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Jones KE, Angielczyk KD, Pierce SE. Origins of mammalian vertebral function revealed through digital bending experiments. Proc Biol Sci 2024; 291:20240820. [PMID: 38981526 DOI: 10.1098/rspb.2024.0820] [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: 04/08/2024] [Accepted: 06/13/2024] [Indexed: 07/11/2024] Open
Abstract
Unravelling the functional steps that underlie major transitions in the fossil record is a significant challenge for biologists owing to the difficulties of interpreting functional capabilities of extinct organisms. New computational modelling approaches provide exciting avenues for testing function in the fossil record. Here, we conduct digital bending experiments to reconstruct vertebral function in non-mammalian synapsids, the extinct forerunners of mammals, to provide insights into the functional underpinnings of the synapsid-mammal transition. We estimate range of motion and stiffness of intervertebral joints in eight non-mammalian synapsid species alongside a comparative sample of extant tetrapods, including salamanders, reptiles and mammals. We show that several key aspects of mammalian vertebral function evolved outside crown Mammalia. Compared to early diverging non-mammalian synapsids, cynodonts stabilized the posterior trunk against lateroflexion, while evolving axial rotation in the anterior trunk. This was later accompanied by posterior sagittal bending in crown mammals, and perhaps even therians specifically. Our data also support the prior hypothesis that functional diversification of the mammalian trunk occurred via co-option of existing morphological regions in response to changing selective demands. Thus, multiple functional and evolutionary steps underlie the origin of remarkable complexity in the mammalian backbone.
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Affiliation(s)
- Katrina E Jones
- Museum of Comparative Zoology and Department of Organismic and Evolutionary Biology, Harvard University, 26 Oxford Street , Cambridge, MA 02138, USA
- Department of Earth and Environmental Sciences, University of Manchester, Williamson Building, Oxford Road , Manchester M13 9PL, UK
| | - Kenneth D Angielczyk
- Negaunee Integrative Research Center, Field Museum of Natural History, 1400 South Lake Shore Drive , Chicago, IL 60605-2496, USA
| | - Stephanie E Pierce
- Museum of Comparative Zoology and Department of Organismic and Evolutionary Biology, Harvard University, 26 Oxford Street , Cambridge, MA 02138, USA
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Kinoshita Y, Hirasaki E. Variation of thoracolumbar vertebral morphology in anthropoid primates. AMERICAN JOURNAL OF BIOLOGICAL ANTHROPOLOGY 2024; 184:e24904. [PMID: 38305568 DOI: 10.1002/ajpa.24904] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Received: 03/03/2023] [Revised: 11/29/2023] [Accepted: 01/13/2024] [Indexed: 02/03/2024]
Abstract
OBJECTIVES Morphological variation among extant primates in the lumbar vertebral column is well studied. However, knowledge concerning the thoracic spine, an important region responsible for supporting and facilitating movement in the upper trunk, remains relatively scarce. Consequently, our comprehension of the functional differentiation exhibited throughout the thoracolumbar vertebral column among various primate species remains constrained. In this study, we examined patterns of morphological variation in the thoracolumbar vertebral column of extant hominoids, cercopithecoids, and Ateles. MATERIALS AND METHODS We collected external shape data on 606 thoracic and lumbar vertebrae from Homo sapiens, Pan troglodytes, Hylobates lar, Macaca fuscata, Chlorocebus aethiops, Colobus guereza, Ateles geoffroyi, and A. belzebuth. Forty-four landmarks were obtained on the three-dimensional surface. Geometric morphometrics was used to quantify the centroid size and variation of the shapes of thoracic and lumbar vertebrae. RESULTS Cercopithecoids exhibited greater variation in the size and shape of their thoracic and lumbar vertebrae compared to hominoids and Ateles. Although many vertebral features contributed to the observed variation throughout the thoracolumbar vertebral column within the taxon, the transverse and spinous processes exhibited relatively major contributions. DISCUSSION Our results suggest that quadrupedal locomotion requires the functional differentiation between thoracic and lumbar vertebrae, and for hominoids, functional adaptation to orthograde posture necessitates a relatively more uniform shape of thoracic and lumbar vertebrae.
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Affiliation(s)
- Yuki Kinoshita
- Center for the Evolutionary Origins of Human Behavior, Kyoto University, Inuyama, Japan
| | - Eishi Hirasaki
- Center for the Evolutionary Origins of Human Behavior, Kyoto University, Inuyama, Japan
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3
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Kinoshita Y, Hirasaki E. Range of rotation of thoracolumbar vertebrae in Japanese macaques. Anat Rec (Hoboken) 2024; 307:223-232. [PMID: 37289013 DOI: 10.1002/ar.25273] [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: 02/16/2023] [Revised: 05/25/2023] [Accepted: 05/25/2023] [Indexed: 06/09/2023]
Abstract
In humans, the range of thoracic vertebral rotation is known to be greater than that of the lumbar vertebrae due to their zygapophyseal orientation and soft tissue structure. However, little is known regarding vertebral movements in non-human primate species, which are primarily quadrupedal walkers. To understand the evolutionary background of human vertebral movements, this study estimated the range of axial rotation of the thoracolumbar spine in macaque monkeys. First, computed tomography (CT) was performed while passively rotating the trunk of whole-body cadavers of Japanese macaques, after which the motion of each thoracolumbar vertebra was estimated. Second, to evaluate the influence of the shoulder girdle and surrounding soft tissues, specimens with only bones and ligaments were prepared, after which the rotation of each vertebra was estimated using an optical motion tracking system. In both conditions, the three-dimensional coordinates of each vertebra were digitized, and the axial rotational angles between adjacent vertebrae were calculated. In the whole-body condition, the lower thoracic vertebrae had a greater range of rotation than did the other regions, similar to that observed in humans. In addition, absolute values for the range of rotation were similar between humans and macaques. However, in the bone-ligament preparation condition, the upper thoracic vertebrae had a range of rotation similar to that of the lower thoracic vertebrae. Contrary to previous speculations, our results showed that the mechanical restrictions by the ribs were not as significant; rather, the shoulder girdle largely restricted the rotation of the upper thoracic vertebrae, at least, in macaques.
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Affiliation(s)
- Yuki Kinoshita
- Center for the Evolutionary Origins of Human Behavior, Kyoto University, Inuyama, Aichi, Japan
| | - Eishi Hirasaki
- Center for the Evolutionary Origins of Human Behavior, Kyoto University, Inuyama, Aichi, Japan
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4
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Adler KA, De Nault DL, Cardoza CM, Womack M. Evolutionary rates and shape variation along the anuran vertebral column with attention to phylogeny, body size, and ecology. Evolution 2022; 76:2724-2738. [PMID: 36117276 DOI: 10.1111/evo.14614] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/03/2022] [Revised: 07/31/2022] [Accepted: 08/08/2022] [Indexed: 01/22/2023]
Abstract
The vertebral column is critical to a vertebrate species' flexibility and skeletal support, making vertebrae a clear target for selection. Anurans (frogs and toads) have a unique, truncated vertebral column that appears constrained to provide axial rigidity for efficient jumping. However, no study has examined how presacral vertebrae shape varies among anuran species at the macroevolutionary scale nor how intrinsic (developmental and phylogenetic) and extrinsic (ecological) factors may have influenced vertebrae shape evolution. We used microCT scans and phylogenetic comparative methods to examine the vertebrae of hundreds of anuran species that vary in body size as well as adult and larval ecology. We found variation in shape and evolutionary rates among anuran vertebrae, dispelling any notion that trunk vertebrae evolve uniformly. We discovered the highest evolutionary rates in the cervical vertebrae and in the more caudal trunk vertebrae. We found little evidence for selection pressures related to adult or larval ecology affecting vertebrae evolution, but we did find body size was highly associated with vertebrae shape and microhabitat (mainly burrowing) affected those allometric relationships. Our results provide an interesting comparison to vertebrae evolution in other clades and a jumping-off point for studies of anuran vertebrae evolution and development.
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Affiliation(s)
- Katie A Adler
- Museum of Vertebrate Zoology, University of California, Berkeley, Berkeley, California, 94720
| | - Diego L De Nault
- Museum of Vertebrate Zoology, University of California, Berkeley, Berkeley, California, 94720
| | - Cassandra M Cardoza
- Museum of Vertebrate Zoology, University of California, Berkeley, Berkeley, California, 94720
| | - Molly Womack
- Museum of Vertebrate Zoology, University of California, Berkeley, Berkeley, California, 94720.,Department of Biology, Utah State University, Logan, Utah, 84322
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Boynton AM, Carrier DR. The human neck is part of the musculoskeletal core: cervical muscles help stabilize the pelvis during running and jumping. Integr Org Biol 2022; 4:obac021. [PMID: 35854827 PMCID: PMC9280985 DOI: 10.1093/iob/obac021] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/21/2022] Open
Abstract
During locomotion, cervical muscles must be active to stabilize the head as the body accelerates and decelerates. We hypothesized that cervical muscles are also part of the linked chain of axial muscles that provide core stabilization against torques applied to the hip joint by the extrinsic muscles of the legs. To test whether specific cervical muscles play a role in postural stabilization of the head and/or core stabilization of the pelvic girdle, we used surface electromyography to measure changes in muscle activity in response to force manipulations during constant speed running and maximum effort counter-movement jumps. We found that doubling the mass of the head during both running and maximum effort jumping had little or no effect on (1) acceleration of the body and (2) cervical muscle activity. Application of horizontal forward and rearward directed forces at the pelvis during running tripled mean fore and aft accelerations, thereby increasing both the pitching moments on the head and flexion and extension torques applied to the hip. These manipulations primarily resulted in increases in cervical muscle activity that is appropriate for core stabilization of the pelvis. Additionally, when subjects jumped maximally with an applied downward directed force that reduced acceleration and therefore need for cervical muscles to stabilize the head, cervical muscle activity did not decrease. These results suggest that during locomotion, rather than acting to stabilize the head against the effects of inertia, the superficial muscles of the neck monitored in this study help to stabilize the pelvis against torques imposed by the extrinsic muscles of the legs at the hip joint. We suggest that a division of labor may exist between deep cervical muscles that presumably provide postural stabilization of the head versus superficial cervical muscles that provide core stabilization against torques applied to the pelvic and pectoral girdles by the extrinsic appendicular muscles.
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Affiliation(s)
- Alicia M Boynton
- Division of Biological Science, University of Utah , Salt Lake City, Utah, 84112, USA
| | - David R Carrier
- Division of Biological Science, University of Utah , Salt Lake City, Utah, 84112, USA
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Oliver JD, Jones KE, Pierce SE, Hautier L. Size and shape regional differentiation during the development of the spine in the nine-banded armadillo (Dasypus novemcinctus). Evol Dev 2021; 23:496-512. [PMID: 34813149 DOI: 10.1111/ede.12393] [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: 03/17/2021] [Revised: 10/27/2021] [Accepted: 10/29/2021] [Indexed: 11/28/2022]
Abstract
Xenarthrans (armadillos, anteaters, sloths, and their extinct relatives) are unique among mammals in displaying a distinctive specialization of the posterior trunk vertebrae-supernumerary vertebral xenarthrous articulations. This study seeks to understand how xenarthry develops through ontogeny and if it may be constrained to appear within pre-existing vertebral regions. Using three-dimensional geometric morphometrics on the neural arches of vertebrae, we explore phenotypic, allometric, and disparity patterns of the different axial morphotypes during the ontogeny of nine-banded armadillos. Shape-based regionalization analyses showed that the adult thoracolumbar column is divided into three regions according to the presence or absence of ribs and the presence or absence of xenarthrous articulations. A three-region division was retrieved in almost all specimens through development, although younger stages (e.g., fetuses, neonates) have more region boundary variability. In size-based regionalization analyses, thoracolumbar vertebrae are separated into two regions: a prediaphragmatic, prexenarthrous region, and a postdiaphragmatic xenarthrous region. We show that posterior thoracic vertebrae grow at a slower rate, while anterior thoracics and lumbars grow at a faster rate relatively, with rates decreasing anteroposteriorly in the former and increasing anteroposteriorly in the latter. We propose that different proportions between vertebrae and vertebral regions might result from differences in growth pattern and timing of ossification.
