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Jamie A Maclaren - One of the best experts on this subject based on the ideXlab platform.
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comparative forelimb myology and muscular architecture of a juvenile malayan tapir tapirus indicus
Journal of Anatomy, 2020Co-Authors: Jamie A Maclaren, Brianna K MchorseAbstract:: The absence of preserved soft tissues in the fossil record is frequently a hindrance for palaeontologists wishing to investigate morphological shifts in key skeletal systems, such as the limbs. Understanding the soft tissue composition of modern species can aid in understanding changes in musculoskeletal features through evolution, including those pertaining to locomotion. Establishing anatomical differences in soft tissues utilising an extant phylogenetic bracket can, in turn, assist in interpreting morphological changes in hard tissues and modelling musculoskeletal movements during evolutionary transitions (e.g. digit reduction in perissodactyls). Perissodactyls (horses, rhinoceroses, tapirs and their relatives) are known to have originated with a four-toed (tetradactyl) forelimb condition. Equids proceeded to reduce all but their central digit, resulting in monodactyly, whereas tapirs retained the ancestral tetradactyl state. The modern Malayan tapir (Tapirus indicus) has been shown to exhibit fully functional tetradactyly in its forelimb, more so than any other tapir, and represents an ideal case-study for muscular arrangement and architectural comparison with the highly derived monodactyl Equus. Here, we present the first quantification of muscular architecture of a tetradactyl perissodactyl (T. indicus), and compare it to measurements from modern monodactyl caballine horse (Equus ferus caballus). Each muscle of the tapir forelimb was dissected out from a cadaver and measured for architectural properties: muscle-tendon unit (MTU) length, MTU mass, muscle mass, pennation angle, and resting fibre length. Comparative parameters [physiological cross-sectional area (PCSA), muscle volume, and % muscle mass] were then calculated from the raw measurements. In the shoulder region, the infraspinatus of T. indicus exhibits dual origination sites on either side of the deflected scapular spine. Within ungulates, this condition has only been previously reported in suids. Differences in relative contribution to limb muscle mass between T. indicus and Equus highlight forelimb muscles that affect mobility in the lateral and medial digits (e.g. extensor digitorum lateralis). These muscles were likely reduced in equids during their evolutionary transition from tetradactyl forest-dwellers to monodactyl, open-habitat specialists. Patterns of PCSA across the forelimb were similar between T. indicus and Equus, with the notable exceptions of the biceps brachii and flexor carpi ulnaris, which were much larger in Equus. The differences observed in PCSA between the tapir and horse forelimb muscles highlight muscles that are essential for maintaining stability in the monodactyl limb while moving at high speeds. This quantitative dataset of muscle architecture in a functionally tetradactyl perissodactyl is a pivotal first step towards reconstructing the locomotor capabilities of extinct, four-toed ancestors of modern perissodactyls, and providing further insights into the equid locomotor transition.
