Skeletal morphology of the lesula (Cercopithecus lomamiensis) and the evolution of guenon locomotor behavior.

OBJECTIVES: The guenons (tribe Cercopithecini) are a diverse and primarily arboreal radiation of Old World monkeys from Africa. However, preliminary behavioral observations of the lesula (Cercopithecus lomamiensis), a little-known guenon species described in 2012, report it spending substantial amounts of time on the ground. New specimens allow us to present the first description of lesula postcranial morphology and apply a comparative functional morphology approach to supplement our knowledge of its locomotor behavior. MATERIALS AND METHODS: To infer the substrate use preferences of the lesula, 22 postcranial variables correlated with locomotion were assessed in a sample of 151 adult guenon specimens, including two C. lomamiensis. Using multivariate statistical analyses, we predict the amount of time the lesula spends on the ground relative to the comparative sample. RESULTS: Results suggest that the lesula spends nearly half its time on the ground, and the two available individuals were classified as semiterrestrial and terrestrial with strong support. Comparisons with two outgroup cercopithecid taxa (Colobus guereza and Macaca mulatta) demonstrate that, as a group, guenons retain signals of a generalized, semiterrestrially adapted postcranium compared to specialized arboreal cercopithecids. DISCUSSION: These results corroborate preliminary behavioral observations of the lesula as a semiterrestrial to terrestrial primate and imply multiple evolutionary transitions in substrate use among the guenon radiation. A broader view of cercopithecoid evolution suggests that a semiterrestrial ancestor for extant guenons is more parsimonious than an arboreal one, indicating that the arboreal members of the group are probably recently derived from a more semiterrestrial ancestor.

Morphoarchitectural variation in South African fossil cercopithecoid endocasts.

Despite the abundance of well-preserved crania and natural endocasts in the South African Plio-Pleistocene cercopithecoid record, which provide direct information relevant to the evolution of their endocranial characteristics, few studies have attempted to characterize patterns of external brain morphology in this highly successful primate Superfamily. The availability of non-destructive penetrating radiation imaging systems, together with recently developed computer-based analytical tools, allow for high resolution virtual imaging and modeling of the endocranial casts and thus disclose new perspectives in comparative paleoneurology. Here, we use X-ray microtomographic-based 3D virtual imaging and quantitative analyses to investigate the endocranial organization of 14 cercopithecoid specimens from the South African sites of Makapansgat, Sterkfontein, Swartkrans, and Taung. We present the first detailed comparative description of the external neuroanatomies that characterize these Plio-Pleistocene primates. Along with reconstruction of endocranial volumes, we combine a semi-automatic technique for extracting the neocortical sulcal pattern together with a landmark-free surface deformation method to investigate topographic differences in morphostructural organization. Besides providing and comparing for the first time endocranial volume estimates of extinct Plio-Pleistocene South African cercopithecoid taxa, we report additional information regarding the variation in the sulcal pattern of Theropithecus oswaldi subspecies, and notably of the central sulcus, and the neuroanatomical condition of the colobine taxon Cercopithecoides williamsi, suggested to be similar for some aspects to the papionin pattern, and discuss potential phylogenetic and taxonomic implications. Further research in virtual paleoneurology, applied to specimens from a wider geographic area, is needed to clarify the polarity, intensity, and timing of cortical surface evolution in cercopithecoid lineages.

Degree of terrestrial activity of the elusive sun-tailed monkey (Cercopithecus solatus) in Gabon: Comparative study of behavior and postcranial morphometric data.

We carried out a multidisciplinary study linking behavioral and morphological data from a little-known guenon species, Cercopithecus solatus, endemic to Gabon. Over a period of 9 months, we documented the pattern of stratum use associated with postural and locomotor behavior by direct observation (650 hrs) of a semi-free-ranging breeding colony. We also conducted a morphometric analysis of the humerus and limb proportions of 90 adult specimens from 16 guenon species, including C. solatus. Field observations indicated that C. solatus monkeys spent a third of their time on the ground, similar to semi-terrestrial guenon species. We detected two patterns of stratum use: at ground level, and in trees, at a height of 3-10 m. The monkeys spent more time on the ground during the dry season than the wet season, feeding mainly at ground level, while resting, and social behaviors occurred more frequently in the tree strata. Our study of humerus size and shape, together with the analysis of limb proportions, indicated morphofunctional adaptation of C. solatus to greater terrestriality than previously thought. We therefore characterize C. solatus as a semi-terrestrial guenon, and propose a new hypothesis for the ancestral condition. By combining behavioral and morphological results, we provide new information about the adaptive strategies of the species, and the evolutionary history of guenons, thus contributing to the conservation of the sun-tailed monkey in the wild.