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Affiliation(s)
- Jillian D Oliver
- Department of Organismic and Evolutionary Biology, Museum of Comparative Zoology, Harvard University, Cambridge, Massachusetts, USA
| | - Katrina E Jones
- Department of Organismic and Evolutionary Biology, Museum of Comparative Zoology, Harvard University, Cambridge, Massachusetts, USA
| | - Stephanie E Pierce
- Department of Organismic and Evolutionary Biology, Museum of Comparative Zoology, Harvard University, Cambridge, Massachusetts, USA
| | - Lionel Hautier
- Institut des Sciences de l'Évolution, Université Montpellier, CNRS, IRD, EPHE, Montpellier, France
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Jones KE, Brocklehurst RJ, Pierce SE. AutoBend: An Automated Approach for Estimating Intervertebral Joint Function from Bone-Only Digital Models. Integr Org Biol 2021; 3:obab026. [PMID: 34661062 PMCID: PMC8514422 DOI: 10.1093/iob/obab026] [Citation(s) in RCA: 3] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/20/2021] [Revised: 08/06/2021] [Accepted: 09/08/2021] [Indexed: 11/16/2022] Open
Abstract
Deciphering the biological function of rare or extinct species is key to understanding evolutionary patterns across the tree of life. While soft tissues are vital determinants of joint function, they are rarely available for study. Therefore, extracting functional signals from skeletons, which are more widely available via museum collections, has become a priority for the field of comparative biomechanics. While most work has focused on the limb skeleton, the axial skeleton plays a critical role in body support, respiration, and locomotion, and is therefore of central importance for understanding broad-scale functional evolution. Here, we describe and experimentally validate AutoBend, an automated approach to estimating intervertebral joint function from bony vertebral columns. AutoBend calculates osteological range of motion (oROM) by automatically manipulating digitally articulated vertebrae while incorporating multiple constraints on motion, including both bony intersection and the role of soft tissues by restricting excessive strain in both centrum and zygapophyseal articulations. Using AutoBend and biomechanical data from cadaveric experiments on cats and tegus, we validate important modeling parameters required for oROM estimation, including the degree of zygapophyseal disarticulation, and the location of the center of rotation. Based on our validation, we apply a model with the center of rotation located within the vertebral disk, no joint translation, around 50% strain permitted in both zygapophyses and disks, and a small amount of vertebral intersection permitted. Our approach successfully reconstructs magnitudes and craniocaudal patterns of motion obtained from ex vivo experiments, supporting its potential utility. It also performs better than more typical methods that rely solely on bony intersection, emphasizing the importance of accounting for soft tissues. We estimated the sensitivity of the analyses to vertebral model construction by varying joint spacing, degree of overlap, and the impact of landmark placement. The effect of these factors was small relative to biological variation craniocaudally and between bending directions. We also present a new approach for estimating joint stiffness directly from oROM and morphometric measurements that can successfully reconstruct the craniocaudal patterns, but not magnitudes, derived from experimental data. Together, this work represents a significant step forward for understanding vertebral function in difficult-to-study (e.g., rare or extinct) species, paving the way for a broader understanding of patterns of functional evolution in the axial skeleton.
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Affiliation(s)
- K E Jones
- Museum of Comparative Zoology and Department of Organismic and Evolutionary Biology, Harvard University, 26 Oxford Street, Cambridge, MA 02138, USA
| | - R J Brocklehurst
- Museum of Comparative Zoology and Department of Organismic and Evolutionary Biology, Harvard University, 26 Oxford Street, Cambridge, MA 02138, USA
| | - S E Pierce
- Museum of Comparative Zoology and Department of Organismic and Evolutionary Biology, Harvard University, 26 Oxford Street, Cambridge, MA 02138, USA
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Rose KAR, Tickle PG, Elsey RM, Sellers WI, Crossley DA, Codd JR. Scaling of axial muscle architecture in juvenile Alligator mississippiensis reveals an enhanced performance capacity of accessory breathing mechanisms. J Anat 2021; 239:1273-1286. [PMID: 34302302 PMCID: PMC8602021 DOI: 10.1111/joa.13523] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Key Words] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/16/2020] [Revised: 07/08/2021] [Accepted: 07/12/2021] [Indexed: 11/30/2022] Open
Abstract
Quantitative functional anatomy of amniote thoracic and abdominal regions is crucial to understanding constraints on and adaptations for facilitating simultaneous breathing and locomotion. Crocodilians have diverse locomotor modes and variable breathing mechanics facilitated by basal and derived (accessory) muscles. However, the inherent flexibility of these systems is not well studied, and the functional specialisation of the crocodilian trunk is yet to be investigated. Increases in body size and trunk stiffness would be expected to cause a disproportionate increase in muscle force demands and therefore constrain the basal costal aspiration mechanism, necessitating changes in respiratory mechanics. Here, we describe the anatomy of the trunk muscles, their properties that determine muscle performance (mass, length and physiological cross‐sectional area [PCSA]) and investigate their scaling in juvenile Alligator mississippiensis spanning an order of magnitude in body mass (359 g–5.5 kg). Comparatively, the expiratory muscles (transversus abdominis, rectus abdominis, iliocostalis), which compress the trunk, have greater relative PCSA being specialised for greater force‐generating capacity, while the inspiratory muscles (diaphragmaticus, truncocaudalis ischiotruncus, ischiopubis), which create negative internal pressure, have greater relative fascicle lengths, being adapted for greater working range and contraction velocity. Fascicle lengths of the accessory diaphragmaticus scaled with positive allometry in the alligators examined, enhancing contractile capacity, in line with this muscle's ability to modulate both tidal volume and breathing frequency in response to energetic demand during terrestrial locomotion. The iliocostalis, an accessory expiratory muscle, also demonstrated positive allometry in fascicle lengths and mass. All accessory muscles of the infrapubic abdominal wall demonstrated positive allometry in PCSA, which would enhance their force‐generating capacity. Conversely, the basal tetrapod expiratory pump (transversus abdominis) scaled isometrically, which may indicate a decreased reliance on this muscle with ontogeny. Collectively, these findings would support existing anecdotal evidence that crocodilians shift their breathing mechanics as they increase in size. Furthermore, the functional specialisation of the diaphragmaticus and compliance of the body wall in the lumbar region against which it works may contribute to low‐cost breathing in crocodilians.
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Affiliation(s)
- Kayleigh A R Rose
- Department of Biosciences, College of Science, Swansea University, Wales, UK
| | - Peter G Tickle
- School of Biomedical Sciences, Faculty of Biological Sciences, University of Leeds, Leeds, UK
| | - Ruth M Elsey
- Louisiana Department of Wildlife and Fisheries, Rockefeller Wildlife Refuge, Grand Chenier, LA, USA
| | - William I Sellers
- Department of Earth and Environmental Sciences, Faculty of Science and Engineering, University of Manchester, Manchester, UK
| | - Dane A Crossley
- Department of Biological Sciences, University of North Texas, Denton, TX, USA
| | - Jonathan R Codd
- Faculty of Biology, Medicine and Health, University of Manchester, Manchester, UK
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Carter AM, Hsieh ST, Dodson P, Sallan L. Early amphibians evolved distinct vertebrae for habitat invasions. PLoS One 2021; 16:e0251983. [PMID: 34106947 PMCID: PMC8189462 DOI: 10.1371/journal.pone.0251983] [Citation(s) in RCA: 4] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/07/2020] [Accepted: 05/06/2021] [Indexed: 11/19/2022] Open
Abstract
Living tetrapods owe their existence to a critical moment 360-340 million years ago when their ancestors walked on land. Vertebrae are central to locomotion, yet systematic testing of correlations between vertebral form and terrestriality and subsequent reinvasions of aquatic habitats is lacking, obscuring our understanding of movement capabilities in early tetrapods. Here, we quantified vertebral shape across a diverse group of Paleozoic amphibians (Temnospondyli) encompassing different habitats and nearly the full range of early tetrapod vertebral shapes. We demonstrate that temnospondyls were likely ancestrally terrestrial and had several early reinvasions of aquatic habitats. We find a greater diversity in temnospondyl vertebrae than previously known. We also overturn long-held hypotheses centered on weight-bearing, showing that neural arch features, including muscle attachment, were plastic across the water-land divide and do not provide a clear signal of habitat preferences. In contrast, intercentra traits were critical, with temnospondyls repeatedly converging on distinct forms in terrestrial and aquatic taxa, with little overlap between. Through our geometric morphometric study, we have been able to document associations between vertebral shape and environmental preferences in Paleozoic tetrapods and to reveal morphological constraints imposed by vertebrae to locomotion, independent of ancestry.
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Affiliation(s)
- Aja Mia Carter
- Department of Earth and Environmental Sciences, University of Pennsylvania, Philadelphia, PA, United States of America
- * E-mail:
| | - S. Tonia Hsieh
- Department of Biology, Temple University, Philadelphia, PA, United States of America
| | - Peter Dodson
- Department of Earth and Environmental Sciences, University of Pennsylvania, Philadelphia, PA, United States of America
- Department of Biomedical Sciences, School of Veterinary Medicine, University of Pennsylvania, Philadelphia, PA, United States of America
| | - Lauren Sallan
- Department of Earth and Environmental Sciences, University of Pennsylvania, Philadelphia, PA, United States of America
- Department of Biology, University of Pennsylvania, Philadelphia, PA, United States of America
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Jones KE, Dickson BV, Angielczyk KD, Pierce SE. Adaptive landscapes challenge the "lateral-to-sagittal" paradigm for mammalian vertebral evolution. Curr Biol 2021; 31:1883-1892.e7. [PMID: 33657406 DOI: 10.1016/j.cub.2021.02.009] [Citation(s) in RCA: 29] [Impact Index Per Article: 9.7] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/20/2020] [Revised: 01/08/2021] [Accepted: 02/03/2021] [Indexed: 11/28/2022]
Abstract
The evolution of mammals from their extinct forerunners, the non-mammalian synapsids, is one of the most iconic locomotor transitions in the vertebrate fossil record. In the limb skeleton, the synapsid-mammal transition is traditionally characterized by a shift from a sprawling limb posture, resembling that of extant reptiles and amphibians, to more adducted limbs, as seen in modern-day mammals. Based on proposed postural similarities between early synapsids and extant reptiles, this change is thought to be accompanied by a shift from ancestral reptile-like lateral bending to mammal-like sagittal bending of the vertebral column. To test this "lateral-to-sagittal" evolutionary paradigm, we used combinatorial optimization to produce functionally informed adaptive landscapes and determined the functional trade-offs associated with evolutionary changes in vertebral morphology. We show that the synapsid adaptive landscape is different from both extant reptiles and mammals, casting doubt on the reptilian model for early synapsid axial function, or indeed for the ancestral condition of amniotes more broadly. Further, the synapsid-mammal transition is characterized by not only increasing sagittal bending in the posterior column but also high stiffness and increasing axial twisting in the anterior column. Therefore, we refute the simplistic lateral-to-sagittal hypothesis and instead suggest the synapsid-mammal locomotor transition involved a more complex suite of functional changes linked to increasing regionalization of the backbone. These results highlight the importance of fossil taxa for understanding major evolutionary transitions.
