Functional Adaptations in the Forelimb of the Sloths

Miller, Ruth A.

doi:10.2307/1374529

Cited by 49 publications

(71 citation statements)

References 7 publications

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“…In Bradypus, the neck is weakly muscled, and the clavicle is absent in adults (15). However, we have observed rudimentary clavicles in all of our Bradypus specimens that do not yet show ossification of middle neck centra (Fig.…”

Section: Skeletogenesis In Armadillosmentioning

confidence: 62%

Skeletal development in sloths and the evolution of mammalian vertebral patterning

Hautier

Weisbecker

Sánchez‐Villagra

et al. 2010

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

126

149

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Mammals show a very low level of variation in vertebral count, particularly in the neck. Phenotypes exhibited at various stages during the development of the axial skeleton may play a key role in testing mechanisms recently proposed to explain this conservatism. Here, we provide osteogenetic data that identify developmental criteria with which to recognize cervical vs. noncervical vertebrae in mammals. Except for sloths, all mammals show the late ossification of the caudal-most centra in the neck after other centra and neural arches. In sloths with 8–10 ribless neck vertebrae, the caudal-most neck centra ossify early, matching the pattern observed in cranial thoracic vertebrae of other mammals. Accordingly, we interpret the ribless neck vertebrae of three-toed sloths caudal to V7 as thoracic based on our developmental criterion. Applied to the unusual vertebral phenotype of long-necked sloths, these data support the interpretation that elements of the axial skeleton with origins from distinct mesodermal tissues have repatterned over the course of evolution.

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Section: Skeletogenesis In Armadillosmentioning

confidence: 62%

Skeletal development in sloths and the evolution of mammalian vertebral patterning

Hautier

Weisbecker

Sánchez‐Villagra

et al. 2010

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

126

149

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“…Le Gros Clark (1924), Davis (1938), and Verma (1965) regarded the m. spinodeltoideus as the m. teres minor. Carlsson (1922) and Miller (1935) noted the absence of this muscle in the genus Tupaia. Most probably, all these authors failed to dissect the m. teres minor from the m. infraspinatus.…”

Section: Intrinsic Musculature Of Shoulder Jointmentioning

confidence: 97%

“…coracobrachiales) characteristic of mammals. Miller (1935) mentions the presence of the third coracobrachial muscle in Tupaia picta but does not describe it.…”

Section: This Muscle Contributes Very Little To the Supination Of Thementioning

confidence: 99%

“…The two bands (heads) fuse together and insert by an aponeurosis on the medial and posterior sur- faces of the olecranon. According to Miller (1935) this muscle has only one origin and it is associated with the m. teres major. George (1977) has found the second head originating from pars spinohumeralis (see above) but not from the m. latissimus dorsi in the narrow sense.…”

Section: Posterior Group Of Musclesmentioning

confidence: 99%

See 1 more Smart Citation

Forelimb Morphology of Tree Shrews

Panyutina

Korzun

Kuznetsov

2015

Flight of Mammals: From Terrestrial Limbs to Wings

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“…As with sloths, pottos move on the lower surface of branches but also commonly use the upper surfaces and are able to rotate or spiral around the branches [Walker, 1969;Oates, 1984;Nekaris, 2013]. This maneuverability contrasts with the predominantly suspensory locomotion on the underside of branches of sloths [Miller, 1935;Nyakatura, 2012], and requires a 13 more three-dimensional visual sampling across different angles of the branches for which a more concentric organization of retinal ganglion cells is useful. Among primates, the presence of a well-developed fovea is a distinctive feature.…”

Section: Unlike Sloths Pottos Have a Concentric Topographic Distribumentioning

confidence: 99%

The Topographic Organization of Retinal Ganglion Cell Density and Spatial Resolving Power in an Unusual Arboreal and Slow-Moving Strepsirhine Primate, the Potto <b><i>(Perodicticus potto)</i></b>

Coimbra¹,

Kaswera‐Kyamakya

Gilissen³

et al. 2016

Brain Behav Evol

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The potto (Perodicticus potto) is an arboreal strepsirhine found in the rainforests of central Africa. In contrast to most primates, the potto shows slow-moving locomotion over the upper surface of branches, where it forages for exudates and crawling invertebrates with its head held very close to the substrate. Here, we asked whether the retina of the potto displays topographic specializations in neuronal density that correlate with its unusual lifestyle. Using stereology and retinal wholemounts, we measured the total number and topographic distribution of retinal ganglion cells (total and presumed parasol), as well as estimating the upper limits of the spatial resolution of the potto eye. We estimated ∼210,000 retinal ganglion cells, of which ∼7% (∼14,000) comprise presumed parasol ganglion cells. The topographic distribution of both total and parasol ganglion cells reveals a concentric centroperipheral organization with a nasoventral asymmetry. Combined with the upwardly shifted orbits of the potto, this nasoventral increase in parasol ganglion cell density enhances contrast sensitivity and motion detection skywards, which potentially assists with the detection of predators in the high canopy. The central area of the potto occurs ∼2.5 mm temporal to the optic disc and contains a maximum ganglion cell density of ∼4,300 cells/mm². We found no anatomical evidence of a fovea within this region. Using maximum ganglion cell density and eye size (∼14 mm), we estimated upper limits of spatial resolving power between 4.1 and 4.4 cycles/degree. Despite their reported reliance on olfaction to detect exudates, this level of spatial resolution potentially assists pottos with foraging for small invertebrates and in the detection of predators.

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Functional Adaptations in the Forelimb of the Sloths

Cited by 49 publications

References 7 publications

Skeletal development in sloths and the evolution of mammalian vertebral patterning

Skeletal development in sloths and the evolution of mammalian vertebral patterning

Forelimb Morphology of Tree Shrews

The Topographic Organization of Retinal Ganglion Cell Density and Spatial Resolving Power in an Unusual Arboreal and Slow-Moving Strepsirhine Primate, the Potto <b><i>(Perodicticus potto)</i></b>

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