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comparative forelimb myology and muscular architecture of a juvenile malayan tapir tapirus indicus
Journal of Anatomy, 2020Co-Authors: Jamie A Maclaren, Brianna K MchorseAbstract:The absence of preserved soft tissues in the fossil record is frequently a hindrance for palaeontologists wishing to investigate morphological shifts in key skeletal systems, such as the limbs. Understanding the soft tissue composition of modern species can aid in understanding changes in musculoskeletal features through evolution, including those pertaining to locomotion. Establishing anatomical differences in soft tissues utilising an extant phylogenetic bracket can, in turn, assist in interpreting morphological changes in hard tissues and modelling musculoskeletal movements during evolutionary transitions (e.g. digit reduction in perissodactyls). Perissodactyls (horses, rhinoceroses, tapirs and their relatives) are known to have originated with a four-toed (tetradactyl) forelimb condition. Equids proceeded to reduce all but their central digit, resulting in monodactyly, whereas tapirs retained the ancestral tetradactyl state. The modern Malayan tapir (Tapirus indicus) has been shown to exhibit fully functional tetradactyly in its forelimb, more so than any other tapir, and represents an ideal case-study for muscular arrangement and architectural comparison with the highly derived monodactyl Equus. Here, we present the first quantification of muscular architecture of a tetradactyl perissodactyl (T. indicus), and compare it to measurements from modern monodactyl caballine horse (Equus ferus caballus). Each muscle of the tapir forelimb was dissected out from a cadaver and measured for architectural properties: muscle-tendon unit (MTU) length, MTU mass, muscle mass, pennation angle, and resting fibre length. Comparative parameters [physiological cross-sectional area (PCSA), muscle volume, and % muscle mass] were then calculated from the raw measurements. In the shoulder region, the infraspinatus of T. indicus exhibits dual origination sites on either side of the deflected scapular spine. Within ungulates, this condition has only been previously reported in suids. Differences in relative contribution to limb muscle mass between T. indicus and Equus highlight forelimb muscles that affect mobility in the lateral and medial digits (e.g. extensor digitorum lateralis). These muscles were likely reduced in equids during their evolutionary transition from tetradactyl forest-dwellers to monodactyl, open-habitat specialists. Patterns of PCSA across the forelimb were similar between T. indicus and Equus, with the notable exceptions of the biceps brachii and flexor carpi ulnaris, which were much larger in Equus. The differences observed in PCSA between the tapir and horse forelimb muscles highlight muscles that are essential for maintaining stability in the monodactyl limb while moving at high speeds. This quantitative dataset of muscle architecture in a functionally tetradactyl perissodactyl is a pivotal first step towards reconstructing the locomotor capabilities of extinct, four-toed ancestors of modern perissodactyls, and providing further insights into the equid locomotor transition.
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Modern Tapirs as Morphofunctional Analogues for Locomotion in Endemic Eocene European Perissodactyls
Journal of Mammalian Evolution, 2019Co-Authors: Jamie A Maclaren, Sandra NauwelaertsAbstract:Tapirs have historically been considered as ecologically analogous to several groups of extinct perissodactyls based on dental and locomotor morphology. Here, we investigate comparative functional morphology between living tapirs and endemic Eocene European perissodactyls to ascertain whether tapirs represent viable analogues for locomotion in palaeotheres and lophiodontids. Forelimb bones from 20 species of Eocene European perissodactyls were laser scanned and compared to a forelimb dataset of extant Tapirus . Bone shape was quantified using 3D geometric morphometrics; coordinates were Procrustes aligned and compared using Principal Component Analysis and neighbor-joining trees. Functional traits included lever-arm ratios (LARs; proxy for joint angular velocity), long-bone proportions (speed proxy), and estimated body mass. Results suggest that Paralophiodon and Palaeotherium magnum resemble Neotropical tapirs in humeral morphology and LARs. Palaeotheres demonstrate extensive forelimb shape disparity. Despite previous assessments, metacarpal shape analyzes do not support a strong morphological similarity between palaeotheres and tapirs, with Tapirus pinchaque representing the closest analogue for Eocene European equoid manus morphology. Our analyses suggest lophiodontids were not capable of moving as swiftly as tapirs due to greater loading over the manus. We conclude that the variation within modern tapir forelimb morphology confounds the assignment of one living analogue within Tapirus for extinct European equoids, whereas tapirs adapted for greater loading over the manus (e.g., T. bairdii, T. indicus ) represent viable locomotor analogues for lophiodontids. This study represents a valuable first step toward locomotor simulation and behavioral inference for both hippomorph and tapiromorph perissodactyls in Eocene faunal communities.
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Interspecific variation in the tetradactyl manus of modern tapirs (Perissodactyla: Tapirus) exposed using geometric morphometrics.
