Subchondral Bone Apparent Density and Locomotor Behavior in Extant Primates and Subfossil Lemurs Hadropithecus and Pachylemur

Locomotion of an adult female and juvenile male aye-aye (Daubentonia madagascariensis) in Torotorofotsy, Madagascar

Aye-ayes (Daubentonia madagascariensis) locate and acquire invertebrates from within woody substrates at all levels of the rainforest; yet how their locomotion helps them accommodate this diet has not been explored in detail. We studied the locomotor behavior of an adult female (N = 1,085) and juvenile male (N = 708) aye-aye in the undisturbed forest of Torotorofotsy, Madagascar from May to December 2017. We used bout sampling to record locomotion during foraging and travel of the two radio-collared individuals. We used χ ² tests to compare overall locomotion, travel, and foraging, as well as strata and support use. We performed a correspondence analysis to examine relationships between individual behaviors, strata, and support types. Leaping accounted for 47.9% and 50.1% of all locomotor activity in the adult female and juvenile male, respectively. Leaping was the most common behavior during travel in both individuals (59.2% and 53.9%, respectively), whereas head-first descent was most frequent during foraging (35.0% and 48.0%, respectively). For all three locomotor categories, the main canopy (40.3%-79.6%) was used most frequently and trunks were the most frequently used support type (50.7%-60.0%). There is a strong association between strata and support use overall and during travel. Quadrupedal walking was significantly associated with the main canopy, as was head-first descent with the low canopy. Our analysis demonstrates that aye-ayes use a variety of locomotor behaviors to forage for invertebrates. Aye-ayes' ability to repurpose their positional repertoire to acquire other resources in degraded forests should not obscure the importance of invertebrates to this species.

Subchondral Bone Radiodensity Patterns in the Glenoid Fossa of Ape and Human Scapulae

Regions of denser subchondral bone deep to a joint's articular surface indicate locations where the joint experiences relatively higher or more frequent compressive trans-articular forces than less dense regions. Human clinically focused studies have hypothesized that regional variation of acquired with computed tomography osteoabsorptiomety (CT-OAM), in the scapular glenoid fossa (GF) is specifically related to forces arising from everyday rotator cuff muscle function. We test this hypothesis by investigating the relationship between rotator cuff function and GF HiRD subchondral bone patterns in a broader comparative context. CT-OAM was used on scapulae of chimpanzees, gibbons and humans to visualize HiRD subchondral bone patterns and assess regional (anterior-posterior; superior-inferior) differences in HiRD concentrations within each group. Like patterns observed in humans, ape GFs show HiRD concentrations in anterior, posterior and superior regions. Gibbons exhibit significantly larger concentrations anteriorly, probably serving as a skeletal correlate of increased subscapularis activity during humeral internal rotation during arm-swinging locomotion. Chimpanzees exhibit relatively larger areas posteriorly (though not statistically significant), conceivably serving as a correlate of increased infraspinatus activity during humeral external rotation and retraction during knuckle-walking. All groups show relatively larger HiRD areas superiorly, likely correlating with forceful humeral abduction (rather than adduction) during routine upper limb use across behaviors. Subchondral bone HiRD patterns in the GF appear to correspond with normal and unbalanced rotator cuff activity and force production not only in humans, but also in other primates, thereby corroborating their value in human clinical studies and functional morphology research. Anat Rec, 301:776-785, 2018. © 2017 Wiley Periodicals, Inc.

Trabecular and cortical bone structure of the talus and distal tibia in Pan and Homo

OBJECTIVES

Internal bone structure, both cortical and trabecular bone, remodels in response to loading and may provide important information regarding behavior. The foot is well suited to analysis of internal bone structure because it experiences the initial substrate reaction forces, due to its proximity to the substrate. Moreover, as humans and apes differ in loading of the foot, this region is relevant to questions concerning arboreal locomotion and bipedality in the hominoid fossil record.

MATERIALS AND METHODS

We apply a whole-bone/epiphysis approach to analyze trabecular and cortical bone in the distal tibia and talus of Pan troglodytes and Homo sapiens. We quantify bone volume fraction (BV/TV), degree of anisotropy (DA), trabecular thickness (Tb.Th), bone surface to volume ratio (BS/BV), and cortical thickness and investigate the distribution of BV/TV and cortical thickness throughout the bone/epiphysis.

RESULTS

We find that Pan has a greater BV/TV, a lower BS/BV and thicker cortices than Homo in both the talus and distal tibia. The trabecular structure of the talus is more divergent than the tibia, having thicker, less uniformly aligned trabeculae in Pan compared to Homo. Differences in dorsiflexion at the talocrural joint and in degree of mobility at the talonavicular joint are reflected in the distribution of cortical and trabecular bone.