Lesula: a new species of Cercopithecus monkey endemic to the Democratic Republic of Congo and implications for conservation of Congo's central basin.

In June 2007, a previously undescribed monkey known locally as "lesula" was found in the forests of the middle Lomami Basin in central Democratic Republic of Congo (DRC). We describe this new species as Cercopithecus lomamiensis sp. nov., and provide data on its distribution, morphology, genetics, ecology and behavior. C. lomamiensis is restricted to the lowland rain forests of central DRC between the middle Lomami and the upper Tshuapa Rivers. Morphological and molecular data confirm that C. lomamiensis is distinct from its nearest congener, C. hamlyni, from which it is separated geographically by both the Congo (Lualaba) and the Lomami Rivers. C. lomamiensis, like C. hamlyni, is semi-terrestrial with a diet containing terrestrial herbaceous vegetation. The discovery of C. lomamiensis highlights the biogeographic significance and importance for conservation of central Congo's interfluvial TL2 region, defined from the upper Tshuapa River through the Lomami Basin to the Congo (Lualaba) River. The TL2 region has been found to contain a high diversity of anthropoid primates including three forms, in addition to C. lomamiensis, that are endemic to the area. We recommend the common name, lesula, for this new species, as it is the vernacular name used over most of its known range.

Functional morphology of cercopithecoid primate metacarpals.

The primate fossil record suggests that terrestriality was more common in the past than it is today, particularly among cercopithecoid primates. Whether or not a fossil primate habitually preferred terrestrial substrates has typically been inferred from its forelimb anatomy. Because extant large-bodied terrestrial cercopithecine monkeys utilize digitigrade hand postures during locomotion, being able to identify if a fossil primate habitually adopted digitigrade postures would be particularly revealing of terrestriality in this group. This paper examines the functional morphology of metacarpals in order to identify osteological correlates of digitigrade versus palmigrade hand postures. Linear measurements were obtained from 324 individuals belonging to digitigrade and palmigrade cercopithecoid species and comparisons were made between hand posture groups. Digitigrade taxa have shorter metacarpals, relative to both body mass and humerus length, than palmigrade taxa. Also, digitigrade taxa tend to have metacarpals with smaller dorsoventral diameters, relative to the product of body mass and metacarpal length, compared to palmigrade taxa. The size and shape of the metacarpal heads do not significantly differ between hand posture groups. Multivariate analyses suggest that metacarpal shape can only weakly discriminate between hand posture groups. In general, while there are some morphological differences in the metacarpals between hand posture groups, similarities also exist that are likely related to the fact that even digitigrade cercopithecoids can adopt palmigrade hand postures in different situations (e.g., terrestrial running, arboreal locomotion), and/or that the functional demands of different hand postures are not reflected in all aspects of metacarpal morphology. Therefore, the lack of identifiable adaptations for specific hand postures in extant cercopithecoids makes it difficult to determine a preference for specific habitats from fossil primate hand bones.

Brief communication: Contributions of enamel-dentine junction shape and enamel deposition to primate molar crown complexity.

Molar crown morphology varies among primates from relatively simple in some taxa to more complex in others, with such variability having both functional and taxonomic significance. In addition to the primary cusps, crown surface complexity derives from the presence of crests, cuspules, and crenulations. Developmentally, this complexity results from the deposition of an enamel cap over a basement membrane (the morphology of which is preserved as the enamel-dentine junction, or EDJ, in fully formed teeth). However, the relative contribution of the enamel cap and the EDJ to molar crown complexity is poorly characterized. In this study we examine the complexity of the EDJ and enamel surface of a broad sample of primate (including fossil hominin) lower molars through the application of micro-computed tomography and dental topographic analysis. Surface complexity of the EDJ and outer enamel surface (OES) is quantified by first mapping, and then summing, the total number of discrete surface orientation patches. We investigate the relative contribution of the EDJ and enamel cap to crown complexity by assessing the correlation in patch counts between the EDJ and OES within taxa and within individual teeth. We identify three patterns of EDJ/OES complexity which demonstrate that both crown patterning early in development and the subsequent deposition of the enamel cap contribute to overall crown complexity in primates.