Journal of morphology, 2017Co-Authors: Jamie A Maclaren, Sandra NauwelaertsAbstract:The distal forelimb (autopodium) of quadrupedal mammals is a key morphological unit involved in locomotion, body support, and interaction with the substrate. The manus of the tapir (Perissodactyla: Tapirus) is unique within modern perissodactyls, as it retains the plesiomorphic tetradactyl (four-toed) condition also exhibited by basal equids and rhinoceroses. Tapirs are known to exhibit anatomical mesaxonic symmetry in the manus, although interspecific differences and biomechanical mesaxony have yet to be rigorously tested. Here, we investigate variation in the manus morphology of four modern tapir species (Tapirus indicus, Tapirus bairdii, Tapirus pinchaque, and Tapirus terrestris) using a geometric morphometric approach. Autopodial bones were laser scanned to capture surface shape and morphology was quantified using 3D-landmark analysis. Landmarks were aligned using Generalised Procrustes Analysis, with discriminant function and partial least square analyses performed on aligned coordinate data to identify features that significantly separate tapir species. Overall, our results support the previously held hypothesis that T. indicus is morphologically separate from neotropical tapirs; however, previous conclusions regarding function from morphological differences are shown to require reassessment. We find evidence indicating that T. bairdii exhibits reduced reliance on the lateral fifth digit compared to other tapirs. Morphometric assessment of the metacarpophalangeal joint and the morphology of the distal facets of the lunate lend evidence toward high loading on the lateral digits of both the large T. indicus (large body mass) and the small, long limbed T. pinchaque (ground impact). Our results support other recent studies on T. pinchaque, suggesting subtle but important adaptations to a compliant but inclined habitat. In conclusion, we demonstrate further evidence that the modern tapir forelimb is a variable locomotor unit with a range of interspecific features tailored to habitual and biomechanical needs of each species.
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a three dimensional morphometric analysis of upper forelimb morphology in the enigmatic tapir Perissodactyla tapirus hints at subtle variations in locomotor ecology
Journal of Morphology, 2016Co-Authors: Jamie A Maclaren, Sandra NauwelaertsAbstract:Forelimb morphology is an indicator for terrestrial locomotor ecology. The limb morphology of the enigmatic tapir (Perissodactyla: Tapirus) has often been compared to that of basal perissodactyls, despite the lack of quantitative studies comparing forelimb variation in modern tapirs. Here, we present a quantitative assessment of tapir upper forelimb osteology using three-dimensional geometric morphometrics to test whether the four modern tapir species are monomorphic in their forelimb skeleton. The shape of the upper forelimb bones across four species (T. indicus; T. bairdii; T. terrestris; T. pinchaque) was investigated. Bones were laser scanned to capture surface morphology and 3D landmark analysis was used to quantify shape. Discriminant function analyses were performed to reveal features which could be used for interspecific discrimination. Overall our results show that the appendicular skeleton contains notable interspecific differences. We demonstrate that upper forelimb bones can be used to discriminate between species (>91% accuracy), with the scapula proving the most diagnostic bone (100% accuracy). Features that most successfully discriminate between the four species include the placement of the cranial angle of the scapula, depth of the humeral condyle, and the caudal deflection of the olecranon. Previous studies comparing the limbs of T. indicus and T. terrestris are corroborated by our quantitative findings. Moreover, the mountain tapir T. pinchaque consistently exhibited the greatest divergence in morphology from the other three species. Despite previous studies describing tapirs as functionally mediportal in their locomotor style, we find osteological evidence suggesting a spectrum of locomotor adaptations in the tapirs. We conclude that modern tapir forelimbs are neither monomorphic nor are tapirs as conserved in their locomotor habits as previously described. J. Morphol. 277:1469–1485, 2016. © 2016 Wiley Periodicals, Inc.
Sandra Nauwelaerts - One of the best experts on this subject based on the ideXlab platform.
