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1. Great ape walking kinematics: Implications for hominoid evolution

   https://doi.org/10.1002/ajpa.23397  

   Finestone, Emma M. ; Brown, Mary H. ; Ross, Stephen R. ; Pontzer, Herman ( January 2018 , American Journal of Physical Anthropology)

   Great apes provide a point of reference for understanding the evolution of locomotion in hominoids and early hominins. We assessed (1) the extent to which great apes use diagonal sequence, diagonal couplet gaits, like other primates, (2) the extent to which gait and posture vary across great apes, and (3) the role of body mass and limb proportions on ape quadrupedal kinematics.

   High‐speed digital video of zoo‐housed bonobos (Pan paniscus, N = 8), chimpanzees (Pan troglodytes, N = 13), lowland gorillas (Gorilla gorilla, N = 13), and orangutans (Pongo spp. N = 6) walking over‐ground at self‐selected speeds were used to determine the timing of limb touch‐down, take‐off, and to measure joint and segment angles at touch‐down, midstance, and take‐off.

   The great apes in our study showed broad kinematic and spatiotemporal similarity in quadrupedal walking. Size‐adjusted walking speed was the strongest predictor of gait variables. Body mass had a negligible effect on variation in joint and segment angles, but stride frequency did trend higher among larger apes in analyses including size‐adjusted speed. In contrast to most other primates, great apes did not favor diagonal sequence footfall patterns, but exhibited variable gait patterns that frequently shifted between diagonal and lateral sequences.

   Similarities in the terrestrial walking kinematics of extant great apes likely reflect their similar post‐cranial anatomy and proportions. Our results suggest that the walking kinematics of orthograde, suspensory Miocene ape species were likely similar to living great apes, and highlight the utility of videographic and behavioral data in interpreting primate skeletal morphology.

    

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2. In vivo deciduous dental eruption in LuiKotale bonobos and Gombe chimpanzees

   https://doi.org/10.1002/ajpa.24376  

   Lee, Sean M. ; Sutherland, L. J. ; Fruth, Barbara ; Murray, Carson M. ; Lonsdorf, Elizabeth V. ; Arbenz‐Smith, Keely ; Augusto, Rafael ; Brogan, Sean ; Canington, Stephanie L. ; Lee, Kevin C. ; et al ( July 2021 , American Journal of Physical Anthropology)

   Existing data on bonobo and chimpanzee dental eruption timing are derived predominantly from captive individuals or deceased wild individuals. However, recent advances in noninvasive photographic monitoring of living, wild apes have enabled researchers to characterize dental eruption in relatively healthy individuals under naturalistic conditions. At present, such data are available for only one population of wild chimpanzees. We report data for an additional population of wild chimpanzees and the first dental eruption data for wild bonobos.

   We collected photographs and video footage of teeth from the open mouths of wild bonobos and East African chimpanzees of known age from LuiKotale, Democratic Republic of the Congo, and Gombe National Park, Tanzania, respectively. We scored the presence and absence of deciduous teeth from photographs and video footage to characterize deciduous dental eruption timing in these two populations.

   Deciduous dental eruption ages in our sample fall within the range of variation previously documented for captive chimpanzees, but eruption ages are later in wild than in captive contexts. We found substantial variation in deciduous canine eruption timing, particularly among bonobos. One bonobo had a deciduous canine present by 227 days old while another did not have a deciduous canine present at 477 days old.

   Our data indicate that deciduous teeth erupt later in wild individuals than in captive individuals. We also found that deciduous dental eruption timing varies considerably between individuals within our study populations, a pattern that is consistent with previous studies. Future studies should consider sources of variation in deciduous canine eruption timing and relationships with other aspects of life history as additional data become available.

    

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3. Orangutan Nesting Behavior in Gunung Palung National Park, West Kalimantan, Indonesia

   Brubaker-Wittman, L ; Blackburn, A ; DiGiorgio, A ; Harwell, FS ; Kane, EE: ; Knott, CD. ( March 2019 , American journal of physical anthropology)