Cheek pouch use, predation risk, and feeding competition in blue monkeys (Cercopithecus mitis stuhlmanni).

The adaptive function of cheek pouches in the primate subfamily Cercopithecinae remains unresolved. By analyzing the circumstances of cheek pouch use, we tested two hypotheses for the evolution of cercopithecine cheek pouches proposed in earlier studies: (1) cheek pouches reduce vulnerability to predation, and (2) cheek pouches increase feeding efficiency by reducing competition. We studied two groups of wild blue monkeys (Cercopithecus mitis stuhlmanni) in the Kakamega Forest, Kenya, conducting focal observations of feeding individuals. Monkeys were less exposed while emptying their cheek pouches than filling them, supporting the predation-avoidance hypothesis. We investigated several measures of competitive threat, but only one supported the competition-reduction hypothesis: when the nearest neighbor's rank increased, subjects were more likely to increase than to decrease cheek pouch use. Overall, our findings supported the predation-avoidance hypothesis more strongly than the competition-reduction hypothesis. We suggest that variation in cheek pouch use may reflect differing behavioral strategies used by cercopithecines to mitigate competition and predation, as well as factors such as resource size and distribution, home range size, and travel patterns.

Morphological structures and protrusive cranial border guidance of the temporomandibular joint of Cercopithecus mona.

Morphological parameters of the temporomandibular joint (TMJ) of Cercopithecus mona were analyzed by sagittal medial/lateral slicing of the entire joint. The slice contours of the osseous structures of the joint surfaces were approximated by circles. In this manner, the main parameter of the protrusive cranial border guidance, the protrusive dimeric Link chain (DLC), could be measured. In each joint, all slices yielded protrusive DLCs which were nearly parallel to each other. In medial/lateral direction all parts of the joints participate in force transmission in initial protrusive cranial border function.

Vocal production mechanisms in a non-human primate: morphological data and a model.

Human beings are thought to be unique amongst the primates in their capacity to produce rapid changes in the shape of their vocal tracts during speech production. Acoustically, vocal tracts act as resonance chambers, whose geometry determines the position and bandwidth of the formants. Formants provide the acoustic basis for vowels, which enable speakers to refer to external events and to produce other kinds of meaningful communication. Formant-based referential communication is also present in non-human primates, most prominently in Diana monkey alarm calls. Previous work has suggested that the acoustic structure of these calls is the product of a non-uniform vocal tract capable of some degree of articulation. In this study we test this hypothesis by providing morphological measurements of the vocal tract of three adult Diana monkeys, using both radiography and dissection. We use these data to generate a vocal tract computational model capable of simulating the formant structures produced by wild individuals. The model performed best when it combined a non-uniform vocal tract consisting of three different tubes with a number of articulatory manoeuvres. We discuss the implications of these findings for evolutionary theories of human and non-human vocal production.

Comparative postcranial body shape and locomotion in Chlorocebus aethiops and Cercopithecus mitis.

Body weight and length, chest girth, and seven postcranial limb segment lengths are compared between two guenon species, Chlorocebus (Cercopithecus) aethiops (vervets) and Cercopithecus mitis (blue monkeys), exhibiting different habitual locomotor preferences. The subjects, all adults, were wild caught for a non-related research project (Turner et al. [1986] Genetic and morphological studies on two species of Kenyan monkeys, C. aethiops and C. mitis. In: Else JG, Lee PC, editors. Primate evolution, proceedings of the Xth International Congress of Primatology, Cambridge. London). The morphological results are interpreted within the context of previously published observations of primate locomotion and social organization. The sample is unique in that the body weight of each individual is known, allowing the effects of body-size scaling to be assessed in interspecific and intersexual comparisons. C. mitis has a significantly (P < 0.05) greater body weight and trunk length than C. aethiops. A shorter trunk may function to reduce spinal flexibility for ground-running in the latter. Proximal limb segments (arm and thigh) are significantly greater in C. mitis, reflecting known adaptations to committed arboreal quadrupedal locomotion. By contrast, relative distal limb segments (forearm, crus, and foot) are significantly longer in C. aethiops, concordant with a locomotor repertoire that includes substantial terrestrial quadrupedalism, in addition to arboreal agility, and also the requisite transition between ground and canopy. Although normally associated with arboreal monkeys, greater relative tail length occurs in the more terrestrial vervets. However, because vervets exploit both arboreal and terrestrial habitats, a longer tail may compensate for diminished balance during arboreal quadrupedalism resulting from the greater "brachial" and "crural" indices that enhance their ground quadrupedalism. Most interspecific differences in body proportions are explicable by differences in locomotor modalities. Some results, however, contradict commonly held "tenets" that relate body size and morphology exclusively to locomotion. Generally associated with terrestriality, sexual dimorphism (male/female) is greater in the more arboreal blue monkeys. A more intense, seasonal mating competition may account for this incongruity.