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Affiliation(s)
- Katrina E Jones
- Museum of Comparative Zoology and Department of Organismic and Evolutionary Biology, Harvard University, 26 Oxford Street, Cambridge, MA 02138, USA; Department of Earth and Environmental Sciences, University of Manchester, Williamson Building, Oxford Road, Manchester M13 9PL, UK.
| | - Blake V Dickson
- Museum of Comparative Zoology and Department of Organismic and Evolutionary Biology, Harvard University, 26 Oxford Street, Cambridge, MA 02138, USA; Department of Evolutionary Anthropology, Duke University, Biological Sciences Building, 130 Science Drive, Durham, NC 27708, USA
| | - Kenneth D Angielczyk
- Negaunee Integrative Research Center, Field Museum of Natural History, 1400 South Lake Shore Drive, Chicago, IL 60605-2496, USA
| | - Stephanie E Pierce
- Museum of Comparative Zoology and Department of Organismic and Evolutionary Biology, Harvard University, 26 Oxford Street, Cambridge, MA 02138, USA.
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11
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Zink C, Schlehr MR. Working Dog Structure: Evaluation and Relationship to Function. Front Vet Sci 2020; 7:559055. [PMID: 33195533 PMCID: PMC7606876 DOI: 10.3389/fvets.2020.559055] [Citation(s) in RCA: 6] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/05/2020] [Accepted: 09/03/2020] [Indexed: 11/13/2022] Open
Abstract
Working dogs help to keep society and individuals safe, secure, and healthy. To perform their varied functions, it is critical to select dogs that are structurally sound and capable of demonstrating power, coordination and agility. Characteristics such as size and substance, head and axial skeletal structure, chest size and conformation, and thoracic and pelvic limb angulation should be evaluated to select the optimal combination of characteristics to suit the tasks to which each dog will be assigned. This review provides guidance on how to evaluate each of these structural components and discusses the contributions of those body parts to a working dog's function.
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Affiliation(s)
- Chris Zink
- Zink Integrative Sports Medicine, Ellicott City, MD, United States
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12
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Capano JG. Reaction Forces and Rib Function During Locomotion in Snakes. Integr Comp Biol 2020; 60:215-231. [PMID: 32396605 DOI: 10.1093/icb/icaa033] [Citation(s) in RCA: 6] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/14/2022] Open
Abstract
Locomotion in most tetrapods involves coordinated efforts between appendicular and axial musculoskeletal systems, where interactions between the limbs and the ground generate vertical (GV), horizontal (GH), and mediolateral (GML) ground-reaction forces that are transmitted to the axial system. Snakes have a complete absence of external limbs and represent a fundamental shift from this perspective. The axial musculoskeletal system of snakes is their primary structure to exert, transmit, and resist all motive and reaction forces for propulsion. Their lack of limbs makes them particularly dependent on the mechanical interactions between their bodies and the environment to generate the net GH they need for forward locomotion. As organisms that locomote on their bellies, the forces that enable the various modes of snake locomotion involve two important structures: the integument and the ribs. Snakes use the integument to contact the substrate and produce a friction-reservoir that exceeds their muscle-induced propulsive forces through modulation of scale stiffness and orientation, enabling propulsion through variable environments. XROMM work and previous studies suggest that the serially repeated ribs of snakes change their cross-sectional body shape, deform to environmental irregularities, provide synergistic stabilization for other muscles, and differentially exert and transmit forces to control propulsion. The costovertebral joints of snakes have a biarticular morphology, relative to the unicapitate costovertebral joints of other squamates, that appears derived and not homologous with the ancestral bicapitate ribs of Amniota. Evidence suggests that the biarticular joints of snakes may function to buttress locomotor forces, similar to other amniotes, and provide a passive mechanism for resisting reaction forces during snake locomotion. Future comparisons with other limbless lizard taxa are necessary to tease apart the mechanics and mechanisms that produced the locomotor versatility observed within Serpentes.
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Affiliation(s)
- John G Capano
- Department of Ecology and Evolutionary Biology, Brown University, Providence, RI 02912, USA
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Jones KE, Angielczyk KD, Pierce SE. Stepwise shifts underlie evolutionary trends in morphological complexity of the mammalian vertebral column. Nat Commun 2019; 10:5071. [PMID: 31699978 PMCID: PMC6838112 DOI: 10.1038/s41467-019-13026-3] [Citation(s) in RCA: 18] [Impact Index Per Article: 3.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/12/2019] [Accepted: 10/11/2019] [Indexed: 11/09/2022] Open
Abstract
A fundamental concept in evolutionary biology is that life tends to become more complex through geologic time, but empirical examples of this phenomenon are controversial. One debate is whether increasing complexity is the result of random variations, or if there are evolutionary processes which actively drive its acquisition, and if these processes act uniformly across clades. The mammalian vertebral column provides an opportunity to test these hypotheses because it is composed of serially-repeating vertebrae for which complexity can be readily measured. Here we test seven competing hypotheses for the evolution of vertebral complexity by incorporating fossil data from the mammal stem lineage into evolutionary models. Based on these data, we reject Brownian motion (a random walk) and uniform increasing trends in favor of stepwise shifts for explaining increasing complexity. We hypothesize that increased aerobic capacity in non-mammalian cynodonts may have provided impetus for increasing vertebral complexity in mammals.
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Affiliation(s)
- Katrina E Jones
- Museum of Comparative Zoology and Department of Organismic and Evolutionary Biology, Harvard University, 26 Oxford Street, Cambridge, MA, 02138, USA.
| | - Kenneth D Angielczyk
- Integrative Research Center, Field Museum of Natural History, 1400 South Lake Shore Drive, Chicago, IL, 60605-2496, USA
| | - Stephanie E Pierce
- Museum of Comparative Zoology and Department of Organismic and Evolutionary Biology, Harvard University, 26 Oxford Street, Cambridge, MA, 02138, USA.
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Galbusera F, Bassani T. The Spine: A Strong, Stable, and Flexible Structure with Biomimetics Potential. Biomimetics (Basel) 2019; 4:E60. [PMID: 31480241 PMCID: PMC6784295 DOI: 10.3390/biomimetics4030060] [Citation(s) in RCA: 16] [Impact Index Per Article: 3.2] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/26/2019] [Revised: 08/26/2019] [Accepted: 08/27/2019] [Indexed: 02/07/2023] Open
Abstract
From its first appearance in early vertebrates, the spine evolved the function of protecting the spinal cord, avoiding excessive straining during body motion. Its stiffness and strength provided the basis for the development of the axial skeleton as the mechanical support of later animals, especially those which moved to the terrestrial environment where gravity loads are not alleviated by the buoyant force of water. In tetrapods, the functions of the spine can be summarized as follows: protecting the spinal cord; supporting the weight of the body, transmitting it to the ground through the limbs; allowing the motion of the trunk, through to its flexibility; providing robust origins and insertions to the muscles of trunk and limbs. This narrative review provides a brief perspective on the development of the spine in vertebrates, first from an evolutionary, and then from an embryological point of view. The paper describes functions and the shape of the spine throughout the whole evolution of vertebrates and vertebrate embryos, from primordial jawless fish to extant animals such as birds and humans, highlighting its fundamental features such as strength, stability, and flexibility, which gives it huge potential as a basis for bio-inspired technologies.
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Affiliation(s)
- Fabio Galbusera
- Laboratory of Biological Structures Mechanics, IRCCS Istituto Ortopedico Galeazzi, 20161 Milan, Italy.
| | - Tito Bassani
- Laboratory of Biological Structures Mechanics, IRCCS Istituto Ortopedico Galeazzi, 20161 Milan, Italy
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15
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Jones KE, Angielczyk KD, Polly PD, Head JJ, Fernandez V, Lungmus JK, Tulga S, Pierce SE. Fossils reveal the complex evolutionary history of the mammalian regionalized spine. Science 2018; 361:1249-1252. [DOI: 10.1126/science.aar3126] [Citation(s) in RCA: 40] [Impact Index Per Article: 6.7] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/30/2017] [Revised: 04/27/2018] [Accepted: 07/25/2018] [Indexed: 11/02/2022]
Affiliation(s)
- K. E. Jones
- Museum of Comparative Zoology and Department of Organismic and Evolutionary Biology, Harvard University, Cambridge, MA 02138, USA
| | - K. D. Angielczyk
- Integrative Research Center, Field Museum of Natural History, Chicago, IL 60605, USA
| | - P. D. Polly
- Department of Earth and Atmospheric Sciences, Indiana University, Bloomington, IN 47405, USA
| | - J. J. Head
- Department of Zoology and University Museum of Zoology, University of Cambridge, Cambridge CB2 3EJ, UK
| | - V. Fernandez
- European Synchrotron Radiation Facility, 38000 Grenoble, France
| | - J. K. Lungmus
- Department of Organismal Biology and Anatomy, University of Chicago, Chicago, IL 60637, USA
| | - S. Tulga
- Department of Geophysical Sciences, University of Chicago, Chicago, IL 60637, USA
| | - S. E. Pierce
- Museum of Comparative Zoology and Department of Organismic and Evolutionary Biology, Harvard University, Cambridge, MA 02138, USA
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16
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Abstract
Because the musculoskeletal anatomy of the trunk is the framework for the behaviors of locomotion, ventilation, and body support in lepidosaurs, comparative study of trunk anatomy in this group is critical for unraveling the selective pressures leading to extant diversity in axial form and function among vertebrates. This work uses gross dissection and computed tomography to describe the muscular and skeletal anatomy of the trunk of varanid lizards (Varanidae, Anguimorpha). Gross muscle dissections were conducted to investigate the axial muscular anatomy of Varanus exanthematicus, Varanus giganteus, Varanus rosenbergi, and Varanus panoptes. Computed tomography scans of these and additional varanid lizards from the Varanus and Odatria subgenera were conducted to investigate rib and vertebral number and gross morphology. The number of vertebrae differs between species, with 27-35 presacral and 47-137 postsacral vertebrae. Although the number of floating and abdominal ribs in varanids is variable, most species examined have three to four cervical ribs and three true ribs. Attachment and insertion points of the epaxial and hypaxial musculature are detailed. The body wall has four main hypaxial layers, from superficial to deep: oliquus externus, intercostalis externi, intercostalis internii, and transversus. Varanids differ from other investigated lepidosaurs in having supracostalis dorsus brevis (epaxial) and levator costae (hypaxial), which independently connect each rib to the vertebral column. Although more basic muscle descriptions of the body wall in reptiles are needed, comparisons with the condition in the green iguana (Iguana iguana) can be made.