   Nesting behavior is unique to the great apes among primates and has wide ranging implications for understanding socioecology and conservation. While much is known about nesting in gorillas, chimpanzees, and some orangutan populations living in disturbed forest and peat swamp, the nesting behavior of orangutans living in primary forest is poorly understood. We studied the nesting behavior of Bornean orangutans (Pongo pygmaeus wurmbii) in Gunung Palung National Park, West Kalimantan, Indonesia, using observations of 4,526 nesting events collected between October 1994 and September 2018, testing hypotheses about nest height. We found a significant effect of age/sex on nest height (F(3)=106.1, p<0.001). Post-hoc comparisons (adjusted α-level= 0.008) showed that flanged males nested significantly lower than all other age/sex classes (p<0.001) while females nested significantly lower than juveniles and unflanged males (p<0.001). Flanged males and females tended to nest lower in the canopy when alone than in the presence of other orangutans (males: F(3)=24.25, p<0.001; females: F(3)=5.83, p=0.001). Our results help demonstrate that across forest types, flanged male orangutans prefer to nest lower in the canopy while all other age- and sex-classes prefer higher canopy positions for nesting. Furthermore, our finding that solitary individuals nest lower than individuals near other orangutans suggests that nesting higher in the canopy may allow individuals to space their nests optimally when in proximity of other orangutans. These results have significant conservation implications, as logging and deforestation fundamentally change the forest structure, disrupting the canopy and making preferred nesting locations unavailable. 

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4. Unexpected terrestrial hand posture diversity in wild mountain gorillas

   https://doi.org/10.1002/ajpa.23404  

   Thompson, Nathan E. ; Ostrofsky, Kelly R. ; McFarlin, Shannon C. ; Robbins, Martha M. ; Stoinski, Tara S. ; Almécija, Sergio ( January 2018 , American Journal of Physical Anthropology)

   Gorillas, along with chimpanzees and bonobos, are ubiquitously described as ‘knuckle‐walkers.’ Consequently, knuckle‐walking (KW) has been featured pre‐eminently in hypotheses of the pre‐bipedal locomotor behavior of hominins and in the evolution of locomotor behavior in apes. However, anecdotal and behavioral accounts suggest that mountain gorillas may utilize a more complex repertoire of hand postures, which could alter current interpretations of African ape locomotion and its role in the emergence of human bipedalism. Here we documented hand postures during terrestrial locomotion in wild mountain gorillas to investigate the frequency with which KW and other hand postures are utilized in the wild.

   Multiple high‐speed cameras were used to record bouts of terrestrial locomotion of 77 habituated mountain gorillas at Bwindi Impenetrable National Park (Uganda) and Volcanoes National Park (Rwanda).

   We captured high‐speed video of hand contacts in 8% of the world's population of mountain gorillas. Our results reveal that nearly 40% of these gorillas used “non‐KW” hand postures, and these hand postures constituted 15% of all hand contacts. Some of these “non‐KW” hand postures have never been documented in gorillas, yet match hand postures previously identified in orangutans.

   These results highlight a previously unrecognized level of hand postural diversity in gorillas, and perhaps great apes generally. Although present at lower frequencies than KW, we suggest that the possession of multiple, versatile hand postures present in wild mountain gorillas may represent a shared feature of the African ape and human clade (or even great ape clade) rather than KWper se.

    

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5. Fecal Temperature of Wild and Captive Bornean Orangutans (Pongo pygmaeus wurmbii) as a Proxy for Body Temperature

   Syainullah, Muhammad ; Harwell, Faye S ; Gotama, Rinaldi ; Junardi, Junardi ; Scott, Katherine S ; Philp, Brodie ; Susanto, Tri Wahyu ; Knott, Cheryl D ( October 2019 , International Conference on Biodiversity for Life: Sustainable Development of Indonesian Biodiversity)

   Primate health status affects individual fitness and survival, yet is difficult to noninvasively investigate in the wild. Using a method tested on chimpanzees and humans, we estimated temperature of fecal samples of Bornean orangutans as a proxy for body temperature. Upon defecation, we recorded peak internal temperature of the samples. Estimated body temperature was influenced by height of defecation (r= -0.23, N= 95, P= 0.0004) and sample weight (r= 0.23, N= 75, P= 0.0475). These estimates were not affected by sex (F(2,92)= 0.431, P= 0.651) or weather (F(2,92)= 1.175, P= 0.313). Our method allowed for fast, consistent sampling, such that time from defecation to collection did not affect the results (r= -0.074, N= 95, P= 0.468), confirming reliable fecal temperatures can be collected from orangutans. We compare our results from the field to captive fecal samples, finding higher body temperatures in captivity. From our samples (N=95), orangutans appear to have a lower internal body temperature (33.44 ± 1.74 °C) on average than either chimpanzees or humans. Previous studies have demonstrated that orangutans have a lower metabolic rate than other great apes. Lower body temperature may serve as a metabolic adaptation of orangutans to survive extended periods of low food availability when energy must be conserved. 

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