Partial cranium of Cercopithecoides kimeui Leakey, 1982 from Rawi Gully, southwestern Kenya.

The Rawi Gully, located on the Homa Peninsula in southwestern Kenya, has produced several fossil elements of a large cercopithecid from sediments approximately 2.5 million years old (Ma). Nearly all of these elements appear to represent a single adult male individual of the colobine species Cercopithecoides kimeui Leakey, 1982. Part of the face, mandible, dentition, and several small postcranial fragments were collected by the Homa Peninsula Paleoanthropological Project (HPPP) in 1994 and 1995. This individual also appears to be represented by material collected in two previous expeditions to the site, one led by David Pilbeam in the 1970s and an earlier expedition led by L.S.B. Leakey in 1933. This specimen may extend the first appearance of C. kimeui by approximately 500 Kyr, and provides the first evidence for much of the male facial morphology in this species. Furthermore, Rawi may represent a more wooded habitat than the other occurrences of C. kimeui at Olduvai Gorge, Tanzania, and Koobi Fora, Kenya, indicating that C. kimeui may have been relatively flexible in its habitat preferences.

Fiber architecture of the intrinsic muscles of the shoulder and arm in semiterrestrial and arboreal guenons.

The internal organization of myofibers and connective tissues has important physiologic implications for muscle function and for naturalistic behavior. In this study of forelimb muscle morphology and primate locomotion, fiber architecture is examined in the intrinsic muscles of the shoulder (musculi deltoideus, infraspinatus, supraspinatus, subscapularis, teres major, and t. minor) and arm (m. coracobrachialis, biceps brachii, brachialis, and triceps brachii) in the semiterrestrial vervets (Chlorocebus aethiops) and arboreal red-tailed guenons (Cercopithecus ascanius). Wet weights and lengths of whole muscles, lengths of fasciculi and their associated proximal and distal tendons, and angles of pinnation were measured to estimate morphologic correlates of physiologic properties of individual muscles: force, velocity/excursion, energy expense, and relative isometric or isotonic contraction. Neither mean total-shoulder:total-arm ratios for muscle mass nor total reduced physiological cross-sectional area exhibited significant (P < 0.05) interspecific differences, thus emphasizing the importance of fine-tuning musculoskeletal analyses by the data collected here. The results generally support those previously published for quadriceps femoris and triceps surae of the hind limb in these species (Anapol and Barry [1996] Am. J. Phys. Anthropol. 99:429-447). The fiber architecture of the semiterrestrial vervets is largely suited for higher velocity while running on the ground. By contrast, the architectural configuration of red-tailed monkeys implies relatively isometric muscle contraction and passive storage of elastic strain energy for exploitation of the compliant canopy, where substrate components are situated beneath the sagittal plane of the animal. With respect to relative distribution of maximum potential force output among muscles of either shoulder or arm groups in these otherwise hind limb-dominated quadrupedal primates, statistically significant interspecific differences are best interpreted in light of braking, climbing, and, for vervets, the transition between ground and canopy. The interspecific differences shown here for the intrinsic muscles of the shoulder and arm underscore the significance of intramuscular morphology in reconciling structure and function with regard to locomotor behavior. Its analysis and interpretation lend support to consideration of "semiterrestrial" as a bona fide locomotor category uniquely different from what is practiced by dedicated arboreal and terrestrial quadrupeds that occasionally visit the habitat of one another. Data from a more committed terrestrial species would clarify this enigma.

Functional neuroanatomy of the primate isocortical motor system.