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Affiliation(s)
- Robert L Cieri
- Department of Biology, University of Utah, Salt Lake City, UT, USA
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17
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Penning DA. Quantitative axial myology in two constricting snakes: Lampropeltis holbrooki and Pantherophis obsoletus. J Anat 2018; 232:1016-1024. [PMID: 29484639 PMCID: PMC5979636 DOI: 10.1111/joa.12799] [Citation(s) in RCA: 11] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Accepted: 01/31/2018] [Indexed: 11/27/2022] Open
Abstract
A snake's body represents an extreme degree of elongation with immense muscle complexity. Snakes have approximately 25 different muscles on each side of the body at each vertebra. These muscles serially repeat, overlap, interconnect, and rarely insert parallel to the vertebral column. The angled muscles mean that simple measurements of anatomical cross-sectional area (ACSA, perpendicular to the long-axis of the body) serve only as proxies for the primary determinant of muscle force, physiological cross-sectional area (PCSA, area perpendicular to the muscle fibers). Here, I describe and quantify the musculature of two intraguild constrictors: kingsnakes (Lampropeltis holbrooki) and ratsnakes (Pantherophis obsoletus) whose predation performance varies considerably. Kingsnakes can produce significantly higher constriction pressures compared with ratsnakes of similar size. In both snakes, I provide qualitative descriptions, detail previously undescribed complexity, identify a new lateral muscle, and provide some of the first quantitative measures of individual muscle and whole-body PCSA. Furthermore, I compare measurements of ACSA with measurements of PCSA. There was no significant difference in PCSA of muscles between kingsnakes and ratsnakes. There is, however, a strong relationship between ACSA and PCSA measurements. I could not identify a significant difference in musculature between kingsnakes and ratsnakes that explains their different levels of constriction performance. Unmeasured components of muscle function, such as endurance and force production, might account for differences in performance between two species with similar muscle structure.
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Affiliation(s)
- David A. Penning
- Department of Biology & Environmental HealthMissouri Southern State UniversityJoplinMOUSA
- Department of BiologyUniversity of Louisiana at LafayetteLafayetteLAUSA
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18
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Jean-Xavier C, Perreault MC. Influence of Brain Stem on Axial and Hindlimb Spinal Locomotor Rhythm Generating Circuits of the Neonatal Mouse. Front Neurosci 2018; 12:53. [PMID: 29479302 PMCID: PMC5811543 DOI: 10.3389/fnins.2018.00053] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/29/2017] [Accepted: 01/23/2018] [Indexed: 12/18/2022] Open
Abstract
The trunk plays a pivotal role in limbed locomotion. Yet, little is known about how the brain stem controls trunk activity during walking. In this study, we assessed the spatiotemporal activity patterns of axial and hindlimb motoneurons (MNs) during drug-induced fictive locomotor-like activity (LLA) in an isolated brain stem-spinal cord preparation of the neonatal mouse. We also evaluated the extent to which these activity patterns are affected by removal of brain stem. Recordings were made in the segments T7, L2, and L5 using calcium imaging from individual axial MNs in the medial motor column (MMC) and hindlimb MNs in lateral motor column (LMC). The MN activities were analyzed during both the rhythmic and the tonic components of LLA, the tonic component being used as a readout of generalized increase in excitability in spinal locomotor networks. The most salient effect of brain stem removal was an increase in locomotor rhythm frequency and a concomitant reduction in burst durations in both MMC and LMC MNs. The lack of effect on the tonic component of LLA indicated specificity of action during the rhythmic component. Cooling-induced silencing of the brain stem reproduced the increase in rhythm frequency and accompanying decrease in burst durations in L2 MMC and LMC, suggesting a dependency on brain stem neuron activity. The work supports the idea that the brain stem locomotor circuits are operational already at birth and further suggests an important role in modulating trunk activity. The brain stem may influence the axial and hindlimb spinal locomotor rhythm generating circuits by extending their range of operation. This may represent a critical step of locomotor development when learning how to walk in different conditions and environments is a major endeavor.
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Affiliation(s)
| | - Marie-Claude Perreault
- Department of Physiology, Emory University School of Medicine, Atlanta, GA, United States
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19
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Shape Covariation (or the Lack Thereof) Between Vertebrae and Other Skeletal Traits in Felids: The Whole is Not Always Greater than the Sum of Parts. Evol Biol 2018; 45:196-210. [PMID: 29755151 PMCID: PMC5938317 DOI: 10.1007/s11692-017-9443-6] [Citation(s) in RCA: 15] [Impact Index Per Article: 2.5] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/12/2017] [Accepted: 12/18/2017] [Indexed: 12/25/2022]
Abstract
Within carnivorans, cats show comparatively little disparity in overall morphology, with species differing mainly in body size. However, detailed shape analyses of individual osteological structures, such as limbs or skulls, have shown that felids display significant morphological differences that correlate with their observed ecological and behavioural ranges. Recently, these shape analyses have been extended to the felid axial skeleton. Results demonstrate a functionally-partitioned vertebral column, with regions varying greatly in level of correlation between shape and ecology. Moreover, a clear distinction is evident between a phylogenetically-constrained neck region and a selection-responsive posterior spine. Here, we test whether this regionalisation of function reflected in vertebral column shape is also translated into varying levels of phenotypic integration between this structure and most other skeletal elements. We accomplish this comparison by performing pairwise tests of integration between vertebral and other osteological units, quantified with 3D geometric morphometric data and analysed both with and without phylogenetic correction. To our knowledge, this is the first study to test for integration across a comprehensive sample of whole-skeleton elements. Our results show that, prior to corrections, strong covariation is present between vertebrae across the vertebral column and all other elements, with the exception of the femur. However, most of these significant correlations disappear after correcting for phylogeny, which is a significant influence on cranial and limb morphology of felids and other carnivorans. Our results thus suggest that the vertebral column of cats displays relative independence from other skeletal elements and may represent several distinct evolutionary morphological modules.
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20
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Rossi GS, Turko AJ, Wright PA. Oxygen drives skeletal muscle remodeling in an amphibious fish out of water. J Exp Biol 2018; 221:jeb.180257. [PMID: 29691310 DOI: 10.1242/jeb.180257] [Citation(s) in RCA: 9] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/05/2018] [Accepted: 04/17/2018] [Indexed: 01/24/2023]
Abstract
Skeletal muscle remodeling in response to terrestrial acclimation improves the locomotor performance of some amphibious fishes on land, but the cue for this remodeling is unknown. We tested the hypothesis that muscle remodeling in the amphibious Kryptolebias marmoratus on land is driven by higher O2 availability in atmospheric air, and the alternative hypothesis that remodeling is induced by a different environmental or physiological condition fish experience on land. Fish were acclimated to 28 days of air, aquatic hyperoxia, hypercapnia, hypoxia, elevated temperature, or fasting conditions. Air, fasting, and hyperoxic conditions increased (>25%) the size of oxidative fibers in K. marmoratus while hypoxia had the reverse effect (23% decrease). Surprisingly, hyperoxia-acclimation also resulted in a transformation of the musculature to include large bands of oxidative-like muscle. Our results show that K. marmoratus is highly responsive to environmental O2 levels and capitalize on O2-rich opportunities to enhance O2 utilization by skeletal muscle.
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Affiliation(s)
- Giulia S. Rossi
- Department of Integrative Biology, University of Guelph, N1G 2W1, Canada
| | - Andy J. Turko
- Department of Integrative Biology, University of Guelph, N1G 2W1, Canada
| | - Patricia A. Wright
- Department of Integrative Biology, University of Guelph, N1G 2W1, Canada
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21
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Lewandowski D, Dubińska-Magiera M, Posyniak E, Rupik W, Daczewska M. Does the grass snake (Natrix natrix) (Squamata: Serpentes: Natricinae) fit the amniotes-specific model of myogenesis? PROTOPLASMA 2017; 254:1507-1516. [PMID: 27834030 PMCID: PMC5487930 DOI: 10.1007/s00709-016-1040-5] [Citation(s) in RCA: 6] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Figures] [Subscribe] [Scholar Register] [Received: 06/23/2016] [Accepted: 10/27/2016] [Indexed: 06/06/2023]
Abstract
In the grass snake (Natrix natrix), the newly developed somites form vesicles that are located on both sides of the neural tube. The walls of the vesicles are composed of tightly connected epithelial cells surrounding the cavity (the somitocoel). Also, in the newly formed somites, the Pax3 protein can be observed in the somite wall cells. Subsequently, the somite splits into three compartments: the sclerotome, dermomyotome (with the dorsomedial [DM] and the ventrolateral [VL] lips) and the myotome. At this stage, the Pax3 protein is detected in both the DM and VL lips of the dermomyotome and in the mononucleated cells of the myotome, whereas the Pax7 protein is observed in the medial part of the dermomyotome and in some of the mononucleated cells of the myotome. The mononucleated cells then become elongated and form myotubes. As myogenesis proceeds, the myotome is filled with multinucleated myotubes accompanied by mononucleated, Pax7-positive cells (satellite cells) that are involved in muscle growth. The Pax3-positive progenitor muscle cells are no longer observed. Moreover, we have observed unique features in the differentiation of the muscles in these snakes. Specifically, our studies have revealed the presence of two classes of muscles in the myotomes. The first class is characterised by fast muscle fibres, with myofibrils equally distributed throughout the sarcoplasm. In the second class, composed of slow muscle fibres, the sarcoplasm is filled with lipid droplets. We assume that their storage could play a crucial role during hibernation in the adult snakes. We suggest that the model of myotomal myogenesis in reptiles, birds and mammals shows the same morphological and molecular character. We therefore believe that the grass snake, in spite of the unique features of its myogenesis, fits into the amniotes-specific model of trunk muscle development.
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Affiliation(s)
- Damian Lewandowski
- Department of Animal Developmental Biology, Institute of Experimental Biology, University of Wroclaw, Sienkiewicza 21, 50-335, Wroclaw, Poland
| | - Magda Dubińska-Magiera
- Department of Animal Developmental Biology, Institute of Experimental Biology, University of Wroclaw, Sienkiewicza 21, 50-335, Wroclaw, Poland
| | - Ewelina Posyniak
- Department of Animal Developmental Biology, Institute of Experimental Biology, University of Wroclaw, Sienkiewicza 21, 50-335, Wroclaw, Poland
| | - Weronika Rupik
- Department of Animal Histology and Embryology, University of Silesia, Bankowa 9, 40-007, Katowice, Poland
| | - Małgorzata Daczewska
- Department of Animal Developmental Biology, Institute of Experimental Biology, University of Wroclaw, Sienkiewicza 21, 50-335, Wroclaw, Poland.
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22
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Jones KE. New insights on equid locomotor evolution from the lumbar region of fossil horses. Proc Biol Sci 2017; 283:rspb.2015.2947. [PMID: 27122554 DOI: 10.1098/rspb.2015.2947] [Citation(s) in RCA: 10] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/10/2015] [Accepted: 03/31/2016] [Indexed: 11/12/2022] Open
Abstract
The specialization of equid limbs for cursoriality is a classic case of adaptive evolution, but the role of the axial skeleton in this famous transition is not well understood. Extant horses are extremely fast and efficient runners, which use a stiff-backed gallop with reduced bending of the lumbar region relative to other mammals. This study tests the hypothesis that stiff-backed running in horses evolved in response to evolutionary increases in body size by examining lumbar joint shape from a broad sample of fossil equids in a phylogenetic context. Lumbar joint shape scaling suggests that stability of the lumbar region does correlate with size through equid evolution. However, scaling effects were dampened in the posterior lumbar region, near the sacrum, which suggests strong selection for sagittal mobility in association with locomotor-respiratory coupling near the lumbosacral joint. I hypothesize that small-bodied fossil horses may have used a speed-dependent running gait, switching between stiff-backed and flex-backed galloping as speed increased.
