Metrical analysis of the basicranium of extant hominoids and Australopithecus

The size and shape of the basicranium (seen in norma basilaris) in Homo, Gorilla, Pan, Pongo, and Australopithecus have been studied by recording the relative disposition of midline and bilateral bony landmarks. Fifteen linear measurements and two angles were used to relate the landmarks. The relatively longer and narrower cranial base of Gorilla, Pan, and Pongo is clearly contrasted with the wider, shorter cranial base in Homo sapiens. When the same observations were made on two “robust” and two “gracile” australopithecine crania, marked differences were found between the taxa. In the two “robust” specimens, the foramen magnum is located relatively further forward, and the axis of the petrous temporal bone is aligned more nearly with the coronal plane than in the two “gracile” crania. The implications of this apparent parallelism in basicranial morphology between Homo sapiens and the “robust” australopithecines are discussed.     

Comparative locomotor behavior of chimpanzees and bonobos: The influence of morphology on locomotion

Results from a 10 month study of adult male and female bonobos (Pan paniscus) in the Lomako Forest, Zaire, and those from a 7 month study of adult male and female chimpanzees in the Tai Forest, Ivory Coast (Pan troglodytes verus), were compared in order to determine whether there are species differences in locomotor behavior and substrate use and, if so, whether these differences support predictions made on the basis of interspecific morphological differences. Results indicate that bonobos are more arboreal than chimpanzees and that male bonobos are more suspensory than their chimpanzee counterpart. This would be predicted on the basis of male bonobo's longer and more narrow scapula. This particular finding is contrary to the prediction that the bonobo is a “scaled reduced version of a chimpanzee” with little or no positional behavior difference as had been suggested. This study provides the behavioral data necessary to untangle contradictory interpretations of the morphological differences between chimpanzees and bonobos, and raises a previously discussed (Fleagle: Size and Scaling in Primate Biology, pp. 1–19, 1985) but frequently overlooked point–that isometry in allometric studies does not necessarily equate with behavioral equivalence. Several researchers have demonstrated that bonobos and chimpanzees follow the same scaling trends for many features, and are in some sense functionally equivalent, since they manage to feed and reproduce. However, as reflected in their morphologies, they do so through different types and frequencies of locomotor behaviors. © 1993 Wiley-Liss, Inc.     

Ontogeny of the hominoid scapula: The influence of locomotion on morphology

Primate shoulder morphology has been linked with locomotor habits, oftentimes irrespective of phylogenetic heritage. Among hominoids, juvenile African apes are known to climb more frequently than adults, while orangutans and gibbons maintain an arboreal lifestyle throughout ontogeny. This study examined if these ontogenetic locomotor differences carry a morphological signal, which should be evident in the scapulae of chimpanzees and gorillas but absent in taxa that do not display ontogenetic behavioral shifts. The scapular morphology of five hominoid primates and one catarrhine outgroup was examined throughout ontogeny to evaluate if scapular traits linked with arboreal activities are modified in response to ontogenetic behavioral shifts away from climbing. Specifically, the following questions were addressed: 1) which scapular characteristics distinguish taxa with different locomotor habits; and 2) do these traits show associated changes during development in taxa known to modify their behavioral patterns? Several traits characterized suspensory taxa from nonsuspensory forms, such as cranially oriented glenohumeral joints, obliquely oriented scapular spines, relatively narrow infraspinous fossae, and inferolaterally expanded subscapularis fossae. The relative shape of the dorsal scapular fossae changed in Pan, Gorilla, and also Macaca in line with predictions based on reported ontogenetic changes in locomotor behavior. These morphological changes were mostly distinct from those seen in Pongo, Hylobates, and Homo and imply a unique developmental pattern, possibly related to ontogenetic locomotor shifts. Accordingly, features that sorted taxa by locomotor habits and changed in concert with ontogenetic behavioral patterns should be particularly useful for reconstructing the locomotor habits of fossil forms. Am J Phys Anthropol 152:239–260, 2013. © 2013 Wiley Periodicals, Inc.     

