Limb kinematics during locomotion in the two-toed sloth (Choloepus didactylus, Xenarthra) and its implications for the evolution of the sloth locomotor apparatus

Nyakatura, John A.; Petrovitch, A.; Fischer, Martin S.

doi:10.1016/j.zool.2009.11.003

Cited by 55 publications

(89 citation statements)

References 76 publications

(112 reference statements)

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“…These inferences were based on previous works on extant Pilosa (Taylor, 1978(Taylor, , 1985Mendel, 1979Mendel, , 1981Mendel, , 1985Nyakatura et al, 2010) and other mammals (Argot, 2001;Szalay and Sargis, 2001;Sargis, 2002;Candela and Picasso, 2008), and mechanical analogues when needed. The interface between function and biological role was the averaged biomechanical situation (Oxnard, 1984), which integrates functional information of each feature and element in a mechanical profile.…”

Section: Methodsmentioning

confidence: 99%

Muscular Reconstruction and Functional Morphology of the Forelimb of Early Miocene Sloths (Xenarthra, Folivora) of Patagonia

Toledo

Bargo

Vizcaı́no

2012

The Anatomical Record

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Early Miocene sloths are represented by a diversity of forms ranging from 38 to 95 kg, being registered mainly from Santacrucian Age deposits in southern-most shores of Patagonia, Argentina. Their postcranial skeleton differs markedly in shape from those of their closest living relatives (arboreal forms of less than 10 kg), Bradypus and Choloepus. In order to gain insight on functional properties of the Santacrucian sloths forelimb, musculature was reconstructed and a comparative, qualitative morphofunctional analysis was performed, allowing proposing hypotheses about biological role of the limb in substrate preferences, and locomotor strategies. The anatomy of the forelimb of Santacrucian sloths resembles more closely extant anteaters such as Tamandua and Myrmecophaga, due to the robustness of the elements, development of features related to attachment of ligaments and muscles, and conservative, pentadactylous, and strong-clawed manus. The reconstructed forelimb musculature was very well developed and resembles that of extant Pilosa (especially anteaters), although retaining the basic muscular configuration of generalized mammals. This musculature allowed application of powerful forces, especially in adduction of the forelimb, flexion and extension of the antebrachium, and manual prehension. These functional properties are congruent with both climbing and digging activities, and provide support for proposed Santacrucian sloths as good climbing mammals, possibly arboreal or semiarboreal, being also capable diggers. Their climbing strategies were limited, thus these forms relied mainly on great muscular strength and curved claws of the manus to move cautiously on branches. Anat Rec, 296:305-325,

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Section: Methodsmentioning

confidence: 99%

Muscular Reconstruction and Functional Morphology of the Forelimb of Early Miocene Sloths (Xenarthra, Folivora) of Patagonia

Toledo

Bargo

Vizcaı́no

2012

The Anatomical Record

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“…Nyakatura et al (2010) found that during almost the complete contact phase of a stride both manus and pes of Choloepus are held approximately perpendicular to the superstrate. This enables effective anchoring of the hook-like appadages to the support.…”

Section: Specializations Associated With the Suspensory Posture And Lmentioning

confidence: 98%

“…While anchored to the support, hands and feet are oriented in such a way that the volar pads are oriented towards the support. As a consequence, the direction of motion in the metatarsophalangeal and metacarpo-phalangeal joints is rotated out of the parasagittal plane into the transverse body plane and can no longer contribute to progression in sloths (see detailed discussion in Nyakatura et al 2010). Thus, the unit of tarsus and metatarsus cannot be considered an individual functional element of the hindlimb sensu Kuznetsov (1985) and Fischer (1994) as is characteristic for mammals.…”

Section: Specializations Associated With the Suspensory Posture And Lmentioning

confidence: 99%

“…For example, anatomical and behavioral studies suggest that Bradypus has better vision than Choloepus (Mendel et al 1985;Piggins and Muntz 1985). Indeed, while Bradypus may be able to see its route for some distance (Piggins and Muntz 1985), Choloepus often seems to rely on its olfactory sense to explore its support, and engages in an 'exploratory gait' (Nyakatura et al 2010). However, direct data on the locomotion of Choloepus and Bradypus have been limited to two studies describing general characteristics in both genera (Mendel 1981c(Mendel , 1985b and two experimental studies focused on potential use of the hands and feet relative to support size (Mendel 1981a, b).…”

Section: Analysis Of Locomotionmentioning

confidence: 99%

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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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“…It is not surprising that intralimb coordination is also consistent among small to medium-sized therian mammals, ranging across marsupials, primates, carnivores, artiodactyls, rodents and hyraxes (e.g. Fischer et al, 2002;Jenkins, 1971;Jenkins, 1974;Jenkins and Camazine, 1977;Jenkins and Weijs, 1979;Rocha-Barbosa et al, 2005;Schmidt, 2005;Schmidt, 2008;Schmitt, 1999), and can even be recognized in the suspensory locomotion of sloths (Nyakatura et al, 2010). General demands for coping with terrestrial substrates (amongst others) are behaviors that simplify control, particularly at high velocities and at touch-down, when errors in position are most likely (Gatesy and Biewener, 1991), thereby explaining some of the interspecific consistency of parameters.…”

Section: Conserved Pattern Of Intralimb Coordination In Fore-aft Motimentioning

confidence: 98%

Comparative intralimb coordination in avian bipedal locomotion

Stoessel

Fischer

2012

Journal of Experimental Biology

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SUMMARYAnalyses of how intralimb coordination during locomotion varies within and across different taxa are necessary for understanding the morphological and neurological basis for locomotion in general. Previous findings suggest that intralimb proportions are the major source of kinematic variation that governs intralimb coordination across taxa. Also, independence of kinematics from habitat preference and phylogenetic position has been suggested for mammals. This leads to the hypothesis that among equally sized bird species exhibiting equal limb proportions, similar kinematics can be observed. To test this hypothesis, the bipedal locomotion of two distantly related ground-dwelling bird species (Eudromia elegans and Coturnix coturnix) and of a less terrestrial species (Corvus monedula) was investigated by means of a biplanar high-speed X-ray videographic analysis. Birds exhibited similar intralimb proportions and were filmed over a broad range of speed while moving on a treadmill. Joint and limb element angles, as well as pelvic rotations, were quantified. Regarding fore-aft motions of the limb joints and elements, a congruent pattern of intralimb coordination was observed among all experimental species. The sample of species suggests that this is largely independent of their habitat preference and systematic position and seems to be related to demands for coping with an irregular terrain with a minimum of necessary control. Hence, the initial hypothesis was confirmed. However, this congruence is not found when looking at medio-lateral limb motions and pelvic rotations, showing distinct differences between grounddwellers (e.g. largely restricted to a parasagittal plane) and C. monedula (e.g. increased mobility of the hip joint). Supplementary material available online at

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Limb kinematics during locomotion in the two-toed sloth (Choloepus didactylus, Xenarthra) and its implications for the evolution of the sloth locomotor apparatus

Cited by 55 publications

References 76 publications

Muscular Reconstruction and Functional Morphology of the Forelimb of Early Miocene Sloths (Xenarthra, Folivora) of Patagonia

Muscular Reconstruction and Functional Morphology of the Forelimb of Early Miocene Sloths (Xenarthra, Folivora) of Patagonia

The Convergent Evolution of Suspensory Posture and Locomotion in Tree Sloths

Comparative intralimb coordination in avian bipedal locomotion

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