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Affiliation(s)
- Katrina Elizabeth Jones
- Center for Functional Anatomy and Evolution, Johns Hopkins University, 1830 East Monument St., Baltimore, MD 21205, USA
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23
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Halsey LG, Coward SRL, Crompton RH, Thorpe SKS. Practice makes perfect: Performance optimisation in 'arboreal' parkour athletes illuminates the evolutionary ecology of great ape anatomy. J Hum Evol 2017; 103:45-52. [PMID: 28166907 DOI: 10.1016/j.jhevol.2016.11.005] [Citation(s) in RCA: 9] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/06/2016] [Revised: 11/18/2016] [Accepted: 11/24/2016] [Indexed: 10/20/2022]
Abstract
An animal's size is central to its ecology, yet remarkably little is known about the selective pressures that drive this trait. A particularly compelling example is how ancestral apes evolved large body mass in such a physically and energetically challenging environment as the forest canopy, where weight-bearing branches and lianas are flexible, irregular and discontinuous, and the majority of preferred foods are situated on the most flexible branches at the periphery of tree crowns. To date the issue has been intractable due to a lack of relevant fossil material, the limited capacity of the fossil record to reconstruct an animal's behavioural ecology and the inability to measure energy consumption in freely moving apes. We studied the oxygen consumption of parkour athletes while they traversed an arboreal-like course as an elite model ape, to test the ecomorphological and behavioural mechanisms by which a large-bodied ape could optimize its energetic performance during tree-based locomotion. Our results show that familiarity with the arboreal-like course allowed the athletes to substantially reduce their energy expenditure. Furthermore, athletes with larger arm spans and shorter legs were particularly adept at finding energetic savings. Our results flesh out the scanty fossil record to offer evidence that long, strong arms, broad chests and a strong axial system, combined with the frequent use of uniform branch-to-branch arboreal pathways, were critical to off-setting the mechanical and energetic demands of large mass in ancestral apes.
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Affiliation(s)
- Lewis G Halsey
- Centre for Research in Ecology, Department of Life Sciences, University of Roehampton, Holybourne Avenue, London, SW15 4JD, UK.
| | - Samuel R L Coward
- School of Biosciences, University of Birmingham, Edgbaston, Birmingham, B15 2TT, UK.
| | - Robin H Crompton
- Department of Musculoskeletal Biology, Institute of Aging and Chronic Disease, University of Liverpool, Ashton Street, Liverpool, L69 3GE, UK.
| | - Susannah K S Thorpe
- School of Biosciences, University of Birmingham, Edgbaston, Birmingham, B15 2TT, UK.
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24
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Young BA, Dumais J, John N, Lyons B, Macduff A, Most M, Reiser NA, Reiser PJ. Functional Segregation within the Muscles of Aquatic Propulsion in the Asiatic Water Monitor (Varanus salvator). Front Physiol 2016; 7:380. [PMID: 27660612 PMCID: PMC5014869 DOI: 10.3389/fphys.2016.00380] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/14/2016] [Accepted: 08/22/2016] [Indexed: 11/26/2022] Open
Abstract
Water monitor lizards (Varanus salvator) swim using sinusoidal oscillations generated at the base of their long (50% of total body length) tail. In an effort to determine which level of the structural/organizational hierarchy of muscle is associated with functional segregation between the muscles of the tail base, an array of muscle features-myosin heavy chain profiles, enzymatic fiber types, twitch and tetanic force production, rates of fatigue, muscle compliance, and electrical activity patterns-were quantitated. The two examined axial muscles, longissimus, and iliocaudalis, were generally similar at the molecular, biochemical, and physiological levels, but differed at the biomechanics level and in their activation pattern. The appendicular muscle examined, caudofemoralis, differed from the axial muscles particularly at the molecular and physiological levels, and it exhibited a unique compliance profile and pattern of electrical activation. There were some apparent contradictions between the different structural/organizational levels examined. These contradictions, coupled with a unique myosin heavy chain profile, lead to the hypothesis that there are previously un-described molecular/biochemical specializations within varanid skeletal muscles.
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Affiliation(s)
- Bruce A. Young
- Department of Anatomy, Kirksville College of Osteopathic Medicine, A.T. Still University of Health SciencesKirksville, MO, USA
| | - Jessica Dumais
- Department of Physical Therapy, University of Massachusetts LowellLowell, MA, USA
| | - Nicholas John
- Department of Physical Therapy, University of Massachusetts LowellLowell, MA, USA
| | - Brandon Lyons
- Department of Physical Therapy, University of Massachusetts LowellLowell, MA, USA
| | - Andrew Macduff
- Department of Physical Therapy, University of Massachusetts LowellLowell, MA, USA
| | - Matthew Most
- Department of Physical Therapy, University of Massachusetts LowellLowell, MA, USA
| | - Nathan A. Reiser
- Department of Biosciences, College of Dentistry, Ohio State UniversityColumbus, OH, USA
| | - Peter J. Reiser
- Department of Biosciences, College of Dentistry, Ohio State UniversityColumbus, OH, USA
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25
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Oliver JD, Jones KE, Hautier L, Loughry WJ, Pierce SE. Vertebral bending mechanics and xenarthrous morphology in the nine-banded armadillo (Dasypus novemcinctus). ACTA ACUST UNITED AC 2016; 219:2991-3002. [PMID: 27473436 DOI: 10.1242/jeb.142331] [Citation(s) in RCA: 19] [Impact Index Per Article: 2.4] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/03/2016] [Accepted: 07/14/2016] [Indexed: 01/07/2023]
Abstract
The vertebral column has evolved to accommodate the broad range of locomotor pressures found across vertebrate lineages. Xenarthran (armadillos, sloths and anteaters) vertebral columns are characterized by xenarthrous articulations, novel intervertebral articulations located in the posterior trunk that are hypothesized to stiffen the vertebral column to facilitate digging. To determine the degree to which xenarthrous articulations impact vertebral movement, we passively measured compliance and range of motion during ventroflexion, dorsiflexion and lateral bending across the thoracolumbar region of the nine-banded armadillo, Dasypus novemcinctus Patterns of bending were compared with changes in vertebral morphology along the column to determine which morphological features best predict intervertebral joint mechanics. We found that compliance was lower in post-diaphragmatic, xenarthrous vertebrae relative to pre-xenarthrous vertebrae in both sagittal and lateral planes of bending. However, we also found that range of motion was higher in this region. These changes in mechanics are correlated with the transition from pre-xenarthrous to xenarthrous vertebrae, as well as with the transition from thoracic to lumbar vertebrae. Our results thus substantiate the hypothesis that xenarthrous articulations stiffen the vertebral column. Additionally, our data suggest that xenarthrous articulations, and their associated enlarged metapophyses, also act to increase the range of motion of the post-diaphragmatic region. We propose that xenarthrous articulations perform the dual role of stiffening the vertebral column and increasing mobility, resulting in passively stable vertebrae that are capable of substantial bending under appropriate loads.
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Affiliation(s)
- Jillian D Oliver
- Museum of Comparative Zoology and Department of Organismic and Evolutionary Biology, Harvard University, Cambridge, MA 02138, USA
| | - Katrina E Jones
- Museum of Comparative Zoology and Department of Organismic and Evolutionary Biology, Harvard University, Cambridge, MA 02138, USA
| | - Lionel Hautier
- Institut des Sciences de l'Evolution, UMR 5554, CNRS, IRD, EPHE, Université de Montpellier, 34090 Montpellier, France
| | - W J Loughry
- Department of Biology, Valdosta State University, Valdosta, GA 31698-0015, 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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26
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Diogo R, Bello‐Hellegouarch G, Kohlsdorf T, Esteve‐Altava B, Molnar JL. Comparative Myology and Evolution of Marsupials and Other Vertebrates, With Notes on Complexity, Bauplan, and “Scala Naturae”. Anat Rec (Hoboken) 2016; 299:1224-55. [DOI: 10.1002/ar.23390] [Citation(s) in RCA: 23] [Impact Index Per Article: 2.9] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/16/2016] [Revised: 05/06/2016] [Accepted: 05/09/2016] [Indexed: 11/05/2022]
Affiliation(s)
- Rui Diogo
- Department of AnatomyHoward University College of MedicineWashington DC USA
| | | | - Tiana Kohlsdorf
- Department of BiologyFFCLRP, University of São Paulo, Avenida BandeirantesRibeirão Preto SP Brazil
| | - Borja Esteve‐Altava
- Department of AnatomyHoward University College of MedicineWashington DC USA
- Structure and Motion Laboratory Department of Comparative Biomedical SciencesRoyal Veterinary College, Hawkshead Lane, HatfieldHertfordshireAL9 7TA UK
| | - Julia L. Molnar
- Department of AnatomyHoward University College of MedicineWashington DC USA
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27
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Randau M, Goswami A, Hutchinson JR, Cuff AR, Pierce SE. Cryptic complexity in felid vertebral evolution: shape differentiation and allometry of the axial skeleton. Zool J Linn Soc 2016. [DOI: 10.1111/zoj.12403] [Citation(s) in RCA: 38] [Impact Index Per Article: 4.8] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/27/2022]
Affiliation(s)
- Marcela Randau
- Department of Genetics, Evolution and Environment; University College London; London UK
| | - Anjali Goswami
- Department of Genetics, Evolution and Environment; University College London; London UK
| | - John R. Hutchinson
- Department of Genetics, Evolution and Environment; University College London; London UK
- Department of Comparative Biomedical Sciences and Structure & Motion Laboratory; The Royal Veterinary College; Hertfordshire UK
| | - Andrew R. Cuff
- Department of Genetics, Evolution and Environment; University College London; London UK
- Department of Comparative Biomedical Sciences and Structure & Motion Laboratory; The Royal Veterinary College; Hertfordshire UK
| | - Stephanie E. Pierce
- Department of Comparative Biomedical Sciences and Structure & Motion Laboratory; The Royal Veterinary College; Hertfordshire UK
- Museum of Comparative Zoology and Department of Organismic and Evolutionary Biology; Harvard University; Cambridge MA USA
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28
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Molnar JL, Pierce SE, Bhullar BAS, Turner AH, Hutchinson JR. Morphological and functional changes in the vertebral column with increasing aquatic adaptation in crocodylomorphs. ROYAL SOCIETY OPEN SCIENCE 2015; 2:150439. [PMID: 26716001 PMCID: PMC4680616 DOI: 10.1098/rsos.150439] [Citation(s) in RCA: 32] [Impact Index Per Article: 3.6] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Received: 08/28/2015] [Accepted: 10/07/2015] [Indexed: 05/26/2023]
Abstract
The lineage leading to modern Crocodylia has undergone dramatic evolutionary changes in morphology, ecology and locomotion over the past 200+ Myr. These functional innovations may be explained in part by morphological changes in the axial skeleton, which is an integral part of the vertebrate locomotor system. Our objective was to estimate changes in osteological range of motion (RoM) and intervertebral joint stiffness of thoracic and lumbar vertebrae with increasing aquatic adaptation in crocodylomorphs. Using three-dimensional virtual models and morphometrics, we compared the modern crocodile Crocodylus to five extinct crocodylomorphs: Terrestrisuchus, Protosuchus, Pelagosaurus, Steneosaurus and Metriorhynchus, which span the spectrum from terrestrial to fully aquatic. In Crocodylus, we also experimentally measured changes in trunk flexibility with sequential removal of osteoderms and soft tissues. Our results for the more aquatic species matched our predictions fairly well, but those for the more terrestrial early crocodylomorphs did not. A likely explanation for this lack of correspondence is the influence of other axial structures, particularly the rigid series of dorsal osteoderms in early crocodylomorphs. The most important structures for determining RoM and stiffness of the trunk in Crocodylus were different in dorsoventral versus mediolateral bending, suggesting that changes in osteoderm and rib morphology over crocodylomorph evolution would have affected movements in some directions more than others.