Distal Humeral Morphology Indicates Locomotory Divergence in Extinct Giant Kangaroos

Previous studies of the morphology of the humerus in kangaroos showed that the shape of the proximal humerus could distinguish between arboreal and terrestrial taxa among living mammals, and that the extinct “giant” kangaroos (members of the extinct subfamily Sthenurinae and the extinct macropodine genus Protemnodon) had divergent humeral anatomies from extant kangaroos. Here, we use 2D geometric morphometrics to capture the shape of the distal humerus in a range of extant and extinct marsupials and obtain similar results: sthenurines have humeral morphologies more similar to arboreal mammals, while large Protemnodon species (P. brehus and P. anak) have humeral morphologies more similar to terrestrial quadrupedal mammals. Our results provide further evidence for prior hypotheses: that sthenurines did not employ a locomotor mode that involved loading the forelimbs (likely employing bipedal striding as an alternative to quadrupedal or pentapedal locomotion at slow gaits), and that large Protemnodon species were more reliant on quadrupedal locomotion than their extant relatives. This greater diversity of locomotor modes among large Pleistocene kangaroos echoes studies that show a greater diversity in other aspects of ecology, such as diet and habitat occupancy.

     

Angular momentum and arboreal stability in common marmosets (Callithrix jacchus)

Despite the importance that concepts of arboreal stability have in theories of primate locomotor evolution, we currently lack measures of balance performance during primate locomotion. We provide the first quantitative data on locomotor stability in an arboreal primate, the common marmoset (Callithrix jacchus), predicting that primates should maximize arboreal stability by minimizing side-to-side angular momentum about the support (i.e., L_sup). If net L_sup becomes excessive, the animal will be unable to arrest its angular movement and will fall. Using a novel, highly integrative experimental procedure we directly measured whole-body L_sup in two adult marmosets moving along narrow (2.5 cm diameter) and broad (5 cm diameter) poles. Marmosets showed a strong preference for asymmetrical gaits (e.g., gallops and bounds) over symmetrical gaits (e.g., walks and runs), with asymmetrical gaits representing >90% of all strides. Movement on the narrow support was associated with an increase in more “grounded” gaits (i.e., lacking an aerial phase) and a more even distribution of torque production between the fore- and hind limbs. These adjustments in gait dynamics significantly reduced net L_sup on the narrow support relative to the broad support. Despite their lack of a well-developed grasping apparatus, marmosets proved adept at producing muscular “grasping” torques about the support, particularly with the hind limbs. We contend that asymmetrical gaits permit small-bodied arboreal mammals, including primates, to expand “effective grasp” by gripping the substrate between left and right limbs of a girdle. This model of arboreal stability may hold important implications for understanding primate locomotor evolution. Am J Phys Anthropol 156:565–576, 2015. © 2014 Wiley Periodicals, Inc.     

Nestling tree swallows (Tachycineta bicolor) alter begging behaviour in response to odour of familiar adults,but not their nests

Communication using chemical cues is important for many taxa, including birds, but the use of olfaction for intraspecific communication has been investigated only recently in passerines and is understudied in nestlings. To address this knowledge gap, we explored whether nestling tree swallows (Tachycineta bicolor) would recognize and respond to chemical cues of conspecifics, specifically testing begging responses to familiar and unfamiliar nest and adult odours. For the nest odour experiment, nests were treated with either orange essential oil or distilled water to create scented and unscented (control) odour environments, respectively. For the adult odour experiment, adults attending the nestlings were considered “familiar adults” and adults attending a different brood in the population were considered “unfamiliar adults.” We found that begging responses of nestlings did not differ in response to orange oil odour or water, but nestlings begged significantly longer and more intensely in response to odours of a familiar than an unfamiliar adult, regardless of adult sex. This provides evidence that tree swallows use chemical cues to alter their behaviour and opens up many exciting avenues of future research.     

