Plasma insulin-like growth factor-I,testosterone and morphological changes in the growth of captive agile gibbons ( Hylobates agilis) from birth to adolescence

We examined growth changes in concentrations of plasma insulin-like growth factor-1 (IGF-1) and testosterone, and somatometric parameters in two captive male agile gibbons from birth to about 4 years of age, to examine the evolution of growth patterns in primates. Plasma IGF-1 concentrations in agile gibbons generally increased with age with values ranging from 200 to 1,100 ng/ml. The growth profiles in plasma IGF-1 in the gibbons were similar to those reported for chimpanzees. The highest concentrations of plasma testosterone (230 and 296 ng/dl) were observed within the first 0.3 years from birth, then the concentrations rapidly decreased and fluctuated below 100 ng/dl. Continuously higher IGF-1 concentrations were observed after 2.6 and 3.5 years of age. The profiles of plasma testosterone in these gibbons also resembled those of other primates including humans. However, their plasma testosterone levels in both neonate and adult stages (60 ng/dl) were lower than those reported for macaques and chimpanzees of respective stages. The obtained growth profiles of plasma IGF-1 and testosterone suggest that the adolescent phase starts around 2.6 or 3.5 years of age in male agile gibbons. The growth trend in many morphological parameters including body weight showed a linear increase without a significant growth spurt at approximately the onset of puberty. Head length and first digit length had reached a plateau during the study period. Brachial index, which indicates the relative length of forearm to upper arm, significantly increased gradually through the growth period. This result indicates that forearm becomes relatively longer than the upper arm with growth, which may be an evolutionary adaptation for brachiation.     

Hormonal Correlates of Paternal Care Differences in the Hylobatidae

Only one of the 15 species of monogamous hylobatids, the siamang (Symphalangus syndactylus), demonstrates direct paternal care in the form of infant‐carrying, providing a unique model for examining hormonal correlates of paternal care differences between siamangs and gibbons. We used behavioral data and fecal hormone analysis to investigate (1) differences in monthly percent father–infant proximity in relation to monthly fecal androgen metabolite concentrations from infant birth to the late postpartum period between siamangs and gibbons, (2) the pattern of change in fecal androgen and fecal estrogen metabolite concentrations during the 8‐week peripartum period between siamangs and gibbons, and (3) the change in mean fecal glucocorticoid metabolite concentrations at 1‐month postpartum from individual baseline between siamangs and gibbons. Father–infant proximity increased as androgen concentrations decreased over the postpartum period in siamangs but not in gibbons. Androgen concentrations increased around birth in siamangs during the 8‐week peripartum period, but exhibited a decreasing trend around birth in gibbons. Estrogen concentrations increased from pre‐ to postpartum in siamangs during the 8‐week peripartum period, but exhibited a decreasing trend from pre‐ to postpartum in gibbons. The difference in mean glucocorticoid metabolite concentrations from baseline was greater in siamangs than gibbons. Our data suggest a relationship between specific steroid hormone patterns and differences in paternal care among the hylobatids, warranting further investigation of such proximate mechanisms.     

Uniqueness of primate forelimb posture during quadrupedal locomotion

Among the characteristics that are thought to set primate quadrupedal locomotion apart from that of nonprimate mammals are a more protracted limb posture and larger limb angular excursion. However, kinematic aspects of primate or nonprimate quadrupedal locomotion have been documented in only a handful of species, and more widely for the hind than the forelimb. This study presents data on arm (humerus) and forelimb posture during walking for 102 species of mammals, including 53 nonhuman primates and 49 nonprimate mammals. The results demonstrate that primates uniformly display a more protracted arm and forelimb at hand touchdown of a step than nearly all other mammals. Although primates tend to end a step with a less retracted humerus, their total humeral or forelimb angular excursion exceeds that of other mammals. It is suggested that these features are components of functional adaptations to locomotion in an arboreal habitat, using clawless, grasping extremities.     