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Modern Tapirs as Morphofunctional Analogues for Locomotion in Endemic Eocene European Perissodactyls
Journal of Mammalian Evolution, 2019Co-Authors: Jamie A Maclaren, Sandra NauwelaertsAbstract:Tapirs have historically been considered as ecologically analogous to several groups of extinct perissodactyls based on dental and locomotor morphology. Here, we investigate comparative functional morphology between living tapirs and endemic Eocene European perissodactyls to ascertain whether tapirs represent viable analogues for locomotion in palaeotheres and lophiodontids. Forelimb bones from 20 species of Eocene European perissodactyls were laser scanned and compared to a forelimb dataset of extant Tapirus . Bone shape was quantified using 3D geometric morphometrics; coordinates were Procrustes aligned and compared using Principal Component Analysis and neighbor-joining trees. Functional traits included lever-arm ratios (LARs; proxy for joint angular velocity), long-bone proportions (speed proxy), and estimated body mass. Results suggest that Paralophiodon and Palaeotherium magnum resemble Neotropical tapirs in humeral morphology and LARs. Palaeotheres demonstrate extensive forelimb shape disparity. Despite previous assessments, metacarpal shape analyzes do not support a strong morphological similarity between palaeotheres and tapirs, with Tapirus pinchaque representing the closest analogue for Eocene European equoid manus morphology. Our analyses suggest lophiodontids were not capable of moving as swiftly as tapirs due to greater loading over the manus. We conclude that the variation within modern tapir forelimb morphology confounds the assignment of one living analogue within Tapirus for extinct European equoids, whereas tapirs adapted for greater loading over the manus (e.g., T. bairdii, T. indicus ) represent viable locomotor analogues for lophiodontids. This study represents a valuable first step toward locomotor simulation and behavioral inference for both hippomorph and tapiromorph perissodactyls in Eocene faunal communities.
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Interspecific variation in the tetradactyl manus of modern tapirs (Perissodactyla: Tapirus) exposed using geometric morphometrics.
Journal of morphology, 2017Co-Authors: Jamie A Maclaren, Sandra NauwelaertsAbstract:The distal forelimb (autopodium) of quadrupedal mammals is a key morphological unit involved in locomotion, body support, and interaction with the substrate. The manus of the tapir (Perissodactyla: Tapirus) is unique within modern perissodactyls, as it retains the plesiomorphic tetradactyl (four-toed) condition also exhibited by basal equids and rhinoceroses. Tapirs are known to exhibit anatomical mesaxonic symmetry in the manus, although interspecific differences and biomechanical mesaxony have yet to be rigorously tested. Here, we investigate variation in the manus morphology of four modern tapir species (Tapirus indicus, Tapirus bairdii, Tapirus pinchaque, and Tapirus terrestris) using a geometric morphometric approach. Autopodial bones were laser scanned to capture surface shape and morphology was quantified using 3D-landmark analysis. Landmarks were aligned using Generalised Procrustes Analysis, with discriminant function and partial least square analyses performed on aligned coordinate data to identify features that significantly separate tapir species. Overall, our results support the previously held hypothesis that T. indicus is morphologically separate from neotropical tapirs; however, previous conclusions regarding function from morphological differences are shown to require reassessment. We find evidence indicating that T. bairdii exhibits reduced reliance on the lateral fifth digit compared to other tapirs. Morphometric assessment of the metacarpophalangeal joint and the morphology of the distal facets of the lunate lend evidence toward high loading on the lateral digits of both the large T. indicus (large body mass) and the small, long limbed T. pinchaque (ground impact). Our results support other recent studies on T. pinchaque, suggesting subtle but important adaptations to a compliant but inclined habitat. In conclusion, we demonstrate further evidence that the modern tapir forelimb is a variable locomotor unit with a range of interspecific features tailored to habitual and biomechanical needs of each species.
