Use of Hands and Feet of Two-Toed Sloths (Choloepus hoffmanni) during Climbing and Terrestrial Locomotion

Mendel, Frank C.

doi:10.2307/1380728

Cited by 56 publications

(67 citation statements)

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“…In both sloths and lorisids, the shortening of these lever arms in conjunction with the reduction of trunk extensor muscle mass indicates a reduced reliance on powerful extension of the spine (Grand, 1977(Grand, , 1978. This is consistent with the fact that sloths and lorisids have well-developed trunk flexor muscles (Britton, 1941;Grand, 1977Grand, , 1978, and both (especially sloths) frequently engage in inverted suspensory postures by all four limbs in which the trunk typically remains flexed and active back extension is not required (Walker, 1974;Gebo, 1987;Jouffroy, 1989;Jouffroy and Petter, 1990;Mendel, 1981Mendel, , 1985aCurtis, 1995). Likewise, the relatively short spinous processes of Pongo are consistent with this hominoid's emphasis on suspensory behaviors (Sugardjito, 1982).…”

Section: Palaeopropithecussupporting

confidence: 71%

Morphometric analysis of lumbar vertebrae in extinct Malagasy strepsirrhines

Shapiro

Seiffert

Godfrey

et al. 2005

American J Phys Anthropol

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Previous research on subfossil lemurs has revealed much about the positional behavior of these extinct strepsirrhines, but a thorough quantitative analysis of their vertebral form and function has not been performed. In this study, 156 lumbar vertebrae of Pachylemur, Archaeolemur, Megaladapis, Mesopropithecus, Babakotia, and Palaeopropithecus (11 species in all) were compared to those of 26 species of extant strepsirrhines and haplorhines. Lumbar shape was compared among species, using a principal components analysis (PCA) in conjunction with selected vertebral indices. The first principal component revealed strong separation between Palaeopropithecus at one extreme, and Archaeolemur/Pachylemur at the other, with Babakotia, Mesopropithecus, and Megaladapis in an intermediate position. Palaeopropithecus has markedly shorter spinous processes and wider laminae than do the other subfossil taxa, consistent with sloth-like, inverted suspensory postures. The moderately reduced lumbar spinous processes of Babakotia, Mesopropithecus, and Megaladapis are convergent with those of lorisids and Pongo, reflecting antipronogrady, but a less specialized adaptation than that of Palaeopropithecus. Archaeolemur and Pachylemur share relatively elongated spinous processes, in conjunction with other features (e.g., transverse process orientation and relatively short vertebral bodies) indicative of pronograde, quadrupedal locomotion characterized by reduced agility. All subfossil taxa exhibit adaptations emphasizing lumbar spinal stability (e.g., relatively short vertebral bodies, and transverse processes that are not oriented ventrally); we believe this probably reflects convergent mechanical demands connected to large body size, irrespective of specific locomotor mode. Reconstructions of positional behavior in subfossil lemurs based on lumbar vertebrae are largely consistent with those based on other aspects of the postcrania.

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Section: Palaeopropithecussupporting

confidence: 71%

Morphometric analysis of lumbar vertebrae in extinct Malagasy strepsirrhines

Shapiro

Seiffert

Godfrey

et al. 2005

American J Phys Anthropol

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“…In arboreal and digging mammals, e.g., in Grant's Golden Mole (31) and in certain extinct taxa of sloths (32), this evolutionary challenge has been circumvented differently, by condensing phalangeal elements in normal proportions but then fusing phalanges with one another or with the metapodial to produce a long segment from shorter phalanges. Other arboreal mammals, such as the Two-Toed Sloth (33,34), have paralleled the digging/perching/predatory birds in extending their distal phalanges to a greater extent than the proximal ones. An insight into at least a potential mechanism by which this extension might have occurred comes from a study (15) in which Fgf signaling was maintained experimentally at the distal tip of a growing digit ray.…”

Section: Innovation In the Evolution Of The Distal Phalanges In Derivmentioning

confidence: 99%

Developmental bias in the evolution of phalanges

Kavanagh

Shoval

Winslow

et al. 2013

Proc. Natl. Acad. Sci. U.S.A.

119

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Evolutionary theory has long argued that the entrenched rules of development constrain the range of variations in a given form, but few empirical examples are known. Here we provide evidence for a very deeply conserved skeletal module constraining the morphology of the phalanges within a digit. We measured the sizes of phalanges within populations of two bird species and found that successive phalanges within a digit exhibit predictable relative proportions, whether those phalanges are nearly equal in size or exhibit a more striking gradient in size from large to small. Experimental perturbations during early stages of digit formation demonstrate that the sizes of the phalanges within a digit are regulated as a system rather than individually. However, the sizes of the phalanges are independent of the metatarsals. Temporal studies indicate that the relative sizes of the phalanges are established at the time of initial cell condensation. Measurements of phalanges across species from six major taxonomic lineages showed that the same predictable range of variants is conserved across vast taxonomic diversity and evolutionary time, starting with the very origins of tetrapods. Although in general phalangeal variations fall within a range of nearly equal-sized phalanges to those following a steep large-to-small gradient, a novel derived condition of excessive elongation of the distal-most phalanges has evolved convergently in multiple lineages, for example under selection for grasping rather than walking or swimming. Even in the context of this exception, phalangeal variations observed in nature are a small subset of potential morphospace.developmental module | developmental constraint | phalanx

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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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Use of Hands and Feet of Two-Toed Sloths (Choloepus hoffmanni) during Climbing and Terrestrial Locomotion

Cited by 56 publications

References 0 publications

Morphometric analysis of lumbar vertebrae in extinct Malagasy strepsirrhines

Morphometric analysis of lumbar vertebrae in extinct Malagasy strepsirrhines

Developmental bias in the evolution of phalanges

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

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