The concept of the primate motor cortex based on the cytoarchitectonic subdivision into areas 4 and 6 according to Brodmann or the functional subdivision into primary motor, supplementary motor, and lateral premotor cortex has changed in recent years. Instead, this cortical region is now regarded as a complex mosaic of different areas. This review article gives an overview of the structure and function of the isocortical part of the motor cortex in the macaque and human brain. In the macaque monkey, the primary motor cortex (Brodmann's area 4 or area F1) with its giant pyramidal or Betz cells lies immediately anterior to the central sulcus. The non-primary motor cortex (Brodmann's area 6) lies further rostrally and can be subdivided into three groups of areas: the supplementary motor areas "SMA proper" (area F3) and "pre-SMA" (area F6) on the mesial cortical surface, the dorsolateral premotor cortex (areas F2 and F7) on the dorsolateral convexity, and the ventrolateral premotor cortex (areas F4 and F5) on the ventrolateral convexity. The primary motor cortex is mainly involved in controlling kinematic and dynamic parameters of voluntary movements, whereas non-primary motor areas are more related to preparing voluntary movements in response to a variety of internal or external cues. Since a structural map of the human isocortical motor system as detailed as in the macaque is not yet available, homologies between the two species have not been firmly established. There is increasing evidence, however, that a similar organizational principle (i.e., primary motor cortex, supplementary motor areas, dorso- and ventrolateral premotor cortex) also exists in humans. Imaging studies have revealed that functional gradients can be discerned within the human non-primary motor cortex. More rostral cortical regions are active when a motor task is nonroutine, whereas more routine motor actions engage more caudal areas.

Retinal projections to the pregeniculate nucleus in the hemispherectomized monkey.

Intraocular injections of tritiated proline were used to test the hypothesis that unilateral removal of all visual cortical areas results in increased distribution of retinal terminals in the pregeniculate nucleus (PGN) of the thalamus in monkeys. Following hemispherectomy, retinal input to the ipsilateral PGN was reduced by an average of 18.5% when compared to its contralateral homologue, which corresponded to the reduction in nuclear volume (19.3%). Our results show that removal of cortical afferents to the external layer of the PGN does not induce invasion of retinal projections into this region of the nucleus.

Capture techniques and morphological measurements of the mona monkey (Cercopithecus mona) on the island of Grenada, West Indies.

Morphological measurements were collected from 12 wild and 12 captive mona monkeys (Cercopithecus mona) on the Caribbean island of Grenada. Mona monkeys were introduced to Grenada from Africa approximately 200 to 300 years ago during the slave trade era. Wild monkeys were captured using either 1) a baited treadle-door trap and anesthetic-filled darts fired from a blowpipe, or 2) rifle-fired anesthetic-filled darts. All wild monkeys were released back into the forest after capture and were seen with their original groups within 24 hours of release. Captive monkeys were anesthetized using blowpipe-fired darts. A Ketaset/Rompun mixture was the most effective anesthetic for wild monkeys while Ketaset alone was suitable for captive monkeys. Responses to and recovery times from both drugs varied among individuals. Data on eight linear body measurements, canine length, testicle size, and weight were collected from all monkeys. Adult monkeys were significantly sexually dimorphic across all measurements. Mean adult male weight (mean = 4.7, SD = 0.9, n = 13) was almost twice that of adult females (mean = 2.8, SD = 0.8, n = 7). No significant differences in weight or measurements were found between adult wild and captive males. Preliminary comparisons with morphometrics for African C. mona from the literature showed the upper limit of Grenada mona body length and weight to be smaller than that of African monas for both sexes. These differences may be due to genetic divergence, ecological adaptation, inter-African geographic variation, and/or small sample sizes.

Fiber architecture of the extensors of the hindlimb in semiterrestrial and arboreal guenons.

Fiber architecture of the extensor musculature of the knee and ankle is examined in two African gueon species--the semiterrestrial Cercopithecus aethiops, and the arboreal C. ascanius. Using histologic and microscopic techniques to measure lengths of sarcomeres, the original lengths of muscle fasciculi and angles of pinnation in quadriceps femoris and triceps surae are reconstructed from direct measurements on cadavers. Calculations of reduced physiological cross-sectional area, mass/predicted effective tetanic tension, maximum excursion, and tendon length/fasciculus+tendon lengths are correlated to preferred locomotor modalities in the wild. For both species, greater morphological differences occur among the bellies of quadriceps femoris--rectus femoris, vastus intermedius, v. lateralis, and v. medialis--than among the bellies of triceps surae--gastrocnemius lateralis, g. medialis, plantaris, and soleus. With regard to quadriceps femoris, few differences occur between species. Interspecific differences in the triceps surae indicate (1) redirection of muscle force to accommodate arboreality in which the substrate is less than body width; (2) muscles more suited for velocity in the semiterrestrial vervets; and (3) muscles used more isotonically in vervets and more isometrically in red-tailed monkeys. The inherent flexibility of muscles may be preadaptive to a primary species shift in locomotor modality until the bony morphology is able to adapt through natural selection.