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Affiliation(s)
- Julia L. Molnar
- Department of Anatomy, Howard University College of Medicine, Washington, DC 20059, USA
- Structure and Motion Lab, Department of Comparative Biomedical Sciences, The Royal Veterinary College, Hawkshead Lane, Hatfield, Hertfordshire AL9 7TA, UK
| | - Stephanie E. Pierce
- Museum of Comparative Zoology and Department of Organismic and Evolutionary Biology, Harvard University, Cambridge, MA 02138, USA
- Structure and Motion Lab, Department of Comparative Biomedical Sciences, The Royal Veterinary College, Hawkshead Lane, Hatfield, Hertfordshire AL9 7TA, UK
| | | | - Alan H. Turner
- Department of Anatomical Sciences, Stonybrook University, Stony Brook, NY 11794, USA
| | - John R. Hutchinson
- Structure and Motion Lab, Department of Comparative Biomedical Sciences, The Royal Veterinary College, Hawkshead Lane, Hatfield, Hertfordshire AL9 7TA, UK
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Fuchs A, Anders A, Nolte I, Schilling N. Limb and back muscle activity adaptations to tripedal locomotion in dogs. ACTA ACUST UNITED AC 2015. [DOI: 10.1002/jez.1936] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022]
Affiliation(s)
- Aniela Fuchs
- Small Animal Clinic; University of Veterinary Medicine Hannover; Foundation; Hannover Germany
| | - Alexandra Anders
- Institute of Systematic Zoology and Evolutionary Biology; Friedrich-Schiller-University; Jena Germany
| | - Ingo Nolte
- Small Animal Clinic; University of Veterinary Medicine Hannover; Foundation; Hannover Germany
| | - Nadja Schilling
- Institute of Systematic Zoology and Evolutionary Biology; Friedrich-Schiller-University; Jena Germany
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Libourel PA, Herrel A. Sleep in amphibians and reptiles: a review and a preliminary analysis of evolutionary patterns. Biol Rev Camb Philos Soc 2015; 91:833-66. [DOI: 10.1111/brv.12197] [Citation(s) in RCA: 39] [Impact Index Per Article: 4.3] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/25/2014] [Revised: 04/22/2015] [Accepted: 04/28/2015] [Indexed: 01/18/2023]
Affiliation(s)
- Paul-Antoine Libourel
- SLEEP - Physiopathologie des Réseaux Neuronaux du Cycle Sommeil, Centre de Recherche en Neurosciences de Lyon, Inserm U1028 - CNRS UMR5292, Faculté de Médecine Laennec; 7 rue Guillaume Paradin 69372 Lyon Cedex 08 France
| | - Anthony Herrel
- Département d'Ecologie et de Gestion de la Biodiversité; UMR 7179 C.N.R.S/M.N.H.N.; 57 rue Cuvier, Case Postale 55 75231 Paris Cedex 05 France
- Evolutionary Morphology of Vertebrates; Ghent University; K.L. Ledeganckstraat 35 B-9000 Gent Belgium
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Omura A, Ejima K, Honda K, Anzai W, Taguchi Y, Koyabu D, Endo H. Locomotion pattern and trunk musculoskeletal architecture among Urodela. ACTA ZOOL-STOCKHOLM 2015; 96:225-235. [PMID: 25914411 PMCID: PMC4402012 DOI: 10.1111/azo.12070] [Citation(s) in RCA: 8] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Accepted: 01/09/2014] [Indexed: 11/28/2022]
Abstract
We comparatively examined the trunk musculature and prezygapophyseal angle of mid-trunk vertebra in eight urodele species with different locomotive modes (aquatic Siren intermedia, Amphiuma tridactylum, Necturus maculosus and Andrias japonicus; semi-aquatic Cynops pyrrhogaster, Cynops ensicauda; and terrestrial Hynobius nigrescens, Hynobius lichenatus and Ambystoma tigrinum). We found that the more terrestrial species were characterized by larger dorsal and abdominal muscle weight ratios compared with those of the more aquatic species, whereas muscle ratios of the lateral hypaxial musculature were larger in the more aquatic species. The lateral hypaxial muscles were thicker in the more aquatic species, whereas the M. rectus abdominis was more differentiated in the more terrestrial species. Our results suggest that larger lateral hypaxial muscles function for lateral bending during underwater locomotion in aquatic species. Larger dorsalis and abdominal muscles facilitate resistance against sagittal extension of the trunk, stabilization and support of the ventral contour line against gravity in terrestrial species. The more aquatic species possessed a more horizontal prezygapophyseal angle for more flexible lateral locomotion. In contrast, the more terrestrial species have an increasingly vertical prezygapophyseal angle to provide stronger column support against gravity. Thus, we conclude trunk structure in urodeles differs clearly according to their locomotive modes.
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Affiliation(s)
- Ayano Omura
- Graduate School of Agricultural and Life Sciences The University Museum The University of Tokyo 7‐3‐1 Hongo, Bunkyo‐ku Tokyo 113‐0033 Japan
- The University Museum The University of Tokyo 7‐3‐1 Hongo, Bunkyo‐ku Tokyo 113‐0033 Japan
| | - Ken‐Ichiro Ejima
- Department of Oral and Maxillofacial Radiology Nihon University School of Dentistry 1‐8‐13, Kanda‐Surugadai, Chiyoda‐ku Tokyo 101‐8310 Japan
| | - Kazuya Honda
- Department of Oral and Maxillofacial Radiology Nihon University School of Dentistry 1‐8‐13, Kanda‐Surugadai, Chiyoda‐ku Tokyo 101‐8310 Japan
- Division of Systemic Biology and Oncology Dental Research Center Nihon University School of Dentistry 1‐8‐13, Kanda‐Surugadai, Chiyoda‐ku Tokyo 101‐8310 Japan
| | - Wataru Anzai
- The University Museum The University of Tokyo 7‐3‐1 Hongo, Bunkyo‐ku Tokyo 113‐0033 Japan
- Graduate School of Biological Sciences The University Museum The University of Tokyo 7‐3‐1 Hongo, Bunkyo‐ku Tokyo 113‐0033 Japan
| | - Yuki Taguchi
- Hiroshima City Asa Zoological Park Asa‐tyou Doubutsuen Asakita‐ku Hiroshima City Hiroshima 731‐3355 Japan
| | - Daisuke Koyabu
- The University Museum The University of Tokyo 7‐3‐1 Hongo, Bunkyo‐ku Tokyo 113‐0033 Japan
| | - Hideki Endo
- The University Museum The University of Tokyo 7‐3‐1 Hongo, Bunkyo‐ku Tokyo 113‐0033 Japan
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Omura A, Anzai W, Koyabu D, Endo H. Ontogenetic changes of trunk muscle structure in the Japanese black salamander (Hynobius nigrescens). J Vet Med Sci 2015; 77:931-6. [PMID: 25816856 PMCID: PMC4565815 DOI: 10.1292/jvms.15-0011] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022] Open
Abstract
We investigated ontogenetic changes in the trunk muscles of the Japanese black salamander (Hynobius nigrescens) before, during and after metamorphosis. Given that amphibians change their locomotive patterns with metamorphosis, we hypothesized that they may also change the structure of their trunk muscles. The trunk muscles were macroscopically observed, and the weight ratios of each trunk muscle group were quantified at six different developmental stages. Immediately after hatching, we found that the lateral hypaxial muscle was composed of one thick M. ventralis, from ventral edge of which M. transversus abdominis arose later, followed by M. obliquus externus and M. rectus abdominis. The weight ratios of the dorsal and abdominal muscles to the trunk muscles increased with growth. We suggest that a single thick and large lateral hypaxial muscle facilitates swimming during early developmental
stages. The increase in the weight ratios of the dorsal and abdominal muscles with growth possibly assists with gravity resistance necessary for terrestrial life.
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Affiliation(s)
- Ayano Omura
- Graduate School of Agricultural and Life Sciences, The University Museum, The University of Tokyo, 7-3-1 Hongo, Bunkyo-ku, Tokyo 113-0033, Japan
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Jones KE. Evolutionary allometry of the thoracolumbar centra in felids and bovids. J Morphol 2015; 276:818-31. [PMID: 25773228 DOI: 10.1002/jmor.20382] [Citation(s) in RCA: 21] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/21/2014] [Revised: 01/29/2015] [Accepted: 02/03/2015] [Indexed: 11/07/2022]
Abstract
Mammals have evolved a remarkable range of body sizes, yet their overall body plan remains unaltered. One challenge of evolutionary biology is to understand the mechanisms by which this size diversity is achieved, and how the mechanical challenges associated with changing body size are overcome. Despite the importance of the axial skeleton in body support and locomotion, and much interest in the allometry of the appendicular skeleton, little is known about vertebral allometry outside primates. This study compares evolutionary allometry of the thoracolumbar centra in two families of quadrupedal running mammals: Felidae and Bovidae. I test the hypothesis that, as size increases, the thoracolumbar region will resist increasing loads by becoming a) craniocaudally shorter, and b) larger in cross-sectional area, particularly in the sagittal plane. Length, width, and height of the thoracolumbar centra of 23 felid and 34 bovid species were taken. Thoracic, prediaphragmatic, lumbar, and postdiaphragmatic lengths were calculated, and diameters were compared at three equivalent positions: the midthoracic, the diaphragmatic and the midlumbar vertebra. Allometric slopes were calculated using a reduced major axis regression, on both raw and independent contrasts data. Slopes and elevations were compared using an ANCOVA. As size increases the thoracolumbar centra become more robust, showing preferential reinforcement in the sagittal plane. There was less allometric shortening of the thoracic than the lumbar region, perhaps reflecting constraints due to its connection with the respiratory apparatus. The thoracic region was more robust in bovids than felids, whereas the lumbar region was longer and more robust in felids than bovids. Elongation of lumbar centra increases the outlever of sagittal bending at intervertebral joints, increasing the total pelvic displacement during dorsomobile running. Both locomotor specializations and functional regionalization of the axial skeleton appear to have influenced its response to increasing size.
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Affiliation(s)
- Katrina E Jones
- Center for Functional Anatomy and Evolution, Johns Hopkins University, 1830 East Monument st., Baltimore, Maryland, USA
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35
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Aberrant back muscle function correlates with intramuscular architecture of dorsovertebral muscles in two-toed sloths. Mamm Biol 2015. [DOI: 10.1016/j.mambio.2015.01.002] [Citation(s) in RCA: 13] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/19/2022]
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Ryczko D, Knüsel J, Crespi A, Lamarque S, Mathou A, Ijspeert AJ, Cabelguen JM. Flexibility of the axial central pattern generator network for locomotion in the salamander. J Neurophysiol 2014; 113:1921-40. [PMID: 25540227 DOI: 10.1152/jn.00894.2014] [Citation(s) in RCA: 20] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/09/2023] Open
Abstract
In tetrapods, limb and axial movements are coordinated during locomotion. It is well established that inter- and intralimb coordination show considerable variations during ongoing locomotion. Much less is known about the flexibility of the axial musculoskeletal system during locomotion and the neural mechanisms involved. Here we examined this issue in the salamander Pleurodeles waltlii, which is capable of locomotion in both aquatic and terrestrial environments. Kinematics of the trunk and electromyograms from the mid-trunk epaxial myotomes were recorded during four locomotor behaviors in freely moving animals. A similar approach was used during rhythmic struggling movements since this would give some insight into the flexibility of the axial motor system. Our results show that each of the forms of locomotion and the struggling behavior is characterized by a distinct combination of mid-trunk motor patterns and cycle durations. Using in vitro electrophysiological recordings in isolated spinal cords, we observed that the spinal networks activated with bath-applied N-methyl-d-aspartate could generate these axial motor patterns. In these isolated spinal cord preparations, the limb motor nerve activities were coordinated with each mid-trunk motor pattern. Furthermore, isolated mid-trunk spinal cords and hemicords could generate the mid-trunk motor patterns. This indicates that each side of the cord comprises a network able to generate coordinated axial motor activity. The roles of descending and sensory inputs in the behavior-related changes in axial motor coordination are discussed.
