The body center of mass in primates: Is it more caudal than in other quadrupedal mammals?

Abstract

Objectives: Whole body center of mass (BCoM) position values are lacking for a comparative sample of primates. Therefore, it still remains unknown whether the BCoM in primates is more posteriorly located than in other mammals. The aim of the present report is to provide data for a large sample of primate species and to compare the position of the BCoM in primates to non-primate mammals. Materials and methods:We collected morphometrics on eight primate species belonging to various families: Hylobatidae (Nomascus grabriellae, Nomascus Siki), Cercopithecidae (Cercopithecus roloway, Cercopithecus lhoesti, Colobus guereza, Trachypithecus francoisi), Cebidae (Sapajus xanthosternos), and Atelidae (Ateles fusciceps). Using a geometric model, we assessed the position of the BCoM in a natural quadrupedal posture and in a control posture. To complete our comparative sample with a wider range of morphotypes, we added the data available in the literature for hominoids (Pan paniscus, Pan troglodytes, Gorilla gorilla, Pongo pygmaeus, Hylobates lar) and another cercopithecoid species (Papio anubis). We also evaluated the phylogenetic signal of the position of the BCoM in primates.Results: The variation in the position of the BCoM in primates is very large, ranging from 40% of the distance between the hip and the shoulder in Ateles fusciceps to 63% in Hylobates lar. We observed a strong phylogenetic signal for this trait: hominoid species, as well as the baboon, have a cranial BCoM relative to the midline between the hip and the shoulder, arboreal cercopithecoids and the spider monkey have a caudal BCoM, and the capuchin monkey has a BCoM positioned at mid-trunk. The variation observed in non-primate quadrupedal mammals lies inside the variation range of primates, from 51% in Felis catus to 63% in Canis familiaris.Discussion: The BCoM of primates is not more posteriorly located than in other quadrupedal mammals; however, there is a substantial range of variation in primates, from caudal (in arboreal quadrupeds) to cranial (in hominoids and terrestrial quadrupeds) positions. This variation is related to a phylogenetic model that suggests stabilizing selection for this trait. It seems that the BCoM position mostly depends of the size of the appendicular system (i.e., limbs) and the tail.Therefore, it may also reflect a general trend in quadrupedal mammals with arboreal species exhibiting a caudal BCoM and terrestrial species exhibiting a cranial BCoM. These results are discussed in the context of the locomotor evolution of primates including locomotor habits and gait mechanics. We also propose a new "passive" mechanism for the explanation of the particular weight support pattern observed in primates with tails.

Trabecular bone variation in the gorilla calcaneus

“…The relatively thicker trabeculae and higher bone volume fraction in the anterior calcaneus likely serve as an adaptation to (potentially) relatively higher forces associated with gorilla body mass, consistent with our predictions (and findings from Giddings et al, 2000). This anterior-posterior difference is likely exacerbated in gorillas because of their anteriorly positioned center of mass (Druelle et al, 2019) talar facet, the sustentaculum tali, the superior cuboid facet, and within the calcaneal tuberosity (DeMars et al, 2021). While there is a similar trend of high BV/TV below the posterior talar facet, sustentaculum tali, and cuboid facet in gorillas, relatively high BV/TV in the calcaneal tuberosity is not observed in any of the gorilla taxa, indicating that the trabecular pattern in humans may be indicative of a bipedal gait.…”

The quadrupedal walking gait of the olive baboon, Papio anubis: an exploratory study integrating kinematics and EMG

“…For example, a body centre of mass located at mid-trunk coupled to a forelimb that lags behind the hindlimb by 25% would result in a flat trajectory of the BCoM (Griffin et al 2004). Baboons have a BCoM positioned at mid-trunk compared to dogs that have a cranially positioned BCoM (Druelle et al 2019), hence baboons may rely on limb phase only to produce "optimal" fluctuations of their BCoM. In the present study, we found that the ipsilateral forelimb lagged behind the hindlimb by 61% in average (min: 54%, max: 69%) and there is a significant relationship between the recovery rates and the limb phase (i.e.…”

“…During primate quadrupedal walking, distal limb muscles are suggested to be under higher cortical control including different speed-related modulations of the limbs compared to other quadrupedal mammals (Courtine et al 2005). The different inertial properties of non-human primates compared to other quadrupeds Druelle et al 2019) should also affect the way the work is performed, and the forces transmitted. Overall, more flexible capabilities of the neuromotor control are suggested in primates (Courtine et al 2005;Jungers & Anapol 1985;Shapiro et al 1997) with the hand and the foot having distinct functional roles (Druelle et al 2018;Hashimoto et al 2011;Lawler 2006;Patel et al 2015).…”

The gaits of marsupials and the evolution of diagonal‐sequence walking in primates

“…More recent authors (Kimura, Okada, & Ishida, ; Rollinson & Martin, ; Tomita, ) have advanced just the opposite argument—that primates have unusually big, strong hind limbs; that this produces a caudal shift in the animals' center of mass; that a primate walking with a DC gait therefore tends to pitch backward at the moment of forefoot touchdown (whereas other animals tend to pitch forward); and that the contralateral hindfoot in the diagonal pair is set down earlier to prevent this, thus producing a DS gait. Subsequent studies have not borne out this idea (Cartmill, Cartmill, Schmitt, & Lemelin, ; Druelle, Berthet, & Quintard, ; Vilensky & Larson, ; Young, Patel, & Stevens, ). Prost () argued that the DC‐DS pattern, but not the DC‐LS pattern, “allows an animal to use lateral spine bending to increase distance between successive contact points for the same leg,” thus increasing stride length.…”