An anatomical and mechanical analysis of the douc monkey (genus Pygathrix), and its role in understanding the evolution of brachiation

Abstract

The adoption of arm-swinging represents a major shift within at least three anthropoid clades and little data exist about its transition. Across species, few mechanical differences are observed during arm-swinging. Apparently, there are limited functional solutions to the challenges associated with moving bimanually below branches, especially in more proximal forelimb regions. Morphological data support this idea that the Pygathrix distal forelimb differs from apes more than its proximal end. These results can inform other studies of ape evolution, the pronograde to orthograde transition, and the convergent ways in which suspensory locomotion evolved in primates.

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

“…This profile establishes two‐toed sloths as the most suspensory arboreal mammals so far. Arboreal forelimb suspensory primates, such as the orangutans (Cant, ; Thorpe & Crompton, ), the gibbons and siamangs (Byron & Covert, ; Cannon & Leighton, ; Fleagle, ; Wright, Stevens, Covert, & Nadler, ), the odd‐nosed colobines (Byron & Covert, ; Byron, Granatosky, & Covert, ; Wright et al, ), and the spider monkeys (Youlatos, ), never engage in such high rates of fore‐ and hindlimb hanging. Two‐toed sloths are even more suspensory than three‐toed sloths ( Bradypus variegatus ), which also use suspension for 92% of locomotor bouts and, as low as 33%, of postural bouts (Urbani & Bosque, ).…”

“…This profile establishes two-toed sloths as the most suspensory arboreal mammals so far. Arboreal forelimb suspensory primates, such as the orangutans (Cant, 1987;Thorpe & Crompton, 2006), the gibbons and siamangs (Byron & Covert, 2004;Cannon & Leighton, 1994;Fleagle, 1976;Wright, Stevens, Covert, & Nadler, 2008), the oddnosed colobines (Byron & Covert, 2004;Byron, Granatosky, & Covert, 2017;Wright et al, 2008), and the spider monkeys (Youlatos, 2008), never engage in such high rates of fore-and hindlimb hanging.…”

“…Additionally, the circular thorax, the ligamentous connection between the clavicle and the sternum, the comparably small scapula, the shallow glenoid fossa, and the relatively rounded humeral head appear to facilitate the extensive mobility of the pectoral girdle (Miller, 1935;Nyakatura & Fischer, 2010b). At the level of the elbow, the reduced olecranon also seems to favor the wide range of necessary movements (Byron et al, 2017;Mendel, 1981aMendel, , 1981c. Furthermore, the midcarpal joints are shaped and arranged so as to enable a wide range of movements, from complete extension to great rates of rotatory mobility (Jenkins, 1981;Mendel, 1979Mendel, , 1981aMendel, , 1981c.…”

Comparison of spatiotemporal gait characteristics between vertical climbing and horizontal walking in primates

“…steady-state locomotion) throughout the climbing or walking trial, in which a full forelimb and/or hindlimb contacted the pole, and which exhibited a symmetric footfall sequence were retained for analysis. For all data, steady-state locomotion was determined by a combination of video, force and symmetry data following previously established methods (Byron et al, 2017;Granatosky et al, 2016aGranatosky et al, , 2018aHanna et al, 2017). For all trials, symmetry was determined using the methods of Cartmill et al (2002), with a ±10 criterion such that the timing of opposite limb touchdown could vary between 40 and 60% of the stride cycle (50% indicates the timing of opposing limbs is exactly 1/2 of the cycle).…”

Hominoidea Locomotion

“…During below-branch quadrupedal locomotion, the torso is pronograde (parallel to the ground) with both the forelimbs and hindlimbs used to hang beneath the substrate (the tree branch) and bear the body weight, loading the limbs in tension Stern 1975). Diagonal-sequence gait patterns (hindlimb followed by contralateral forelimb) are utilized and the forelimbs are the dominant weight bearing limbs, suggesting that this locomotor form may be a mechanical intermediate transition to another suspensory locomotor mode known as arm-swinging (Byron et al 2017;.…”