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Affiliation(s)
- D Ryczko
- Institut National de la Santé et de la Recherche Médicale (INSERM) U 862-Neurocentre Magendie, Université de Bordeaux, Bordeaux Cedex, France; and
| | - J Knüsel
- Biorobotics Laboratory (BIOROB), Institute of Bioengineering, Ecole Polytechnique Fédérale de Lausanne (EPFL), Lausanne, Switzerland
| | - A Crespi
- Biorobotics Laboratory (BIOROB), Institute of Bioengineering, Ecole Polytechnique Fédérale de Lausanne (EPFL), Lausanne, Switzerland
| | - S Lamarque
- Institut National de la Santé et de la Recherche Médicale (INSERM) U 862-Neurocentre Magendie, Université de Bordeaux, Bordeaux Cedex, France; and
| | - A Mathou
- Institut National de la Santé et de la Recherche Médicale (INSERM) U 862-Neurocentre Magendie, Université de Bordeaux, Bordeaux Cedex, France; and
| | - A J Ijspeert
- Biorobotics Laboratory (BIOROB), Institute of Bioengineering, Ecole Polytechnique Fédérale de Lausanne (EPFL), Lausanne, Switzerland
| | - J M Cabelguen
- Institut National de la Santé et de la Recherche Médicale (INSERM) U 862-Neurocentre Magendie, Université de Bordeaux, Bordeaux Cedex, France; and
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Burrows AM, Durham EL, Matthews LC, Smith TD, Parr LA. Of mice, monkeys, and men: physiological and morphological evidence for evolutionary divergence of function in mimetic musculature. Anat Rec (Hoboken) 2014; 297:1250-61. [PMID: 24706483 PMCID: PMC4051843 DOI: 10.1002/ar.22913] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/23/2013] [Accepted: 02/15/2014] [Indexed: 11/09/2022]
Abstract
Facial expression is a universal means of visual communication in humans and many other primates. Humans have the most complex facial display repertoire among primates; however, gross morphological studies have not found greater complexity in human mimetic musculature. This study examines the microanatomical aspects of mimetic musculature to test the hypotheses related to human mimetic musculature physiology, function, and evolutionary morphology. Samples from the orbicularis oris muscle (OOM) and the zygomaticus major (ZM) muscle in laboratory mice (N = 3), rhesus macaques (N = 3), and humans (N = 3) were collected. Fiber type proportions (slow-twitch and fast-twitch), fiber cross-sectional area, diameter, and length were calculated, and means were statistically compared among groups. Results showed that macaques had the greatest percentage of fast fibers in both muscles (followed by humans) and that humans had the greatest percentage of slow fibers in both muscles. Macaques and humans typically did not differ from one another in morphometrics except for fiber length where humans had longer fibers. Although sample sizes are low, results from this study may indicate that the rhesus macaque OOM and ZM muscle are specialized primarily to assist with maintenance of the rigid dominance hierarchy via rapid facial displays of submission and aggression, whereas human musculature may have evolved not only under pressure to work in facial expressions but also in development of speech.
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Affiliation(s)
- Anne M. Burrows
- Dept. of Physical Therapy, Duquesne University, Pittsburgh, PA
- Dept. of Anthropology, University of Pittsburgh, Pittsburgh, PA
| | - Emily L. Durham
- Dept. of Physical Therapy, Duquesne University, Pittsburgh, PA
| | - Lea C. Matthews
- Dept. of Health Management Systems, Duquesne University, Pittsburgh, PA
| | - Timothy D. Smith
- Dept. of Anthropology, University of Pittsburgh, Pittsburgh, PA
- School of Physical Therapy, Slippery Rock University, Slippery Rock, PA
| | - Lisa A. Parr
- Dept. of Psychiatry and Behavioral Science, Center for Translational Neuroscience, Yerkes National Primate Research Center, Emory University, Atlanta, GA
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Abstract
Trunk musculature in Urodela species varies by habitat. In this study, trunk musculature was examined in five species of adult salamanders representing three different habitats: aquatic species, Amphiuma tridactylum and Necturus maculosus; semi-aquatic species, Cynops pyrrhogaster; terrestrial species, Hynobius nigrescens and Ambystoma tigrinum. More terrestrial species have heavier dorsal and ventral trunk muscles than more aquatic forms. By contrast, the lateral hypaxial musculature was stronger in more aquatic species. The number of layers of lateral hypaxial musculature varied among Urodela species and did not clearly correlate with their habitats. The M. rectus abdominis was separated from the lateral hypaxial musculature in both terrestrial and semi-aquatic species. In aquatic species, M. rectus abdominis was not separated from lateral hypaxial musculature. Lateral hypaxial musculature differed in thickness among species and was relatively thinner in terrestrial species. In more terrestrial species, dorsal muscles may be used for stabilization and ventral flexing against gravity. Ventral muscle may be used in preventing dorsally concave curvature of the trunk by dorsal muscles and by weight. The lengthy trunk supported by limbs needs muscular forces along the ventral contour line in more terrestrial species. And, the locomotion on well-developed limbs seems to lead to a decrease of the lateral hypaxial musculature.
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Affiliation(s)
- Ayano Omura
- Graduate School of Agricultural and Life Sciences, The University Museum, The University of Tokyo, 7-3-1 Hongo, Bunkyo-ku, Tokyo 113-0033, Japan
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Abstract
Locomotion requires precise control of spinal networks. In tetrapods and bipeds, dynamic regulation of locomotion is simplified by the modular organization of spinal limb circuits, but it is not known whether their predecessors, fish axial circuits, are similarly organized. Here, we demonstrate that the larval zebrafish spinal cord contains distinct, parallel microcircuits for independent control of dorsal and ventral musculature on each side of the body. During normal swimming, dorsal and ventral microcircuits are equally active, but, during postural correction, fish differentially engage these microcircuits to generate torque for self-righting. These findings reveal greater complexity in the axial spinal networks responsible for swimming than previously recognized and suggest an early template of modular organization for more-complex locomotor circuits in later vertebrates.
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Affiliation(s)
- Martha W. Bagnall
- Department of Neurobiology, Northwestern University, Evanston IL 60208, USA
| | - David L. McLean
- Department of Neurobiology, Northwestern University, Evanston IL 60208, USA
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Dawson R, Milne N, Warburton NM. Muscular anatomy of the tail of the western grey kangaroo, Macropus fuliginosus. AUST J ZOOL 2014. [DOI: 10.1071/zo13085] [Citation(s) in RCA: 9] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/23/2022]
Abstract
The western grey kangaroo, Macropus fuliginosus, is a large-bodied kangaroo that engages in pentapedal locomotion at low speeds and bipedal hopping at high speeds. The tail is thought to have functional roles in both of these modes of locomotion. In pentapedal locomotion the tail acts as a ‘fifth limb’ to support the body weight together with the forelimbs while the hind limbs are drawn forward. The tail has also been suggested to have a role as a counterbalance during bipedal hopping. On the basis of these functional roles for the tail in locomotion, the caudal musculature of the western grey kangaroo was dissected and described in this study. The arrangement of the caudal musculature showed particular adaptations for the role of the tail in both pentapedal locomotion and bipedal hopping.
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Functional differentiation of the human lumbar perivertebral musculature revisited by means of muscle fibre type composition. Ann Anat 2013; 195:570-80. [DOI: 10.1016/j.aanat.2013.07.003] [Citation(s) in RCA: 14] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/21/2013] [Revised: 07/21/2013] [Accepted: 07/23/2013] [Indexed: 11/19/2022]
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Cabelguen JM, Charrier V, Mathou A. Modular functional organisation of the axial locomotor system in salamanders. ZOOLOGY 2013; 117:57-63. [PMID: 24290785 DOI: 10.1016/j.zool.2013.10.002] [Citation(s) in RCA: 6] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/12/2013] [Revised: 10/10/2013] [Accepted: 10/14/2013] [Indexed: 11/26/2022]
Abstract
Most investigations on tetrapod locomotion have been concerned with limb movements. However, there is compelling evidence that the axial musculoskeletal system contributes to important functions during locomotion. Adult salamanders offer a remarkable opportunity to examine these functions because these amphibians use axial undulations to propel themselves in both aquatic and terrestrial environments. In this article, we review the currently available biological data on axial functions during various locomotor modes in salamanders. We also present data showing the modular organisation of the neural networks that generate axial synergies during locomotion. The functional implication of this modular organisation is discussed.
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Affiliation(s)
- Jean-Marie Cabelguen
- Neurocentre Magendie, INSERM U 862, Bordeaux University, 146 rue Léo Saignat, F-33077 Bordeaux Cedex, France.
| | - Vanessa Charrier
- Neurocentre Magendie, INSERM U 862, Bordeaux University, 146 rue Léo Saignat, F-33077 Bordeaux Cedex, France
| | - Alexia Mathou
- Neurocentre Magendie, INSERM U 862, Bordeaux University, 146 rue Léo Saignat, F-33077 Bordeaux Cedex, France
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43
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Neufuss J, Hesse B, Thorpe SKS, Vereecke EE, D'Aout K, Fischer MS, Schilling N. Fibre type composition in the lumbar perivertebral muscles of primates: implications for the evolution of orthogrady in hominoids. J Anat 2013; 224:113-31. [PMID: 24433382 DOI: 10.1111/joa.12130] [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] [Accepted: 09/25/2013] [Indexed: 11/28/2022] Open
Abstract
The axial musculoskeletal system is important for the static and dynamic control of the body during both locomotor and non-locomotor behaviour. As a consequence, major evolutionary changes in the positional habits of a species are reflected by morpho-functional adaptations of the axial system. Because of the remarkable phenotypic plasticity of muscle tissue, a close relationship exists between muscle morphology and function. One way to explore major evolutionary transitions in muscle function is therefore by comparative analysis of fibre type composition. In this study, the three-dimensional distribution of slow and fast muscle fibres was analysed in the lumbar perivertebral muscles of two lemuriform (mouse lemur, brown lemur) and four hominoid primate species (white-handed gibbon, orangutan, bonobo, chimpanzee) in order to develop a plausible scenario for the evolution of the contractile properties of the axial muscles in hominoids and to discern possible changes in muscle physiology that were associated with the evolution of orthogrady. Similar to all previously studied quadrupedal mammals, the lemuriform primates in this study exhibited a morpho-functional dichotomy between deep slow contracting local stabilizer muscles and superficial fast contracting global mobilizers and stabilizers and thus retained the fibre distribution pattern typical for quadrupedal non-primates. In contrast, the hominoid primates showed no regionalization of the fibre types, similar to previous observations in Homo. We suggest that this homogeneous fibre composition is associated with the high functional versatility of the axial musculature that was brought about by the evolution of orthograde behaviours and reflects the broad range of mechanical demands acting on the trunk in orthograde hominoids. Because orthogrady is a derived character of euhominoids, the uniform fibre type distribution is hypothesized to coincide with the evolution of orthograde behaviours.