Kinetic chain of overarm throwing in terms of joint rotations revealed by induced acceleration analysis

This study investigated how baseball players generate large angular velocity at each joint by coordinating the joint torque and velocity-dependent torque during overarm throwing. Using a four-segment model (i.e., trunk, upper arm, forearm, and hand) that has 13 degrees of freedom, we conducted the induced acceleration analysis to determine the accelerations induced by these torques by multiplying the inverse of the system inertia matrix to the torque vectors. We found that the proximal joint motions (i.e., trunk forward motion, trunk leftward rotation, and shoulder internal rotation) were mainly accelerated by the joint torques at their own joints, whereas the distal joint motions (i.e., elbow extension and wrist flexion) were mainly accelerated by the velocity-dependent torques. We further examined which segment motion is the source of the velocity-dependent torque acting on the elbow and wrist accelerations. The results showed that the angular velocities of the trunk and upper arm produced the velocity-dependent torque for initial elbow extension acceleration. As a result, the elbow joint angular velocity increased, and concurrently, the forearm angular velocity relative to the ground also increased. The forearm angular velocity subsequently accelerated the elbow extension and wrist flexion. It also accelerated the shoulder internal rotation during the short period around the ball-release time. These results indicate that baseball players accelerate the distal elbow and wrist joint rotations by utilizing the velocity-dependent torque that is originally produced by the proximal trunk and shoulder joint torques in the early phase.     

Quantitative and functional studies on the hands of the anthropoidea. I. The Hominoidea

The hands of the Hominoidea evidence four adaptive modes which distinguish the lesse apes (Hylobatidae), the orangutan (Pongo), the African apes (Pan), and man (Homo) from one another. The hands of the apes consist of compromises between manipulatory and locomotor functions because selection has operated for precision of grip as well as for special locomotor mechanisms. The human hand is almost totally devoted to manipulation. The hands of gibbons, orangutans and the African apes differ in many features that may be correlated with locomotion. The gibbons and siamang are specially adapted for ricochetal arm-swinging. The great apes possess morphological adaptations for arboreal foraging and climbing distinct from those of the hylobatids. In addition, the African apes have become secondarily adapted for terrestrial quadrupedal locomotion. Many features that distinguish the hands of chimpanzees and gorillas may be associated with the development of efficient knuckele-walking propulsive and support mechanisms.     

Biomechanical adaptation of ulnar cross-sectional morphology in brachiating primates

The forelimbs of hylobatids (gibbons and siamang) are distinctive among tetrapods in that they are loaded in overall tension during normal locomotion. While hylobatid ulnae must also encounter bending stresses in the course of their full range of locomotor behavior, their loading regime differs from that of quadrupedal anthropoids in that these bending stresses are distributed evenly along the bone, are not exerted in a preferred plane, and are probably of generally lower magnitude. This study examines the degree to which hylobatid ulnae are adapted to this suspensory loading regime. We obtained cross-sections of ulnae at various increments along the length of the bone using CAT scans. The sample comprises 476 cross-sections representing the ulnae of 25 individuals from five species of comparable body size. We show that in gibbons and siamang, the patterning of ulnar cross-sectional area and resistance to bending in the dorsoventral plane along the ulnar diaphysis differ from that of similarly sized quadrupedal anthropoids in the manner predicted by a suspensory loading regime. We also find the same pattern for the ulnae of Ateles, whose loading regime may be fairly similar to that of hylobatids. However, we find that the cross-sectional shape of the ulnar diaphysis in hylobatids and Ateles does not differ from that of quadrupedal monkeys in the manner predicted by a suspensory loading regime. © 1995 Wiley-Liss, Inc.     

Tube task hand preference in captive hylobatids

The link between laterality in humans and other primates is still hotly debated. Hylobatids have been rather neglected in this research area, yet they can provide important insights because: (1) they share with humans a complex vocal repertoire, which in humans is thought to be associated with brain hemispheric specialization and lateralized behaviors; (2) their adaptation to arboreality has produced unique postural constraints; (3) the little that is known about laterality in gibbons is contradictory (captive studies have provided conflicting results, while a field study on siamangs reported a population-level left-hand preference). To clarify this, we investigated hand preference in captive hylobatids [n = 42; 22 siamangs (Symphalangus syndactylus) and 20 gibbons (Hylobates sp., Nomascus leucogenys)] in nine Japanese facilities. We had a large sample size, controlled for possible confounds (posture, enclosure limitations) and used a well-established testing protocol (tube task). Handedness indices calculated from raw frequencies and bouts were highly correlated and showed a significant left-hand skew, which is consistent with data from wild siamangs. Major differences between captive and wild siamangs were a larger number of ambiguously handed individuals, and no significant age-related variation in captivity. The use of the index finger elicited a much more strongly lateralized response than the thumb. These results confirmed a left-hand preference in siamangs, but were equivocal in other hylobatids, and suggest selective pressures that may have acted on the highly arboreal hylobatids to favor handedness. Our study also indicates factors that might explain the discrepancy in the literature between handedness studies on captive and wild primate populations.     