DISCUSSION

Overall, quantified trabecular parameters represent overall differences in bone strength between the two species, however, DA may be directly related to joint loading. Cortical and trabecular bone distributions correlate with habitual joint positions adopted by each species, and thus have potential for interpreting joint position in fossil hominoids.

Trabecular mapping: Leveraging geometric morphometrics for analyses of trabecular structure

OBJECTIVES

Trabecular microstructure of limb bone epiphyses has been used to elucidate the relationship between skeletal form and behavior among mammals. Such studies have often relied on the analysis of a single volume of interest (VOI). Here we present a method for evaluating variation in bone microstructure across articular surfaces by leveraging sliding semilandmarks.

METHODS

Two samples were used to demonstrate the proposed methodology and test the hypothesis that microstructural variables are homogeneously distributed: tali from two ape genera (Pan and Pongo, n = 9) and modern human distal femora (n = 10). Sliding semilandmarks were distributed across articular surfaces and used to locate the position of multiple VOIs immediately deep to the cortical shell. Trabecular bone properties were quantified using the BoneJ plugin for ImageJ. Nonparametric MANOVA tests were used to make group comparisons and differences were explored using principal components analysis and visualized using color maps.

RESULTS

Tests reveal that trabecular parameters are not distributed homogeneously and identify differences between chimpanzee and orangutan tali with regards to trabecular spacing and degree of anisotropy, with chimpanzee tali being more anisotropic and having more uniformly spaced trabeculae. Human males and females differed in the pattern of trabecular spacing with males having more uniform trabecular spacing across the joint surface.

CONCLUSIONS

The proposed procedure quantifies variation in trabecular bone parameters across joint surfaces and allows for meaningful statistical comparisons between groups of interest. Consequently it holds promise to help elucidate links between trabecular bone structure and animal behavior.

What did Hadropithecus eat, and why should paleoanthropologists care?

Over 40 years ago, Clifford Jolly noted different ways in which Hadropithecus stenognathus converged in its craniodental anatomy with basal hominins and with geladas. The Malagasy subfossil lemur Hadropithecus departs from its sister taxon, Archaeolemur, in that it displays comparatively large molars, reduced incisors and canines, a shortened rostrum, and thickened mandibular corpus. Its molars, however, look nothing like those of basal hominins; rather, they much more closely resemble molars of grazers such as Theropithecus. A number of tools have been used to interpret these traits, including dental microwear and texture analysis, molar internal and external morphology, and finite element analysis of crania. These tools, however, have failed to provide support for a simple dietary interpretation; whereas there is some consistency in the inferences they support, dietary inferences (e.g., that it was graminivorous, or that it specialized on hard objects) have been downright contradictory. Cranial shape may correlate poorly with diet. But a fundamental question remains unresolved: why do the various cranial and dental convergences exemplified by Hadropithecus, basal hominins, and Theropithecus exist? In this paper we review prior hypotheses regarding the diet of Hadropithecus. We then use stable carbon and nitrogen isotope data to elucidate this species' diet, summarizing earlier stable isotope analyses and presenting new data for lemurs from the central highlands of Madagascar, where Hadropithecus exhibits an isotopic signature strikingly different from that seen in other parts of the island. We offer a dietary explanation for these differences. Hadropithecus likely specialized neither on grasses nor hard objects; its staples were probably the succulent leaves of CAM plants. Nevertheless, aspects of prior hypotheses regarding the ecological significance of its morphology can be supported. Am. J. Primatol. 78:1098-1112, 2016. © 2015 Wiley Periodicals, Inc.

Trabecular architecture of the manual elements reflects locomotor patterns in primates

The morphology of trabecular bone has proven sensitive to loading patterns in the long bones and metacarpal heads of primates. It is expected that we should also see differences in the manual digits of primates that practice different methods of locomotion. Primate proximal and middle phalanges are load-bearing elements that are held in different postures and experience different mechanical strains during suspension, quadrupedalism, and knuckle walking. Micro CT scans of the middle phalanx, proximal phalanx and the metacarpal head of the third ray were used to examine the pattern of trabecular orientation in Pan, Gorilla, Pongo, Hylobates and Macaca. Several zones, i.e., the proximal ends of both phalanges and the metacarpal heads, were capable of distinguishing between knuckle-walking, quadrupedal, and suspensory primates. Orientation and shape seem to be the primary distinguishing factors but differences in bone volume, isotropy index, and degree of anisotropy were seen across included taxa. Suspensory primates show primarily proximodistal alignment in all zones, and quadrupeds more palmar-dorsal orientation in several zones. Knuckle walkers are characterized by having proximodistal alignment in the proximal ends of the phalanges and a palmar-dorsal alignment in the distal ends and metacarpal heads. These structural differences may be used to infer locmotor propensities of extinct primate taxa.