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a three dimensional morphometric analysis of upper forelimb morphology in the enigmatic tapir Perissodactyla tapirus hints at subtle variations in locomotor ecology
Journal of Morphology, 2016Co-Authors: Jamie A Maclaren, Sandra NauwelaertsAbstract:Forelimb morphology is an indicator for terrestrial locomotor ecology. The limb morphology of the enigmatic tapir (Perissodactyla: Tapirus) has often been compared to that of basal perissodactyls, despite the lack of quantitative studies comparing forelimb variation in modern tapirs. Here, we present a quantitative assessment of tapir upper forelimb osteology using three-dimensional geometric morphometrics to test whether the four modern tapir species are monomorphic in their forelimb skeleton. The shape of the upper forelimb bones across four species (T. indicus; T. bairdii; T. terrestris; T. pinchaque) was investigated. Bones were laser scanned to capture surface morphology and 3D landmark analysis was used to quantify shape. Discriminant function analyses were performed to reveal features which could be used for interspecific discrimination. Overall our results show that the appendicular skeleton contains notable interspecific differences. We demonstrate that upper forelimb bones can be used to discriminate between species (>91% accuracy), with the scapula proving the most diagnostic bone (100% accuracy). Features that most successfully discriminate between the four species include the placement of the cranial angle of the scapula, depth of the humeral condyle, and the caudal deflection of the olecranon. Previous studies comparing the limbs of T. indicus and T. terrestris are corroborated by our quantitative findings. Moreover, the mountain tapir T. pinchaque consistently exhibited the greatest divergence in morphology from the other three species. Despite previous studies describing tapirs as functionally mediportal in their locomotor style, we find osteological evidence suggesting a spectrum of locomotor adaptations in the tapirs. We conclude that modern tapir forelimbs are neither monomorphic nor are tapirs as conserved in their locomotor habits as previously described. J. Morphol. 277:1469–1485, 2016. © 2016 Wiley Periodicals, Inc.
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A three‐dimensional morphometric analysis of upper forelimb morphology in the enigmatic tapir (Perissodactyla: Tapirus) hints at subtle variations in locomotor ecology
Journal of morphology, 2016Co-Authors: Jamie A Maclaren, Sandra NauwelaertsAbstract:Forelimb morphology is an indicator for terrestrial locomotor ecology. The limb morphology of the enigmatic tapir (Perissodactyla: Tapirus) has often been compared to that of basal perissodactyls, despite the lack of quantitative studies comparing forelimb variation in modern tapirs. Here, we present a quantitative assessment of tapir upper forelimb osteology using three-dimensional geometric morphometrics to test whether the four modern tapir species are monomorphic in their forelimb skeleton. The shape of the upper forelimb bones across four species (T. indicus; T. bairdii; T. terrestris; T. pinchaque) was investigated. Bones were laser scanned to capture surface morphology and 3D landmark analysis was used to quantify shape. Discriminant function analyses were performed to reveal features which could be used for interspecific discrimination. Overall our results show that the appendicular skeleton contains notable interspecific differences. We demonstrate that upper forelimb bones can be used to discriminate between species (>91% accuracy), with the scapula proving the most diagnostic bone (100% accuracy). Features that most successfully discriminate between the four species include the placement of the cranial angle of the scapula, depth of the humeral condyle, and the caudal deflection of the olecranon. Previous studies comparing the limbs of T. indicus and T. terrestris are corroborated by our quantitative findings. Moreover, the mountain tapir T. pinchaque consistently exhibited the greatest divergence in morphology from the other three species. Despite previous studies describing tapirs as functionally mediportal in their locomotor style, we find osteological evidence suggesting a spectrum of locomotor adaptations in the tapirs. We conclude that modern tapir forelimbs are neither monomorphic nor are tapirs as conserved in their locomotor habits as previously described. J. Morphol. 277:1469–1485, 2016. © 2016 Wiley Periodicals, Inc.
Luke T. Holbrook - One of the best experts on this subject based on the ideXlab platform.
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Early Eocene fossils suggest that the mammalian order Perissodactyla originated in India
Nature communications, 2014Co-Authors: Kenneth D. Rose, Luke T. Holbrook, Rajendra S. Rana, Kishor Kumar, Katrina E. Jones, Heather E. Ahrens, Pieter Missiaen, Ashok Sahni, Thierry SmithAbstract:The phylogenetic and biogeographic origin of Perissodactyla (horses, rhinoceroses and tapirs) is unclear. Here the authors report 54.5 Myr fossils from a sister taxa of Perissodactyla found in India, which suggests that the group may have originated in India before its collision with Asia.
