Adjustments of Limb Mechanics in Cotton-top Tamarins to Moderate and Steep Support Orientations: Significance for the Understanding of Early Primate Evolution

Effects of Substrate Size and Orientation on Quadrupedal Gait Kinematics in Mouse Lemurs (Microcebus murinus)

“…Contrary to our predictions, however, mouse lemurs did not slow down on smaller or nonhorizontal substrates, suggesting that dynamic stability mitigated the need to reduce speed on more challenging substrates (Schmidt and Fischer, ; Chadwell and Young, ). The ability to maintain speed in the face of decreasing substrate diameter or nonhorizontal orientation is not restricted to primates, but is one of several speed‐related strategies (i.e., speed up, slow down, maintain speed) exhibited by small arboreal (and semiterrestrial) mammals when faced with the biomechanical challenge of variation in substrate diameter or orientation (Pridmore, ; Schmitt, ; Delciellos and Vieira, ; Stevens, ; Young, ; Schmidt and Fischer, , ; Hyams et al., ; Shapiro et al., ; Hesse et al., ; Karantanis et al., ).…”

“…Although there remains disagreement in the literature as to primate ancestral body size (Soligo and Martin, , ; Silcox et al., ), a presumed small body size for the primate ancestral condition (i.e., less than 100 g) (e.g., Cartmill, ; Gebo, ) is well supported by the small size of the earliest fossil euprimates (Silcox et al., ; Fleagle, ), and by the fact that agreement between paleontological and molecular estimates of primate divergence times improves when molecular models account for the fast life history patterns associated with a small bodied last common ancestor (Steiper and Seiffert, ). Accordingly, insights on primate locomotor evolution have been gained from studies examining the unique biomechanical benefits and challenges encountered by small primates or other small mammals moving quadrupedally on arboreal substrates (Pridmore, ; Preuschoft et al., ; Arms et al., ; Lemelin et al., ; Lammers and Biknevicius, ; Lammers et al., ; Lemelin and Schmitt, ; Lammers, , ; Lammers and Gauntner, ; Schmidt, ; Youlatos, ; Young, ; Samaras and Youlatos, ; Schmidt and Fischer, , ; Shapiro and Young, , ; Byron et al., ; Lammers and Zurcher, ; Stevens et al., ; Urbani and Youlatos, ; Shapiro et al., ; Chadwell and Young, ; Hesse et al., ; Karantanis et al., ). Most previous studies of primate quadrupedalism have been restricted to the analysis of symmetrical gaits.…”

“…ancestor (Steiper and Seiffert, 2012). Accordingly, insights on primate locomotor evolution have been gained from studies examining the unique biomechanical benefits and challenges encountered by small primates or other small mammals moving quadrupedally on arboreal substrates (Pridmore, '94;Preuschoft et al, '96;Arms et al, 2002;Lemelin et al, 2003;Lammers and Biknevicius, 2004;Lammers et al, 2006;Lemelin and Schmitt, 2007;Lammers, 2007Lammers, , 2009Lammers and Gauntner, 2008;Schmidt, 2008;Youlatos, 2008;Young, 2009;Samaras and Youlatos, 2010;Fischer, 2010, 2011;Young, 2010, 2012;Byron et al, 2011;Lammers and Zurcher, 2011;Stevens et al, 2011;Urbani and Youlatos, 2013;Shapiro et al, 2014;Chadwell and Young, 2015;Hesse et al, 2015;Karantanis et al, 2015). Most previous studies of primate quadrupedalism have been restricted to the analysis of symmetrical gaits.…”

A user's guide for the quantitative analysis of substrate characteristics and locomotor kinematics in free‐ranging primates

“…Several laboratories studies found that substrate orientation had significant effects on gait kinematics (Birn‐Jeffrey & Higham, ; Hesse, Nyakatura, Fischer, & Schmidt, ; Nyakatura, Fischer, & Schmidt, ; Prost & Sussman, ; Rollinson & Martin, ; Shapiro & Young, ; Shapiro et al, , ; Vilensky, Moore, & Libii, ). Field researchers examining qualitative locomotor categories, as well as gait kinematics, typically assign substrate orientations to a few categories (e.g., horizontal, oblique, and vertical) (Garber & Pruetz, ; Gebo & Chapman, ; Nyakatura & Heymann, ; Stevens et al, ; Youlatos, ).…”

Developments in development: What have we learned from primate locomotor ontogeny?

“…Alternatively, if the body's center of mass lies behind the line connecting the supporting diagonal limb pair (as it theoretically would be in a primate with a caudally positioned center of mass), the hindlimb of the diagonal swinging limb pair should land first, encompassing the center of gravity vector within the supporting three limbs, preventing backward pitch, and resulting in a DS gait. This explanation, known as the “Support Polygon Model” (Cartmill et al, ; Gray, ; Hildebrand, ; Tomita, ; Young, ), is problematic for the following reasons: 1) the position of the whole body center of mass of primates is not particularly caudal—in the few primate species in which whole body COM has been measured, it appears to be located relatively close to the craniocaudal midline (Crompton, Li, Alexander, Wang, & Günther, ; Druelle et al, ; Grand, ; Raichlen, Pontzer, Shapiro, & Sockol, ; Reynolds, ; Turnquist & Wells, ; Vilensky, ; Wells & DeMenthon, ; Young, ); 2) experimental manipulations of body COM in primates, or comparisons of primates with COM shifts due to tail fattening, do not result in predicted changes of footfall sequences (Young, Patel, & Stevens, ); 3) regardless of the position of the body's center of mass, primates readily switch from DS to LS gaits under certain conditions (e.g., when moving from a narrow pole to the flat ground: Hesse, Nyakatura, Fischer, & Schmidt, ; Prost & Sussman, ; Shapiro, Young, & Souther, ; Stevens, ; Vilensky & Larson, ; Vilensky & Patrick, ; Vilensky et al, ; Wallace & Demes, ) 4) in DS gaits, the landing hindlimb of a diagonal pair is not necessarily in a position to prevent backward pitch, and at that moment the direction of pitch is likely forward anyway (Cartmill et al, ); 5) the Support Polygon Model is based on static stability, and primates most likely rely more often on dynamic stability when travelling at any appreciable speed (Chadwell & Young, ; Lammers & Zurcher, ; Larson & Stern, ; Vilensky & Larson, ; Young et al, ; Young, Russo, Fellmann, Thatikunta, & Chadwell, ); and 6) the idea that primates have a more caudal COM has been conflated with the hindlimb “dominance” of primates compared to other mammals (i.e., higher substrate reaction forces on hind compared to forelimbs). Yet limb force distribution does not necessarily equate to center of mass position; greater weight support on primate hindlimbs may stem from the location of the body COM relative to the limbs, the kinematic positioning of the hands and feet relative to the COM (regardless of the latter's fore‐aft position), or an active shift to ...…”