Sexual Dimorphism and Facial Growth Beyond Dental Maturity in Great Apes and Gibbons

The great apes and gibbons are characterized by extensive variation in degree of body size and cranial dimorphism, but although some studies have investigated how sexual dimorphism in body mass is attained in these species, for the majority of taxa concerned, no corresponding work has explored the full extent of how sexual dimorphism is attained in the facial skeleton. In addition, most studies of sexual dimorphism combine dentally mature individuals into a single “adult” category, thereby assuming that no substantial changes in size or dimorphism take place after dental maturity. We investigated degree and pattern of male and female facial growth in Pan troglodytes troglodytes, Pan paniscus, Gorilla gorilla gorilla, Pongo pygmaeus, and Hylobates lar after dental maturity through cross-sectional analyses of linear measurements and geometric mean values of the facial skeleton and age-ranking of individuals based on molar occlusal wear. Results show that overall facial size continues to increase after dental maturity is reached in males and females of Gorilla gorilla gorilla and Pongo pygmaeus, as well as in the females of Hylobates lar. In male Pongo pygmaeus, adult growth patterns imply the presence of a secondary growth spurt in craniofacial dimensions. There is suggestive evidence of growth beyond dental maturity in the females of Pan troglodytes troglodytes and Pan paniscus, but not in the males of those species. The results show the presence of statistically significant facial size dimorphism in young adults of Pan paniscus and Hylobates lar, and of near statistical significance in Pan troglodytes troglodytes, but not in older adults of those species; adults of Gorilla gorilla gorilla and Pongo pygmaeus are sexually dimorphic at all ages after dental maturity. The presence of sex-specific growth patterns in these hominoid taxa indicates a complex relationship between socioecological selective pressures and growth of the facial skeleton.     

Prezygapophyseal articular facet shape in the catarrhine thoracolumbar vertebral column

Two contrasting patterns of lumbar vertebral morphology generally characterize anthropoids. “Long‐backed” monkeys are distinguished from “short‐backed” apes [Benton: The baboon in medical research, Vol. 2 (1967:201)] with respect to several vertebral features thought to afford greater spinal flexibility in the former and spinal rigidity in the latter. Yet, discussions of spinal mobility are lacking important functional insight that can be gained by analysis of the zygapophyses, the spine's synovial joints responsible for allowing and resisting intervertebral movements. Here, prezygapophyseal articular facet (PAF) shape in the thoracolumbar spine of Papio, Hylobates, Pongo, Gorilla, and Pan is evaluated in the context of the “long‐backed” versus “short‐backed” model. A three‐dimensional geometric morphometric approach is used to examine how PAF shape changes along the thoracolumbar vertebral column of each taxon and how PAF shape varies across taxa at corresponding vertebral levels. The thoracolumbar transition in PAF shape differs between Papio and the hominoids, between Hylobates and the great apes, and to a lesser extent, among great apes. At the level of the first lumbar vertebra, the PAF shape of Papio is distinguished from that of hominoids. At the level of the second lumbar vertebra, there is variation to some extent among all taxa. These findings suggest that morphological and functional distinctions in primate vertebral anatomy may be more complex than suggested by a “long‐backed” versus “short‐backed” dichotomy. Am J Phys Anthropol 142:600–612, 2010. © 2010 Wiley‐Liss, Inc.     