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Diversity and evolution of Hunter-Schreger Band configuration in tooth enamel of perissodactyl mammals
Acta Palaeontologica Polonica, 2011Co-Authors: Wighart Von Koenigswald, Luke T. Holbrook, Kenneth D. RoseAbstract:Four different Hunter-Schreger Band (HSB) configurations were observed in the teeth of fossil and extant Perissodactyla. This variability exceeds that observed in Artiodactyla or Proboscidea. The four HSB configurations represent two different evolutionary pathways. Transverse HSB found in many mammalian taxa outside the Perissodactyla represents the most primitive HSB configuration. It occurs in several primitive perissodactyl families and is retained in Palaeotheriidae and extant Equidae. Curved HSB evolved from transverse HSB and occurs in Tapiridae, Helaletidae, and Lophiodontidae, as well as in Ancylopoda and Titanotheriomorpha. This likely indicates independent evolution of curved HSB in two or more lineages, but the number of instances of parallelism of this configuration is obscured by uncertainty in the relationships among these taxa and by a lack of data for some important basal taxa. A second evolutionary pathway leads from transverse HSB via compound HSB to vertical HSB. Compound HSB were dete...
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osteology of lophiodon cuvier 1822 mammalia Perissodactyla and its phylogenetic implications
Journal of Vertebrate Paleontology, 2009Co-Authors: Luke T. HolbrookAbstract:ABSTRACT Lophiodon is the best-known member of the Lophiodontidae, a family of Eocene Eurasian perissodactyls, in terms of its skull and postcranial skeleton. Previous studies have allied Lophiodontidae with either Tapiroidea or Chalicotherioidea. This study describes the cranial and postcranial osteology of Lophiodon with an emphasis on characters pertaining to the phylogenetic position of lophiodontids. Although cranial and postcranial remains of Lophiodon are known from European faunas, the skull and postcranial skeleton have not been well studied, and few non-dental characters have been used to investigate the relationships of this genus to other perissodactyls. Lophiodon displays a mosaic of cranial and postcranial features that could be interpreted as possible synapomorphies uniting it with either tapiroids or chalicotherioids. Data collected from these studies were incorporated into a phylogenetic analysis of a variety of perissodactyl taxa scored for characters of the skull, postcranial skeleton, ...
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Skulls of the Eocene perissodactyls (Mammalia) Homogalax and Isectolophus
Journal of Vertebrate Paleontology, 2004Co-Authors: Luke T. Holbrook, Spencer G. Lucas, Robert J. EmryAbstract:Abstract We describe skulls of the Wasatchian perissodactyl Homogalax and the Bridgerian–Uintan perissodactyl Isectolophus from North America for the first time. These skulls provide information on cranial evolution in tapiromorph perissodactyls as well as on primitive character states for Perissodactyla as a whole. They confirm the retention of a primitive rostrum in these taxa, as Radinsky had previously stated without reference to particular specimens. Characters from skull morphology suggest that Homogalax and Isectolophus should not be included in the same family.
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The Phylogeny and Classification of Tapiromorph Perissodactyls (Mammalia)
Cladistics, 1999Co-Authors: Luke T. HolbrookAbstract:Despite an excellent fossil record, the phylogeny of Perissodactyla is not well understood, in terms of both the relationships within Perissodactyla and the position of the Perissodactyla among the orders of mammals. This paper provides a phylogenetic analysis of one major perissodactyl lineage, the Tapiromorpha. This analysis combines a more comprehensive sampling of characters and taxa with rigorous tree-searching methods to create a new hypothesis of tapiromorph relationships. The phylogeny of tapiromorph perissodactyls is analyzed using 45 characters of the skull, postcranial skeleton, and dentition scored for 29 taxa, including three nontapiromorph outgroups. Phylogenetic taxonomic definitions are constructed for suprageneric taxa. According to the results of this analysis, the Chalicotherioidea cannot be unequivocally assigned to the Tapiromorpha, nor can Homogalax or Cardiolophus. Isectolophus, Tapiroidea, and Rhinocerotoidea are unequivocal members of the Tapiromorpha. Heptodon is included in a monophyletic Tapiroidea. Amynodontid rhinocerotoids come out as the sister group to rhinocerotids, and indricotheres do not fall within the Hyracodontidae. The results of this study provide further arguments that tapiromorphs (and putative tapiromorphs) may be important for understanding the ancestral morphology of Perissodactyla.
