Architectural Properties of Sloth Forelimb Muscles (Pilosa: Bradypodidae)

Olson, Rachel A.; Glenn, Z. D.; Cliffe, Rebecca N.; Butcher, Michael T.

doi:10.1007/s10914-017-9411-z

Cited by 32 publications

(81 citation statements)

References 45 publications

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“…Positional data on free‐ranging Bradypus variegatus in Venezuela demonstrated that three‐toed sloths actually shared their locomotion between vertical climbing and under‐branch suspensory locomotion, whereas above‐branch sitting postures largely dominated over below‐branch hanging (Urbani & Bosque, ). These findings partly support previous predictions and may actually account for the observed differences between three‐ and two‐toed sloths (Mendel, , ) that are translated in some morphological divergences (Grand, ; Miller, ; Nyakatura & Fischer, , ; Olson, Glenn, Cliffe, & Butcher, ). Therefore, comparable data on unrestrained locomotion and postures of two‐toed sloths in a naturalistic setting would further contribute to the understanding of these morphological and behavioral differences and provide valuable information on the adaptive and evolutionary significance of suspensory arboreality.…”

Section: Introductionsupporting

confidence: 88%

A suspensory way of life: Integrating locomotion, postures, limb movements, and forces in two‐toed sloths Choloepus didactylus (Megalonychidae, Folivora, Pilosa)

et al. 2018

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Over the last decade, we have learned much about the anatomy, evolutionary history, and biomechanics of the extant sloths. However, most of this study has involved studying sloths in controlled conditions, and few studies have explored how these animals are behaving in a naturalistic setting. In this study, we integrate positional activities in naturalistic conditions with kinematic and kinetic observations collected on a simulated runway to best capture the biomechanical behavior of Linnaeus's two-toed sloths. We confirm that the dominant positional behaviors consist of hanging below the support using a combination of forelimbs and hindlimbs, and walking quadrupedally below the branches. The majority of these behaviors occur on horizontal substrates that are approximately 5-10 cm in diameter. The kinematics of suspensory walking observed both in the naturalistic settings and on simulated arboreal runways are dominated by movement of the proximal limb elements, while distal limb elements tend to show little excursion. Joint kinematics are similar between the naturalistic setting and the simulated runway, but movements of the shoulder and hip tend to be exaggerated while moving in simulated conditions. Kinetic patterns of the two-toed sloth can be explained almost entirely by considering them as an inverted linked strut. However, medially directed forces toward the substrate were more frequent than expected in the forelimb, which may help sloths maintain a better "grip" on the substrate. This study serves as a model of how to gain a comprehensive understanding of the functional-adaptive profile of a particular species.

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Section: Introductionsupporting

confidence: 88%

A suspensory way of life: Integrating locomotion, postures, limb movements, and forces in two‐toed sloths Choloepus didactylus (Megalonychidae, Folivora, Pilosa)

et al. 2018

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“…As equids are much larger than juvenile tapirs, direct comparison of muscle mass was considered unsuitable. Ontogenetic studies of mammalian and avian muscle and tendon anatomy suggest that limb muscles can scale both allometrically and isometrically through ontogeny, dependent upon the muscle and the taxon (Miller et al 2008;Olson et al 2018;Martin et al 2019). Unfortunately, no data is presently available for ontogenetic variation or scaling in muscle architecture for perissodactyls, and therefore scaling of juvenile Tapirus data to an adult size was not performed.…”

Section: Statistical Comparisonsmentioning

confidence: 99%

“…isometric vs. allometric scaling in different muscles; Miller et al 2008) precluded us from pursuing this as an option. Encouragingly, the limited number of previous studies investigating ontogenetic variation in architecture of mammalian limb muscles have shown that, although absolute values do differ, the patterns of PCSA across forelimb muscles do not vary greatly between adults and juveniles (Olson et al 2018). Therefore, for the comparisons presented in this study, we believe that the juvenile tapir offers a viable approximation of the pattern of muscular architecture that may be observed in an adult of the same species.…”