“How pendulum‐like are siamangs? energy exchange during brachiation”

Hylobatidae (gibbons and siamangs) are known for their brachiation skills. The comparison of brachiation with a pendulum is made several times in the literature, and the costs and benefits of being pendulum-like are well described. However, the amount of energy exchange during brachiation of gibbons has rarely been determined. In this study, the amount of energy recovery (ER) during brachiation is assessed for three siamangs in a seminatural environment. The animals were recorded by four cameras while voluntarily brachiating on three different setups. The effects of locomotion speed, brachiation type, and setup on ER as well as on the external mechanical work during brachiation are determined. It is hypothesized that the amount of ER decreases with an increasing setup complexity while the external mechanical work increases. Additionally, we expect that support arm kinematics will be adjusted according to spatial complexity in order to maintain high recovery percentages. Our results show that ER is mainly determined by brachiation speed. Regardless of type of brachiation or setup, brachiation is done with a lower ER when brachiating faster. Within our limited range of setup variation, the expected effect of increasing complexity is not found. Although there is significant variation in support arm joint angles, no clear relation with speed, brachiation type, or setup is observed.     

EMG of chimpanzee shoulder muscles during knuckle-walking: problems of terrestrial locomotion in a suspensory adapted primate

By most accounts, the upper limb of the chimpanzee is primarily adapted to suspensory postures and locomotion. In order to determine how the derived morphology of the chimpanzee forelimb has affected the form of quadrupedal locomotion displayed by these animals, electromyographic activity patterns of 10 shoulder muscles during knuckle-walking in two chimpanzee subjects were analysed and compared to data on the opossum and cat taken from the literature. Telemetered electromyography coupled with simultaneous video recording was employed in order to study unfettered locomotion in the chimpanzee subjects.
Chimpanzees are characterized by a quadrupedal gait in which the hind limb overstrides the ipsilateral forelimb. Forelimb position in the plane of abduction/adduction is significantly affected by whether the hind limb passes inside or outside its ipsilateral forelimb. The degree of abduction adduction of the forelimb, in turn, influences many of the muscle activity patterns. That is, some muscles would be more frequently or less frequently active, depending on whether the arm was relatively abducted or adducted during a stride. Thus, there can be no single motor programme that generates the step cycle in chimpanzees.
While there are some parallels between muscle recruitment patterns for chimpanzee, opossum and cat quadrupedalism, the results of this study also indicate that many aspects of muscle use in chimpanzees have been significantly influenced by factors related to increased mobility of the upper limb. Finally, this study has revealed that moving the arm forward during swing phase of knuckle-walking is not a simple product of muscular elTort. and that other mechanisms must be involved. However, it is unclear at present exactly what these mechanisms may be.     

Climbing,brachiation, and terrestrial quadrupedalism: Historical precursors of hominid bipedalism

The vertical-climbing account of the evolution of locomotor behavior and morphology in hominid ancestry is reexamined in light of recent behavioral, anatomical, and paleontological findings and a more firmly established phylogeny for the living apes. The behavioral record shows that African apes, when arboreal, are good vertical climbers, and that locomotion during traveling best separates the living apes into brachiators (gibbons), scrambling/climbing/brachiators (orangutans), and terrestrial quadrupeds (gorillas and chimpanzees). The paleontological record documents frequent climbing as an ancestral catarrhine ability, while a reassessment of the morphology of the torso and forelimb in living apes and Atelini suggests that their shared unique morphological pattern is best explained by brachiation and forelimb suspensory positional behavior. Further, evidence from the hand and foot points to a terrestrial quadrupedal phase in hominoid evolution prior to the adoption of bipedalism. The evolution of positional behavior from early hominoids to hominids appears to have begun with an arboreal quadrupedal-climbing phase and proceeded though an orthograde, brachiating, forelimb-suspensory phase, which was in turn followed by arboreal and terrestrial quadrupedal phases prior to the advent of hominid bipedality. The thesis that protohominids climbed down from the trees to become terrestrial bipeds needs to be reexamined in light of a potentially long history of terrestriality in the ancestral protohominid. © 1996 Wiley-Liss, Inc.     

How close to a pendulum is human upper limb movement during walking?