Brianna K Mchorse - One of the best experts on this subject based on the ideXlab platform.
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comparative forelimb myology and muscular architecture of a juvenile malayan tapir tapirus indicus
Journal of Anatomy, 2020Co-Authors: Jamie A Maclaren, Brianna K MchorseAbstract:: The absence of preserved soft tissues in the fossil record is frequently a hindrance for palaeontologists wishing to investigate morphological shifts in key skeletal systems, such as the limbs. Understanding the soft tissue composition of modern species can aid in understanding changes in musculoskeletal features through evolution, including those pertaining to locomotion. Establishing anatomical differences in soft tissues utilising an extant phylogenetic bracket can, in turn, assist in interpreting morphological changes in hard tissues and modelling musculoskeletal movements during evolutionary transitions (e.g. digit reduction in perissodactyls). Perissodactyls (horses, rhinoceroses, tapirs and their relatives) are known to have originated with a four-toed (tetradactyl) forelimb condition. Equids proceeded to reduce all but their central digit, resulting in monodactyly, whereas tapirs retained the ancestral tetradactyl state. The modern Malayan tapir (Tapirus indicus) has been shown to exhibit fully functional tetradactyly in its forelimb, more so than any other tapir, and represents an ideal case-study for muscular arrangement and architectural comparison with the highly derived monodactyl Equus. Here, we present the first quantification of muscular architecture of a tetradactyl perissodactyl (T. indicus), and compare it to measurements from modern monodactyl caballine horse (Equus ferus caballus). Each muscle of the tapir forelimb was dissected out from a cadaver and measured for architectural properties: muscle-tendon unit (MTU) length, MTU mass, muscle mass, pennation angle, and resting fibre length. Comparative parameters [physiological cross-sectional area (PCSA), muscle volume, and % muscle mass] were then calculated from the raw measurements. In the shoulder region, the infraspinatus of T. indicus exhibits dual origination sites on either side of the deflected scapular spine. Within ungulates, this condition has only been previously reported in suids. Differences in relative contribution to limb muscle mass between T. indicus and Equus highlight forelimb muscles that affect mobility in the lateral and medial digits (e.g. extensor digitorum lateralis). These muscles were likely reduced in equids during their evolutionary transition from tetradactyl forest-dwellers to monodactyl, open-habitat specialists. Patterns of PCSA across the forelimb were similar between T. indicus and Equus, with the notable exceptions of the biceps brachii and flexor carpi ulnaris, which were much larger in Equus. The differences observed in PCSA between the tapir and horse forelimb muscles highlight muscles that are essential for maintaining stability in the monodactyl limb while moving at high speeds. This quantitative dataset of muscle architecture in a functionally tetradactyl perissodactyl is a pivotal first step towards reconstructing the locomotor capabilities of extinct, four-toed ancestors of modern perissodactyls, and providing further insights into the equid locomotor transition.