Interspecific and Ontogenetic Variation in Proximal Pedal Phalangeal Curvature of Great Apes (Gorilla gorilla, Pan troglodytes, and Pongo pygmaeus)

Considerable attention has been devoted to understanding phalangeal curvature in primates, particularly with regard to locomotion. Previous work has found that increased phalangeal curvature may be indicative of increased grasping during suspensory and climbing behaviors, but the details of this relationship, particularly as regards feet, is still unclear. Using behavioral studies to predict an interspecific gradient of variation in pedal phalangeal curvature, I collected digital data from the third and fifth digit proximal pedal phalanges in adult Gorilla gorilla, Pan troglodytes, and Pongo pygmaeus and calculated included angles of phalangeal curvature to assess the appropriateness of pooling digits within taxa and evaluate the association between variation in pedal phalangeal curvature and frequency of climbing behavior. I also used an ontogenetic sample of Pan troglodytes to evaluate the postnatal relationship between variation in phalangeal curvature and grasping behaviors. I found intraspecific variation in phalangeal curvature suggesting among-digit variation in grasping behaviors. Curvature of Pongo was significantly greater than of both Pan and Gorilla. In contrast, Pan was significantly more curved than Gorilla only in comparison of third digits. Ontogenetic decreases in pedal phalangeal curvature among Pan troglodytes accorded well with postnatal decreases in documented climbing frequency. These findings largely support earlier work regarding the association between arboreal grasping and phalangeal curvature, and provide a unique intraspecific analysis that illuminates a number of areas where our knowledge of the behavioral and biomechanical determinants of phalangeal curvature should be explored further, particularly with respect to the role of among-digit variation in phalangeal curvature.     

Discrimination of extant Pan species and subspecies using the enamel–dentine junction morphology of lower molars

Previous research has demonstrated that species and subspecies of extant chimpanzees and bonobos can be distinguished on the basis of the shape of their molar crowns. Thus, there is potential for fossil taxa, particularly fossil hominins, to be distinguished at similar taxonomic levels using molar crown morphology. Unfortunately, due to occlusal attrition, the original crown morphology is often absent in fossil teeth, and this has limited the amount of shape information used to discriminate hominin molars. The enamel–dentine junction (EDJ) of molar teeth preserves considerable shape information, particularly in regard to the original shape of the crown, and remains present through the early stages of attrition. In this study, we investigate whether the shape of the EDJ of lower first and second molars can distinguish species and subspecies of extant Pan. Micro‐computed tomography was employed to non‐destructively image the EDJ, and geometric morphometric analytical methods were used to compare EDJ shape among samples of Pan paniscus (N = 17), Pan troglodytes troglodytes (N = 13), and Pan troglodytes verus (N = 18). Discriminant analysis indicates that EDJ morphology distinguishes among extant Pan species and subspecies with a high degree of reliability. The morphological differences in EDJ shape among the taxa are subtle and relate to the relative height and position of the dentine horns, the height of the dentine crown, and the shape of the crown base, but their existence supports the inclusion of EDJ shape (particularly those aspects of shape in the vertical dimension) in the systematic analysis of fossil hominin lower molars. Am J Phys Anthropol, 2009. © 2009 Wiley‐Liss, Inc.     