Positional behavior in five sympatric Old World monkeys.

Observations of positional behavior and habitat use were recorded on focal individuals of five species of Old World monkeys at Kibale Forest, Uganda, through the dry season of 1990 and 1991. Cercopithecus ascanius, Cercopithecus mitis, Cercocebus albigena, Colobus badius, and Colobus guereza commonly utilize five similar types of positional behavior (i.e., quadrupedalism, leaping, climbing, sitting, and standing), but in varying frequencies and situations. As a group, colobines use oblique supports and leap more often, and cover greater linear distances during leaps than do cercopithecines. Colobines also prefer to sit (about 90% of all postures), while cercopithecines stand more frequently. Body size differences between the sexes of a species are not reflected in positional behavior. The two small-bodied species climb more and leap less often than the three larger species, which is the reverse of what we would expect. Leaping is the most common method of crossing open spaces within the canopy; but most spatial gaps and leaps are over short distances, usually one meter or less. All five species, regardless of body size or the availability of forest supports, prefer medium-sized supports. Incorporating our work from Uganda with previous investigations of positional behavior reveals few consistent trends with respect to body size or habitat use across primates.

Phylogenetic, paleodemographic, and taphonomic implications of Victoriapithecus deciduous teeth from Maboko, Kenya.

More than 240 milk teeth of Victoriapithecus macinnesi, representing all elements of the deciduous dentition, are described. Their morphology is intermediate between that of hominoids and cercopithecids. Unlike colobine and cercopithecine milk teeth, Victoriapithecus dp3s, dp4s, and at least 7 (14%) dp4s lack transverse distal loph(id)s and are not bilophodont. Victoriapithecus also differs from cercopithecids in having less elongated deciduous premolars, a dp3 metacone set mesial to a very small hypocone, a dp4 crista obliqua, and a dp4 hypoconulid. The deciduous canines and incisors of Victoriapithecus are like those of other cercopithecids in having an uneven distribution of enamel around a compressed (rather than cylindrical) root, but differ from cercopithecids and resemble hominoids in being more elongated. Since Colobinae and Cercopithecinae share features of the deciduous dentition that are derived relative to Victoriapithecus and hominoids, extant Old World monkeys are interpreted as representing the sister-taxon of the middle Miocene cercopithecoids. Due to a dramatic increase in the number of deciduous teeth found at Maboko Island, juvenile individuals represent a much larger proportion of recently excavated Victoriapithecus collections than is true of pre-1987 assemblages which mainly derive from sediment first excavated during the 1930s and 1940s. Age distribution differences between pre- and post-1987 samples indicate that paleontological collection procedures were more important than taphonomic biases in determining the paleodemographic profile of the Maboko fossils. Since the Victoriapithecus assemblage from Maboko is strikingly similar to that of fossil Theropithecus oswaldi from Olorgesailie in terms of the large number of specimens and high representation of juvenile and infant individuals, the latter can no longer be viewed as unique among cercopithecoid fossil assemblages. Rather than being related to a specific cause of death, such as selective hunting of T. oswaldi by Homo (Shipman et al. [1981] Curr. Anthropol. 22:257-268), the large number of cercopithecoids at both sites is attributed to the fact that both assemblages represent excavated samples and that the preferred habitats of the extinct monkeys were probably at or near the site of deposition. The greater number of young adult male than female canines in the apparently attritional Maboko Bed 5 assemblage, indicate that the social organization of V. macinnesi may have been similar to that of modern macaques, with males migrating out of their natal group and suffering higher death rates than females at puberty.

Terrestrial adaptations in the postcranial skeletons of guenons.

Arboreal and semiterrestrial guenons show similar osteological features of the limbs across a wide range of species, environments, and geography, while the more terrestrially committed guenons exhibit greater morphological divergence. An ecomorphological comparison of two sympatric guenons living in Kibale Forest, Uganda, reveals an array of anatomical adaptations for terrestriality in the limbs of Cercopithecus lhoesti similar to those found in Erythrocebus patas. In contrast, Cercopithecus aethiops, although also frequent users of the terrestrial environment, generally exhibit fewer morphological adaptations characteristic of a terrestrial lifestyle. It appears that significant morphological modification for terrestriality has occurred twice within the diverse radiation of living guenons with C. aethiops perhaps representing a third group in the making.