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comparative forelimb myology and muscular architecture of a juvenile malayan tapir tapirus indicus
Journal of Anatomy, 2020Co-Authors: Jamie A Maclaren, Brianna K MchorseAbstract:The absence of preserved soft tissues in the fossil record is frequently a hindrance for palaeontologists wishing to investigate morphological shifts in key skeletal systems, such as the limbs. Understanding the soft tissue composition of modern species can aid in understanding changes in musculoskeletal features through evolution, including those pertaining to locomotion. Establishing anatomical differences in soft tissues utilising an extant phylogenetic bracket can, in turn, assist in interpreting morphological changes in hard tissues and modelling musculoskeletal movements during evolutionary transitions (e.g. digit reduction in perissodactyls). Perissodactyls (horses, rhinoceroses, tapirs and their relatives) are known to have originated with a four-toed (tetradactyl) forelimb condition. Equids proceeded to reduce all but their central digit, resulting in monodactyly, whereas tapirs retained the ancestral tetradactyl state. The modern Malayan tapir (Tapirus indicus) has been shown to exhibit fully functional tetradactyly in its forelimb, more so than any other tapir, and represents an ideal case-study for muscular arrangement and architectural comparison with the highly derived monodactyl Equus. Here, we present the first quantification of muscular architecture of a tetradactyl perissodactyl (T. indicus), and compare it to measurements from modern monodactyl caballine horse (Equus ferus caballus). Each muscle of the tapir forelimb was dissected out from a cadaver and measured for architectural properties: muscle-tendon unit (MTU) length, MTU mass, muscle mass, pennation angle, and resting fibre length. Comparative parameters [physiological cross-sectional area (PCSA), muscle volume, and % muscle mass] were then calculated from the raw measurements. In the shoulder region, the infraspinatus of T. indicus exhibits dual origination sites on either side of the deflected scapular spine. Within ungulates, this condition has only been previously reported in suids. Differences in relative contribution to limb muscle mass between T. indicus and Equus highlight forelimb muscles that affect mobility in the lateral and medial digits (e.g. extensor digitorum lateralis). These muscles were likely reduced in equids during their evolutionary transition from tetradactyl forest-dwellers to monodactyl, open-habitat specialists. Patterns of PCSA across the forelimb were similar between T. indicus and Equus, with the notable exceptions of the biceps brachii and flexor carpi ulnaris, which were much larger in Equus. The differences observed in PCSA between the tapir and horse forelimb muscles highlight muscles that are essential for maintaining stability in the monodactyl limb while moving at high speeds. This quantitative dataset of muscle architecture in a functionally tetradactyl perissodactyl is a pivotal first step towards reconstructing the locomotor capabilities of extinct, four-toed ancestors of modern perissodactyls, and providing further insights into the equid locomotor transition.
Jordi Marcé-nogué - One of the best experts on this subject based on the ideXlab platform.
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Why ruminating ungulates chew sloppily: Biomechanics discern a phylogenetic pattern.
PloS one, 2019Co-Authors: Zupeng Zhou, Daniela E. Winkler, Josep Fortuny, Thomas M. Kaiser, Jordi Marcé-noguéAbstract:There is considerable debate regarding whether mandibular morphology in ungulates primarily reflects phylogenetic affinities or adaptation to specific diet. In an effort to help resolve this debate, we use three-dimensional finite element analysis (FEA) to assess the biomechanical performance of mandibles in eleven ungulate taxa with well-established but distinct dietary preferences. We found notable differences in the magnitude and the distribution of von Mises stress between Artiodactyla and Perissodactyla, with the latter displaying lower overall stress values. Additionally, within the order Artiodactyla the suborders Ruminantia and Tylopoda showed further distinctive stress patterns. Our data suggest that a strong phylogenetic signal can be detected in biomechanical performance of the ungulate mandible. In general, Perissodactyla have stiffer mandibles than Artiodactyla. This difference is more evident between Perissodactyla and ruminant species. Perissodactyla likely rely more heavily on thoroughly chewing their food upon initial ingestion, which demands higher bite forces and greater stress resistance, while ruminants shift comminution to a later state (rumination) where less mechanical effort is required by the jaw to obtain sufficient disintegration. We therefore suggest that ruminants can afford to chew sloppily regardless of ingesta, while hindgut fermenters cannot. Additionally, our data support a secondary degree of adaptation towards specific diet. We find that mandibular morphologies reflect the masticatory demands of specific ingesta within the orders Artiodactyla and Perissodactyla. Of particular note, stress patterns in the white rhinoceros (C. simum) look more like those of a general grazer than like other rhinoceros' taxa. Similarly, the camelids (Tylopoda) appear to occupy an intermediate position in the stress patterns, which reflects the more ancestral ruminating system of the Tylopoda.