New pedal remains of Megaladapis and their functional significance

New remains of Megaladapis from the caves within the Ankarana Range of northern Madagascar and the cave site of Ankilitelo near Toliara in southwestern Madagascar add considerably to the present sample of pedal remains for this genus. Here we describe and analyze the new pedal material and discuss the function of the Megaladapis foot in terms of positional behavior and substrate use. The northern specimens belong to the M. madagascariensis/M. grandidieri group in terms of size and morphology, whereas the new southwestern fossils are assigned to M. madagascariensis. The new specimens demonstrate that the small and intermediate sized M. madagascariensis and M. grandidieri were very similar in anatomy and inferred locomotor function, findings that also support the prior suggestion that they belong to a single widespread subgenus (Megaladapis). The new fossils provide the first examples of many pedal elements and present the first opportunity to analyze the whole pedal complex from associated remains. The foot of Megaladapis is distinctive among primates in numerous features. Intrinsic proportions of the hindlimb indicate that the foot is relatively longer than that of any other primate. The first complete calcanei reveal a large and highly modified hindfoot. The calcaneus is reduced distally, indicating an emphasis on climbing over leaping or quadrupedal walking and running. Proximally, a large, medially directed calcaneal tuberosity suggests both a strong inversion component to plantarflexion and a well-developed abductor mechanism and recalls the calcaneal morphology of the larger lorisines in some respects. Talar shape is consistent with considerable tibial rotation during plantarflexion and dorsiflexion. The subtalar joint is designed to emphasize supination/pronation and medial/lateral rotation over proximodistal translation. The distal tarsals are extremely reduced in length, and they form a high transverse arch and a serial tarsus; this configuration promotes inversion/eversion at the transverse tarsal joint. The phalanges are long and moderately curved, and the hallux is very long, robust, and abducted. Pedal morphology suggests that Megaladapis (subgenus Megaladapis) was well adapted to exploit an arboreal environment. The grasping mechanism of Megaladapis is an extreme modification of the prosimian condition, emphasizing a highly inverted set, mobility in rotation, and a powerful abduction/flexion type grasp using large hallux and the lateral abductor musculature. Such a mechanism insures a secure grasp regardless of the position of the hindlimb or the substrate. These pedal design features contrast with the grasping strategy seen in highly arboreal palaeopropithecids (or “sloth lemurs”), a group that reduces and modifies the hindfoot, culminating in Palaeopropithecus, and emphasizes extrinsic digital flexors in a more hook-like mechanism. Much less is known of M. (Peloriadapis) edwardsi. The larger body size, more gorilla-like talar articular morphology, and anatomy of the proximal fifth metatarsal suggest that this species may have been more terrestrial than the smaller forms, but other aspects of pedal morphology suggest it also exploited arboreal habitats.     

Comparative histomorphology of intrinsic vibrissa musculature among primates: implications for the evolution of sensory ecology and “face touch”

Macrovibrissae are specialized tactile sensory hairs present in most mammalian orders, used in maxillary mechanoreception or “face touch.” Some mammals have highly organized vibrissae and are able to “whisk” them. Movement of vibrissae is influenced by intrinsic vibrissa musculature, striated muscle bands that attach directly to the vibrissa capsule. It is unclear if primates have organized vibrissae or intrinsic vibrissa musculature and it is uncertain if they can move their vibrissae. The present study used histomorphological techniques to compare vibrissae among 19 primates and seven non‐primate mammalian taxa. Upper lips of these mammals were sectioned and processed for histochemical analysis. While controlling for phylogenetic effects the following hypotheses were tested: 1) mammals with well‐organized vibrissae possess intrinsic vibrissa musculature and 2) intrinsic vibrissa musculature is best developed in nocturnal, arboreal taxa. Our qualitative analyses show that only arboreal, nocturnal prosimians possess intrinsic musculature. Not all taxa that possessed organized vibrissae had intrinsic vibrissa musculature. Phylogenetic comparative analyses revealed a 70% probability that stem mammals, primates, and haplorhines possessed intrinsic vibrissa musculature and well‐organized vibrissae. These two traits most likely coevolved according to a discrete phylogenetic analysis. These results indicate that nocturnal, arboreal primates have the potential to more actively use their vibrissae in spatial recognition and navigation tasks than diurnal, more terrestrial species, but there is a clear phylogenetic signal involved in the evolution of primate vibrissae and “face touch.” Am J Phys Anthropol, 2013. © 2012 Wiley Periodicals, Inc.     

The locomotion of Babakotia radofilai inferred from epiphyseal and diaphyseal morphology of the humerus and femur