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Affiliation(s)
- J Neufuss
- Institute of Systematic Zoology and Evolutionary Biology, Friedrich-Schiller-University, Jena, Germany; Department of Human Evolution, Max Planck Institute for Evolutionary Anthropology, Leipzig, Germany
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Charrier V, Cabelguen JM. Fictive rhythmic motor patterns produced by the tail spinal cord in salamanders. Neuroscience 2013; 255:191-202. [PMID: 24161283 DOI: 10.1016/j.neuroscience.2013.10.020] [Citation(s) in RCA: 8] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/16/2013] [Revised: 09/11/2013] [Accepted: 10/10/2013] [Indexed: 11/18/2022]
Abstract
Most investigations into the role of the body axis in vertebrate locomotion have focused on the trunk, although in most tetrapods, the tail also plays an active role. In salamanders, the tail contributes to propulsion during swimming and to dynamic balance and maneuverability during terrestrial locomotion. The aim of the present study was to obtain information concerning the neural mechanisms that produce tail muscle contractions during locomotion in the salamander Pleurodeles waltlii. We recorded the ventral root activities in in vitro spinal cord preparations in which locomotor-like activity was induced via bath application of N-methyl-d-aspartate (20μM) and d-serine (10μM). Recordings showed that the tail spinal cord is capable of producing propagated waves of motor activity that alternate between the left and right sides. Lesion experiments further revealed that the tail rhythmogenic network is composed of a double chain of identical hemisegmental oscillators. Finally, using spinal cord preparations bathed in a chamber partitioned into two pools, we revealed efficient short-distance coupling between the trunk and tail networks. Together, our results demonstrate the existence of a pattern generator for rhythmic tail movements in the salamander and show that the global architecture of the tail network is similar to that previously proposed for the mid-trunk locomotor network in the salamander. Our findings further support the view that salamanders can control their trunk and tail independently during stepping movements. The relevance of our results in relation to the generation of tail muscle contractions in freely moving salamanders is discussed.
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Affiliation(s)
- V Charrier
- Neurocentre Magendie, INSERM U 862 - Université de Bordeaux, 146 rue Léo Saignat, F-33077 Bordeaux Cedex, France.
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Trinajstic K, Sanchez S, Dupret V, Tafforeau P, Long J, Young G, Senden T, Boisvert C, Power N, Ahlberg PE. Fossil musculature of the most primitive jawed vertebrates. Science 2013; 341:160-4. [PMID: 23765280 DOI: 10.1126/science.1237275] [Citation(s) in RCA: 35] [Impact Index Per Article: 3.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/02/2022]
Abstract
The transition from jawless to jawed vertebrates (gnathostomes) resulted in the reconfiguration of the muscles and skeleton of the head, including the creation of a separate shoulder girdle with distinct neck muscles. We describe here the only known examples of preserved musculature from placoderms (extinct armored fishes), the phylogenetically most basal jawed vertebrates. Placoderms possess a regionalized muscular anatomy that differs radically from the musculature of extant sharks, which is often viewed as primitive for gnathostomes. The placoderm data suggest that neck musculature evolved together with a dermal joint between skull and shoulder girdle, not as part of a broadly flexible neck as in sharks, and that transverse abdominal muscles are an innovation of gnathostomes rather than of tetrapods.
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Affiliation(s)
- Kate Trinajstic
- Western Australian Organic and Isotope Geochemistry Centre, Department of Chemistry, Curtin University, Perth, Western Australia 6102, Australia
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Pittman M, Gatesy SM, Upchurch P, Goswami A, Hutchinson JR. Shake a tail feather: the evolution of the theropod tail into a stiff aerodynamic surface. PLoS One 2013; 8:e63115. [PMID: 23690987 PMCID: PMC3655181 DOI: 10.1371/journal.pone.0063115] [Citation(s) in RCA: 24] [Impact Index Per Article: 2.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/09/2012] [Accepted: 04/02/2013] [Indexed: 11/18/2022] Open
Abstract
Theropod dinosaurs show striking morphological and functional tail variation; e.g., a long, robust, basal theropod tail used for counterbalance, or a short, modern avian tail used as an aerodynamic surface. We used a quantitative morphological and functional analysis to reconstruct intervertebral joint stiffness in the tail along the theropod lineage to extant birds. This provides new details of the tail's morphological transformation, and for the first time quantitatively evaluates its biomechanical consequences. We observe that both dorsoventral and lateral joint stiffness decreased along the non-avian theropod lineage (between nodes Theropoda and Paraves). Our results show how the tail structure of non-avian theropods was mechanically appropriate for holding itself up against gravity and maintaining passive balance. However, as dorsoventral and lateral joint stiffness decreased, the tail may have become more effective for dynamically maintaining balance. This supports our hypothesis of a reduction of dorsoventral and lateral joint stiffness in shorter tails. Along the avian theropod lineage (Avialae to crown group birds), dorsoventral and lateral joint stiffness increased overall, which appears to contradict our null expectation. We infer that this departure in joint stiffness is specific to the tail's aerodynamic role and the functional constraints imposed by it. Increased dorsoventral and lateral joint stiffness may have facilitated a gradually improved capacity to lift, depress, and swing the tail. The associated morphological changes should have resulted in a tail capable of producing larger muscular forces to utilise larger lift forces in flight. Improved joint mobility in neornithine birds potentially permitted an increase in the range of lift force vector orientations, which might have improved flight proficiency and manoeuvrability. The tail morphology of modern birds with tail fanning capabilities originated in early ornithuromorph birds. Hence, these capabilities should have been present in the early Cretaceous, with incipient tail-fanning capacity in the earliest pygostylian birds.
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Affiliation(s)
- Michael Pittman
- Department of Earth Sciences, University College London, London, United Kingdom.
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Skedros JG, Knight AN, Clark GC, Crowder CM, Dominguez VM, Qiu S, Mulhern DM, Donahue SW, Busse B, Hulsey BI, Zedda M, Sorenson SM. Scaling of Haversian canal surface area to secondary osteon bone volume in ribs and limb bones. AMERICAN JOURNAL OF PHYSICAL ANTHROPOLOGY 2013; 151:230-44. [DOI: 10.1002/ajpa.22270] [Citation(s) in RCA: 36] [Impact Index Per Article: 3.3] [Reference Citation Analysis] [Track Full Text] [Subscribe] [Scholar Register] [Received: 05/30/2012] [Accepted: 03/06/2013] [Indexed: 11/11/2022]
Affiliation(s)
- John G. Skedros
- Department of Veterans Affairs Medical Center; Bone and Joint Research Laboratory; Salt Lake City; UT
| | - Alex N. Knight
- Department of Veterans Affairs Medical Center; Bone and Joint Research Laboratory; Salt Lake City; UT
| | - Gunnar C. Clark
- Department of Veterans Affairs Medical Center; Bone and Joint Research Laboratory; Salt Lake City; UT
| | - Christian M. Crowder
- Office of the Armed Forces Medical Examiner; Armed Forces Medical Examiner System; Dover AFB; DE
| | | | - Shijing Qiu
- Bone and Mineral Research Laboratory; Henry Ford Hospital; Detroit; MI
| | | | - Seth W. Donahue
- Department of Mechanical Engineering; Colorado State University; Fort Collins; CO
| | - Björn Busse
- Department of Osteology and Biomechanics (IOBM); University Medical Center Hamburg-Eppendorf; Hamburg; Germany
| | | | - Marco Zedda
- Department of Animal Biology; University of Sassari; Sassari; Italy
| | - Scott M. Sorenson
- Department of Veterans Affairs Medical Center; Bone and Joint Research Laboratory; Salt Lake City; UT
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Maes L, Abourachid A. Gait transitions and modular organization of mammal locomotion. ACTA ACUST UNITED AC 2013; 216:2257-65. [PMID: 23531814 DOI: 10.1242/jeb.082149] [Citation(s) in RCA: 20] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022]
Abstract
Quadrupedal locomotion is the result of complex interactions between biomechanical and neural systems. During steady gaits, both systems are in stable states. When the animal changes its speed, transitions between gaits can occur in which the different coordination parameters are dissociated. Consequently, transitions are the periods where it is possible to detect and identify those parameters involved in the mechanical or neural control of locomotion. We studied interlimb coordination using a sequential method (antero-posterior sequence) to measure the footfall patterns of dogs when accelerating and decelerating from 1.5 m s(-1) to more than 6 m s(-1) and back. We obtained 383 transitions between all the symmetrical and asymmetrical gaits used by the dogs. Analysis of the interlimb coordination modifications and of each foot parameter showed that mechanics drive the stance phase whereas coordination is controlled during the swing phase. Furthermore, comparison of the transition patterns between all gaits reveals the modular organization of locomotion: a pectoral module coordinates the two forelimbs, a pelvic module coordinates the two hindlimbs and an axial module coordinates the two pairs of limbs and the trunk motion. The three modules cooperate to give rise to a template of stable interlimb coordination pattern, such as walk, trot or gallop.
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Affiliation(s)
- Ludovic Maes
- Muséum National d'Histoire Naturelle-CNRS, Département EGB, UMR7179, Pavillon d'Anatomie Comparée, 55 Rue Buffon, 75231 Paris Cedex 05, France
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Marschallinger J, Obermayer A, Steinbacher P, Stoiber W. The zebrafish myotome contains tonic muscle fibers: morphological characterization and time course of formation. J Morphol 2013; 274:320-30. [PMID: 23280572 DOI: 10.1002/jmor.20095] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/01/2012] [Revised: 08/20/2012] [Accepted: 09/24/2012] [Indexed: 11/07/2022]
Abstract
It is long known that the skeletal muscle of teleost fish contains muscle fibers which are in all probability of a tonic type according to morphological criteria. However, the evidence for the existence of teleost tonic fibers is still confined to a very small number of species, and knowledge concerning their ontogeny and possible functions is even more restricted. A remarkable deficit in this context is that it is not even exactly known whether the zebrafish, which is widely used to study vertebrate developmental biology, has such fibers, or how they arise. The present study demonstrates the existence of tonic fibers in the zebrafish myotome. They are identical with a fiber population previously termed "red muscle rim" fibers. A combined histochemical, immunocytochemical, and ultrastructural approach is used to characterize the morphology and development of these fibers. This study provides a basis for using the zebrafish model system in the future research on the developmental regulation and the functions of tonic fibers.
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Affiliation(s)
- Julia Marschallinger
- Department of Organismic Biology, Division of Zoology and Functional Anatomy, University of Salzburg, Hellbrunnerstr. 34, A-5020 Salzburg, Austria.
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Buchholtz EA, Bailin HG, Laves SA, Yang JT, Chan MY, Drozd LE. Fixed cervical count and the origin of the mammalian diaphragm. Evol Dev 2012; 14:399-411. [PMID: 22947313 DOI: 10.1111/j.1525-142x.2012.00560.x] [Citation(s) in RCA: 40] [Impact Index Per Article: 3.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/30/2022]
Abstract
Why is mammalian cervical count fixed across the historically long and ecologically broad mammalian radiation? Multiple lines of evidence, considered together, suggest a link between fixed cervical count and the muscularization of the diaphragm, a key innovation in mammalian history. We test this hypothesis by documenting the anteroposterior (AP) movement of the diaphragm, a lateral plate derivative, relative to that of the somitic thoracolumbar transition in unusually patterned mammals, by comparing the temporal occurrence of an osteological proxy for the diaphragm and fixed cervical counts in the fossil record, and by quantifying morphological differentiation within the mammalian cervical series. We then integrate these anatomical observations with details of diaphragm function and development to propose a sequence of innovations in mammalian evolution that could have led to fixed cervical count. We argue that the novel commitment of migratory muscle precursor cells (MMPs) of mid-cervical somites to a fate in the abaxial diaphragm defined these somites as a new and uniquely mammalian modular subunit. We further argue that the coordination of primaxial abaxial patterning constrained subsequent AP migration of the forelimb, thereby secondarily fixing cervical count.
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Affiliation(s)
- Emily A Buchholtz
- Department of Biological Sciences, Wellesley College, Wellesley, MA 02481, USA.
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