Orangutan positional behavior and the nature of arboreal locomotion in Hominoidea

Abstract

The Asian apes, more than any other, are restricted to an arboreal habitat. They are consequently an important model in the interpretation of the morphological commonalities of the apes, which are locomotor features associated with arboreal living. This paper presents a detailed analysis of orangutan positional behavior for all age-sex categories and during a complete range of behavioral contexts, following standardized positional mode descriptions proposed by Hunt et al. ([1996] Primates 37:363-387). This paper shows that orangutan positional behavior is highly complex, representing a diverse spectrum of positional modes. Overall, all orthograde and pronograde suspensory postures are exhibited less frequently in the present study than previously reported. Orthograde suspensory locomotion is also exhibited less often, whereas pronograde and orthograde compressive locomotor modes are observed more frequently. Given the complexity of orangutan positional behavior demonstrated by this study, it is likely that differences in positional behavior between studies reflect differences in the interplay between the complex array of variables, which were shown to influence orangutan positional behavior (Thorpe and Crompton 2005 Am. J. Phys. Anthropol. 127:58-78). With the exception of pronograde suspensory posture and locomotion, orangutan positional behavior is similar to that of the African apes, and in particular, lowland gorillas. This study suggests that it is orthogrady in general, rather than forelimb suspend specifically, that characterizes the positional behavior of hominoids.

Fossil hominin shoulders support an African ape-like last common ancestor of humans and chimpanzees

“…The ancestral hominoid condition is reconstructed to be similar in shape and configuration to Pongo (t 0 ). Pongo shares with Lagothrix a penchant for slow, cautious movements through high forest canopy, including frequent bouts of pronograde suspensory locomotion (59)(60)(61). This similarity suggests that derived "suspensory" postcranial characteristics of Pongo shared with other apes are partially convergent, consistent with evidence from Sivapithecus (16).…”

Orangutans employ unique strategies to control branch flexibility

“…The study took place in the Ketambe Research Station (3°41ЈN, 97°39ЈE) in the Gunung Leuser Ecosystem, Sumatra, comprising pristine rainforest on riverine terraces. Our method is described in detail elsewhere (11,12). In brief, 1-min instantaneous sampling was used during whole-day focal visual observations to collect detailed support-use and behavioral-context data and positional behavior (see Table 2), backed up with video recordings of typical samples of some positional behaviors.…”

“…1). Overall 29% of orangutan locomotion occurred on Ͼ4 supports, and although recording detailed support characteristics when Ͼ4 supports were used was not possible, in many such cases body mass was supported only by handfuls of foliage (11,12). If we take mean values as a broad indication of preference, then our results suggest that orangutans demonstrate a preference for single supports with a SS not much smaller than 6 cm and multiple supports with a SS not much smaller than 3.5 cm per support.…”

Functional Anatomy and Adaptation of Male Gorillas (Gorilla gorilla gorilla) With Comparison to Male Orangutans (Pongo pygmaeus)

“…Their limbs can be recruited to act in nonstereotyped positions relative to the body and to each other (Cant, 1992;Povinelli and Cant, 1995). Joint flexibility is crucial to the variety of postures and modes in feeding, nesting, and moving in trees, including vertically climbing, and suspending (Sugardjito and van Hooff, 1986;Cant, 1987;Thorpe and Crompton, 2006). Pronounced rotational capabilities in the shoulder, wrist, hip, and knee joints facilitate clambering movements (Morbeck and Zihlman, 1988;Tuttle and Cortright, 1988) and are well suited to maneuvering across arboreal pathways and crossing gaps.…”

“…Using their bulk, they sway branches and form bridges to adjacent trees, and use their long and powerful arms and hands to pull in flexible branches to cross gaps. They recruit their prehensile feet to grasp nearby branches and propel themselves through the canopy (Chevalier-Skolnikoff et al, 1982;Sugardjito, 1982;Cant, 1987Cant, , 1992Thorpe and Crompton, 2006). Their cognitive skills assist in assessing the biomechanics of branch flexibility and in assuming the most effective body positions to make their way through the canopy (Povinelli and Cant, 1995).…”