Palaeopropithecids, or “sloth lemurs,” are a diverse clade of large‐bodied Malagasy subfossil primates characterized by their inferred suspensory positional behavior. The most recently discovered genus of the palaeopropithecids is Babakotia, and it has been described as more arboreal than Mesopropithecus, but less than Palaeopropithecus. In this article, the within‐bone and between‐bones articular and cross‐sectional diaphyseal proportions of the humerus and femur of Babakotia were compared to extant lemurs, Mesopropithecus and Palaeopropithecus in order to further understand its arboreal adaptations. Additionally, a sample of apes and sloths (Choloepus and Bradypus) are included as functional outgroups composed of suspensory adapted primates and non‐primates. Results show that Babakotia and Mesopropithecus both have high humeral/femoral shaft strength proportions, similar to extant great apes and sloths and indicative of forelimb suspensory behavior, with Babakotia more extreme in this regard. All three subfossil taxa have relatively large femoral heads, also associated with suspension in modern taxa. However, Babakotia and Mesopropithecus (but not Palaeopropithecus) have relatively small femoral head surface area to shaft strength proportions suggesting that hind‐limb positioning in these taxa during climbing and other behaviors was different than in extant great apes, involving less mobility. Knee and humeral articular dimensions relative to shaft strengths are small in Babakotia and Mesopropithecus, similar to those found in modern sloths and divergent from those in extant great apes and lemurs, suggesting more sloth‐like use of these joints during locomotion. Mesopropithecus and Babakotia are more similar to Choloepus in humerofemoral head and length proportions while Palaeopropithecus is more similar to Bradypus. These results provide further evidence of the suspensory adaptations of Babakotia and further highlight similarities to both extant suspensory primates and non‐primate slow arboreal climbers and hangers. J. Morphol. 277:1199–1218, 2016. © 2016 Wiley Periodicals, Inc.     

Locomotor behavior of Pan paniscus in Zaire

The locomotor behavior of Pan paniscus was studied over a four-week period in Equateur, Republic of Zaire. Bonobos were found to be both arboreal and terrestrial in their daily activities. In the trees adult bonobos are basically quadrupedal, but they also have significant components of armswinging, diving, leaping, and bipedalism in their locomotor repertoire.     

Ultrasonic Vocalizations of Six Taxa of Southern African Gerbils (Rodentia: Gerbillinae)

Ultrasonic calling during male-female encounters between individuals of the same species was investigated in six taxa of southern African gerbils, namely Tatera brantsii, Gerbillurus paeba paeba, G. p. cxilis, G. tytonis, G. setzeri, and G. vallinus. Vocalizations were detected by means of a bat detector utilizing a superheterodyne signal converter and a countdown circuit. Signals were recorded at audible frequencies and analysed with a sonograph. All taxa vocalized at ultrasonic frequencies by means of strongly modulated frequency “sweep” calls, which differed among taxa in duration, maximum and minimum frequency. “Clicks” were emitted by G. p. paeba and G. p. exilis, and G. tytonis emitted a “stutter” vocalization which consisted of a series of clicks. Long modulated “whistles” were identified from G. vallinus and T. brantsii at lower frequencies than “sweep” calls. Only one call type, a “sweep” call which differed in duration and frequency from all other taxa, was identified in G. setzeri. Cluster analysis was applied to the data using 7 acoustic characters. G. p. paeba and G. p. exilis displayed the highest similarity level between taxa and differed only in frequency of “sweep” vocalizations. G. paeba, G. tytonis and G. setzeri formed one cluster, while G. vallinus and T. brantsii formed a separate cluster. Numbers of calls in interspecific encounters were non-significantly less than in intraspecific encounters in all taxa except G. p. paeba, in which more vocalizations were recorded in inter- than intraspecific encounters. It is not clear whether species discrimination, measured by numbers of vocalizations in interspecific encounters, occurs.     

Evaluating the anesthetization and fixation efficacy of “soft” and “hard” freshwater benthic meiofauna: what is the best method for specimen preservation?

