Use of Hands and Feet of Three-Toed Sloths (Bradypus variegatus) during Climbing and Terrestrial Locomotion

Mendel, Frank C.

doi:10.2307/1381249

Cited by 71 publications

(74 citation statements)

References 6 publications

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“…This enables effective anchoring of the hook-like appadages to the support. Sparse data on Bradypus suggest a similar orientation of the hands and feet in this genus (Mendel 1985b). While anchored to the support, hands and feet are oriented in such a way that the volar pads are oriented towards the support.…”

Section: Specializations Associated With the Suspensory Posture And Lmentioning

confidence: 85%

The Convergent Evolution of Suspensory Posture and Locomotion in Tree Sloths

Nyakatura

2011

J Mammal Evol

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Recent phylogenetic analyses imply a distant relationship and long separated evolution of two-toed sloths (Choloepus) and three-toed sloths (Bradypus). No known fossil sloth is interpreted to have been suspensory. As a consequence, the suspensory posture and locomotion of the extant genera likely evolved convergently in both lineages, forming a new framework for the analysis of functional aspects of the locomotor apparatus of extant tree sloths. The suspensory posture and locomotion has altered functional demands from the phylogenetically plesiomorphic nonsuspensory pronograde situation. Here, anatomical traits that have been argued to be of adaptive significance for quadrupedal suspensory locomotion are reviewed and the evolution of these traits is discussed in light of the new framework. Experimental data are largely limited to Choloepus, but help to deduce functional aspects of the anatomy in Bradypus as well. The most important adaptive traits are hands and feet modified into relatively rigid hooklike appendages, great mobility of all joints proximal to the midcarpal and transverse tarsal joints, relatively long arms with a relatively short scapula, a rounded thorax with a small diameter, a highly mobile sterno-clavicular articulation, and emphasis on powerful flexion in the proximal limb joints via advantageous lever arms. Despite these changes, patterns of limb kinematics remained conservative during the course of evolution in the lineages leading to extant tree sloths, and it is suggested here that this also applies to the pattern of neuromuscular control of limb movements during locomotion. Morphological 'solutions'to altered functional demands posed by inversed orientation of the body differ in the two genera of extant tree sloths, thereby corroborating the proposed diphyly. Convergent evolution in tree sloths may be attributed to functional constraints posed by fossorial adaptations in early Xenarthra that canalized sloths to adopt a suspensory posture and locomotion in the arboreal habitat.

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Section: Specializations Associated With the Suspensory Posture And Lmentioning

confidence: 85%

The Convergent Evolution of Suspensory Posture and Locomotion in Tree Sloths

Nyakatura

2011

J Mammal Evol

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“…An animal is expected to use elbow flexors when they drag their body forward against friction with the ground (figure 1c). We defined this motion as creeping motion, which is typified by sloths [45,46]. Elbow adductors are expected to play little role during this creeping motion, unless the humerus is strongly rotated medially (internally).…”

Section: (A) Specimensmentioning

confidence: 99%

Elbow joint adductor moment arm as an indicator of forelimb posture in extinct quadrupedal tetrapods

Fujiwara

Hutchinson

2012

Proc. R. Soc. B.

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Forelimb posture has been a controversial aspect of reconstructing locomotor behaviour in extinct quadrupedal tetrapods. This is partly owing to the qualitative and subjective nature of typical methods, which focus on bony articulations that are often ambiguous and unvalidated postural indicators. Here we outline a new, quantitatively based forelimb posture index that is applicable to a majority of extant tetrapods. By determining the degree of elbow joint adduction/abduction mobility in several tetrapods, the carpal flexor muscles were determined to also play a role as elbow adductors. Such adduction may play a major role during the stance phase in sprawling postures. This role is different from those of upright/sagittal and sloth-like creeping postures, which, respectively, depend more on elbow extensors and flexors. Our measurements of elbow muscle moment arms in 318 extant tetrapod skeletons (Lissamphibia, Synapsida and Reptilia: 33 major clades and 263 genera) revealed that sprawling, sagittal and creeping tetrapods, respectively, emphasize elbow adductor, extensor and flexor muscles. Furthermore, scansorial and non-scansorial taxa, respectively, emphasize flexors and extensors. Thus, forelimb postures of extinct tetrapods can be qualitatively classified based on our quantitative index. Using this method, we find that Triceratops (Ceratopsidae), Anhanguera (Pterosauria) and desmostylian mammals are categorized as upright/sagittally locomoting taxa.

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“…The two-toed sloth, Choloepus didactylus, is very similar to the arboreal rodents in most features studied; however, the sloth was misclassified as terrestrial due to its rather low manus proportions index scores. Sloth hands display particularly short proximal phalanges and elongate middle phalanges, thus grasping is still facilitated by elongate digits, but through modification of different elements (Mendel, 1985). Sloths are also atypical climbers in that their body is suspended below the limbs (Adam, 1999).…”

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confidence: 99%

Skeletal indicators of locomotor adaptations in living and extinct rodents

Samuels

Valkenburgh

2008

Journal of Morphology

250

479

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Living rodents show great diversity in their locomotor habits, including semiaquatic, arboreal, fossorial, ricochetal, and gliding species from multiple families. To assess the association between limb morphology and locomotor habits, the appendicular skeletons of 65 rodent genera from 16 families were measured. Ecomorphological analyses of various locomotor types revealed consistent differences in postcranial skeletal morphology that relate to functionally important traits. Behaviorally similar taxa showed convergent morphological characters, despite distinct evolutionary histories. Semiaquatic rodents displayed relatively robust bones, enlarged muscular attachments, short femora, and elongate hind feet. Arboreal rodents had relatively elongate humeri and digits, short olecranon processes of the ulnae, and equally proportioned fore and hind limbs. Fossorial rodents showed relatively robust bones, enlarged muscular attachments, short antebrachii and digits, elongate manual claws, and reduced hind limb elements. Ricochetal rodents displayed relatively proximal insertion of muscles, disproportionate limbs, elongate tibiae, and elongate hind feet. Gliding rodents had relatively elongate and gracile bones, short olecranon processes of the ulnae, and equally proportioned fore and hind limbs. The morphological differences observed here can readily be used to discriminate extant rodents with different locomotor strategies. This suggests that the method could be applied to extinct rodents, regardless of ancestry, to accurately infer their locomotor ecologies. When applied to an extinct group of rodents, we found two distinct ecomorphs represented in the beaver family (Castoridae), semiaquatic and semifossorial. There was also a progressive trend toward increased body size and increased aquatic specialization in the giant beaver lineage (Castoroidinae).

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Use of Hands and Feet of Three-Toed Sloths (Bradypus variegatus) during Climbing and Terrestrial Locomotion

Cited by 71 publications

References 6 publications

The Convergent Evolution of Suspensory Posture and Locomotion in Tree Sloths

The Convergent Evolution of Suspensory Posture and Locomotion in Tree Sloths

Elbow joint adductor moment arm as an indicator of forelimb posture in extinct quadrupedal tetrapods

Skeletal indicators of locomotor adaptations in living and extinct rodents

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