Section: Forelimb Muscle Similarities Between Tapirus and Equusmentioning

confidence: 99%

“…With regard to locomotion, the size of skeletal muscles and the arrangement of fascicles within them can be used to identify the potential velocity and power of muscle contractions (Olson et al. ); greater mass of proximal muscles relative to distal muscles can indicate reduced distal inertia during swing phase of running, affecting the kinematics of the animal (Wickler et al. ); and comparing PCSA between homologous muscles in different species can highlight differences in maximum force‐generating capacity (Payne et al.…”

Section: Introductionmentioning

confidence: 99%

“…As a result, the muscular arrangements and physiological cross-sectional areas (PCSA), both critical inputs for modelling skeletal processes such as feeding and locomotion, can only be estimated based on available phylogenetic bracketing (Witmer, 1995). With regard to locomotion, the size of skeletal muscles and the arrangement of fascicles within them can be used to identify the potential velocity and power of muscle contractions (Olson et al 2018); greater mass of proximal muscles relative to distal muscles can indicate reduced distal inertia during swing phase of running, affecting the kinematics of the animal (Wickler et al 2004); and comparing PCSA between homologous muscles in different species can highlight differences in maximum force-generating capacity ). All these properties can aid in predicting maximum force and power muscles can generate, which are essential for musculoskeletal models examining changes in locomotor abilities (e.g.…”

Section: Introductionmentioning

confidence: 99%

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Comparative forelimb myology and muscular architecture of a juvenile Malayan tapir (Tapirus indicus)

Maclaren

McHorse

2019

Journal of Anatomy

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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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Evolutionary adaptations in the flexor digitorum profundus muscle in Tamandua mexicana (Xenarthra, Myrmecophagidae)

García

Arbeláez-Quiñones

Montealegre-Hurtado

2020

The Anatomical Record

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The northern tamandua (Tamandua mexicana) is a neotropical mammal of the order Pilosa, suborder Vermilingua, and family Myrmecophagidae. This species has anatomical and functional adaptations in its forelimb for semiarboreal quadrupedal locomotion. Several studies have reported that the medial head of the triceps brachii and flexor digitorum profundus muscles are fused in species belonging to the family Myrmecophagidae. However, there is no reference to the innervation in these. The triceps brachii muscle is commonly innervated by the radial nerve and the flexor digitorum profundus muscle by the ulnar and median nerves. This study aims to describe the gross anatomy of the flexor digitorum profundus muscle in Tamandua mexicana with respect to the shape, origin, insertion, innervation, and arterial supply. Both forelimbs of nine specimens were used, which were dissected from superficial to deep layers. The formalin‐fixed caudomedial forearm muscles were weighed, and the weight percentages of individual forearm muscle specimens were calculated. The flexor digitorum profundus had the highest weight among the forearm muscles and consisted of five heads (three humerals, one radial, and one ulnar). These heads were innervated by median and ulnar nerves; therefore, based on the innervation pattern, we concluded that the medial head of the triceps brachii muscle is not fused with the flexor digitorum profundus. Therefore, the flexor digitorum profundus muscle is highly developed in Tamandua and occupies the caudal part of the arm and forearm, which is an evolutionary adaptation that could have occurred during evolution from the common ancestor of Tamandua and Myrmecophaga.

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Architectural Properties of Sloth Forelimb Muscles (Pilosa: Bradypodidae)

Cited by 32 publications

References 45 publications

A suspensory way of life: Integrating locomotion, postures, limb movements, and forces in two‐toed sloths Choloepus didactylus (Megalonychidae, Folivora, Pilosa)

A suspensory way of life: Integrating locomotion, postures, limb movements, and forces in two‐toed sloths Choloepus didactylus (Megalonychidae, Folivora, Pilosa)

Comparative forelimb myology and muscular architecture of a juvenile Malayan tapir (Tapirus indicus)

Evolutionary adaptations in the flexor digitorum profundus muscle in Tamandua mexicana (Xenarthra, Myrmecophagidae)

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