Sampling freshwater biological diversity is a challenge when it comes down to techniques for meiofauna fixation and preservation because this polyphyletic group of taxa is highly diverse. The aim of this study is to test the performance of three anesthetics (CO₂, MgCl₂ and low temperature) and three fixatives (formaldehyde 4 %; buffered formaldehyde 4 and 70 % ethanol) in the preservation of “soft” (gastrotrichs and rotifers) and “hard” (tardigrades and copepods) freshwater benthic meiofaunal assemblages. Due to these different morphological structures, we expected that treatment performance would vary among taxa in the quality of specimen fixation. Results revealed that the meiofaunal abundances of samples sorted alive or after the treatments with a coupling of anesthetics and fixatives were not different. However, preservation of specimens varied substantially among “soft” and “hard” meiofauna and among treatments. The use of 4 % buffered formaldehyde is highly recommended for freshwater meiofauna, while unbuffered formaldehyde should be avoided. Studies that have “soft” meiofauna as target organisms are recommended to use some type of anesthetic, although it is necessary to use a specific one for each taxon as they respond in different ways to different anesthetics.     

Spatial patterns and GIS habitat modelling of fish in two French Mediterranean coastal areas

The spring and summer distribution of adults and larval fish stages of Sparids and Scorpaenids was studied in two sites in the western Mediterranean. Fish adults and larvae of those two taxa were identified and sorted according to their life stages in order to study their distribution and develop suitable habitat maps. Study areas were located on French coastal waters, the “Côte Bleue” Marine Park (CBMP) has an east-west orientation with substratum dominated by Posidonia beds and the Marine Reserve of Cerbère-Banyuls (MRCB) runs north–south and is dominated by rocky substrates. Generalised Additive Models (GAM) combined with Geographic Information System (GIS), were used to model the suitable habitats for fish larvae and adults. During spring months, waters exhibit low Sea Surface Temperatures (SST), low Photosynthetically Active Radiation (PAR), high values of Sea Surface Chlorophyll-a concentration (Chl-a), and mostly negative values of Sea Level Anomaly (SLA) indicating anticyclonic eddies. During summer months, waters have higher values of SST, lower values of Chl-a and positive values of SLA indicating cyclonic eddies. The results revealed different environmental responses in the distribution of fish adults and larvae in the CBMP and MRCB. Suitable habitats for adult were mainly dependent on the substrate types (Posidonia meadows and sand) and they were found close to the coast, whereas fish larvae were dependent on environmental cues (Chl-a, SLA, SST) with a sparse spatial distribution.     

Ontogeny and the evolution of adult body size dimorphism in apes

This analysis investigates the ontogeny of body size dimorphism in apes. The processes that lead to adult body size dimorphism are illustrated and described. Potential covariation between ontogenetic processes and socioecological variables is evaluated. Mixed-longitudinal growth data from 395 captive individuals (representing Hylobates lar [gibbon], Hylobates syndactylus [siamang], Pongo pygmaeus [orangutan], Gorilla gorilla [gorilla], Pan paniscus [pygmy chimpanzee], and Pan troglodytes [“common” chimpanzee]) form the basis of this study. Results illustrate heterogeneity in the growth processes that produce ape dimorphism. Hylobatids show no sexual differentiation in body weight growth. Adult body size dimorphism in Pongo can be largely attributed to indeterminate male growth. Dimorphism in African apes is produced by two different ontogenetic processes. Both pygmy chimpanzees (Pan paniscus) and gorillas (Gorilla gorilla) become dimorphic primarily through bimaturism (sex differences in duration of growth). In contrast, sex differences in rate of growth account for the majority of dimorphism in common chimpanzees (Pan troglodytes). Diversity in the ontogenetic pathways that produce adult body size dimorphism may be related to multiple evolutionary causes of dimorphism. The lack of sex differences in hylobatid growth is consistent with a monogamous social organization. Adult dimorphism in Pongo can be attributed to sexual selection for indeterminate male growth. Interpretation of dimorphism in African apes is complicated because factors that influence female ontogeny have a substantial effect on the resultant adult dimorphism. Sexual selection for prolonged male growth in gorillas may also increase bimaturism relative to common chimpanzees. Variation in female growth is hypothesized to covary with foraging adaptations and with differences in female competition that result from these foraging adaptations. Variation in male growth probably corresponds to variation in level of sexual selection. © 1995 Wiley-Liss, Inc.