude that the centre metapodial compensated for evolutionary digit reduction and body mass increases by becoming more resistant to bending through substantial positive allometry in internal geometry. These results lend support to two historical hypotheses: that increasing body mass selected for a single, robust metapodial rather than several smaller ones; and that, as horse limbs became elongated, the cost of inertia from the side toes outweighed their utility for stabilization or load-bearing.
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Affiliation(s)
- Brianna K McHorse
- Museum of Comparative Zoology and Department of Organismic and Evolutionary Biology, Harvard University, Cambridge, MA 02138, USA .,Concord Field Station, Department of Organismic and Evolutionary Biology, Harvard University, Bedford, MA 01730, USA
| | - Andrew A Biewener
- Concord Field Station, Department of Organismic and Evolutionary Biology, Harvard University, Bedford, MA 01730, USA
| | - Stephanie E Pierce
- Museum of Comparative Zoology and Department of Organismic and Evolutionary Biology, Harvard University, Cambridge, MA 02138, USA
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14
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MacLaren JA, Nauwelaerts S. Interspecific variation in the tetradactyl manus of modern tapirs (Perissodactyla: Tapirus
) exposed using geometric morphometrics. J Morphol 2017; 278:1517-1535. [DOI: 10.1002/jmor.20728] [Citation(s) in RCA: 6] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/22/2017] [Revised: 05/26/2017] [Accepted: 06/23/2017] [Indexed: 11/06/2022]
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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