The aim of this work was to investigate how close to pendulum-like behaviour the periodic motion of the human upper limb (or upper extremity) is, during normal walking at a comfortable speed of locomotion. Twenty-five healthy young persons (males and females) participated in the experiment. Biomechanical testing was undertaken (mass and centre of mass of each segment of the total upper extremity). Participants were walking on a treadmill with a standardised velocity of 1.1 ms(-1) (comfortable speed for all of them). A video analysis system with Silicon software was used to measure the different angles of the arm and forearm. The theoretical period of motion and maximal angular velocity were computed for the centre of mass of the total upper limb from the measured phases of the arm swing and associated positional potential energies. Actual measured periods of motion, in comparison, represented a level of similarity to a lightly damped simple pendulum. Using this assumption, the "damping factor" was calculated from the ratio between theoretical and measured values. A vast majority of people exhibited an actual angular velocity exceeding the expected theoretical angular velocity calculated for a virtual pendulum of similar mass and length characteristics. This may be due to muscle forces that are contributing to the motion of the upper limb during walking rather than simple gravity force acting alone. The observed positional potential energy of the dominant limb was greater than that of the non-dominant limb for the vast majority of participants.     

Comparisons of Suspensory Behaviors Among <Emphasis Type="Italic">Pygathrix cinerea</Emphasis>, <Emphasis Type="Italic">P. nemaeus</Emphasis>, and <Emphasis Type="Italic">Nomascus leucogenys</Emphasis> in Cuc Phuong National Park,Vietnam

In our study at the Endangered Primate Rescue Center of Cuc Phuong National Park, Vietnam, we aimed first to assemble a positional behavioral profile of captive gray-shanked (Pygathrix cinerea) and red-shanked (P. nemaeus) doucs that relates to the use of forelimb suspensory postures and arm-swinging locomotion. The profile is of interest because researchers have documented that red-shanked doucs more frequently use suspensory postures and locomotions than other colobines do. We confirmed that red-shanked doucs commonly use suspensory positional behaviors and also that gray-shanked doucs use suspensory behaviors at similar or even higher frequencies than those of red-shanked doucs. Our second goal was to assemble a preliminary kinematic profile of suspensory locomotion in Pygathrix within the context of the arm-swinging locomotion exhibited by northern white-cheeked gibbons, Nomascus leucogenys. Mean forelimb angles at initial contact and release of arm-swinging behaviors were remarkably consistent among gibbons and doucs despite the fact that gibbons typically used more continuous brachiation. Doucs also exhibit a greater range of forelimb angles than gibbons do. In addition, trunk orientation tends to be less vertical at initial contact for doucs than for gibbons, perhaps owing to the frequent use of quadrupedal sequences directly before or after forelimb suspension. Our behavioral and kinematic analyses add to the emerging realization that Pygathrix is capable of, and frequently expresses, a range of suspensory positional behaviors, including brachiation.     

Anatomy of the hominoid wrist joint: Its evolutionary and functional implications

Observations on the behavior of living hominoids show generic differences in the use and posture of the wrist joint. Both orang-utans and hylobatids usually use the wrist in suspensory behaviors. However, orang-utans emphasize markedly adducted and flexed wrist postures, while hylobatids emphasize violent forearm and wrist rotation. African apes, especially the gorilla, use the wrist more frequently than other hominoids for terrestrial quadrupedal weight-bearing. Humans use the wrist less frequently for supportive purposes than do other hominoids. These behavioral differences correspond to structural specializations in the proximal carpal joint of each of the hominoid genera. Although each of the hominoid genera has apparently modified its proximal carpal joint best to serve its characteristic behaviors, all hominoids share a unique proximal carpal joint that permits approximately 160ℴ of forearm rotation. The hylobatid proximal carpal joint is specialized in exhibiting a marked development of those structures limiting forearm rotation, but it is in most respects the least derived— that is, closest to the nonhominoid anthropoids. Chimpanzees show a proximal carpal joint that is more generalized than those of the other great apes but more derived than that of hylobatids. The human and gorilla proximal wrist joints, on the other hand, show marked modifications for weight-bearing in terrestrial behaviors. Orang-utans have the most derived proximal carpal joint, which in many respects parallels that of the slow-climbing nonhominoid primates. The comparative anatomy and structural specializations of the wrist joint support (a) an early divergence of hylobatids from the common hominoid stock, (b) a common ancestry for gorillas and humans separate from the other hominoids, and (c) a long independent evolutionary period for orang-utans since their divergence from the common hominoid stock, or one that was marked by strong selection pressures for wrist specializations. Unfortunately, the generalized condition of the chimpanzee’s wrist joint and the very derived condition of the orang-utan wrist provide uncertain evidence as to which of the two was first to diverge from the common hominoid stock. Identification of hominoid wrist specializations as reflecting real phylogenetic relationships or parallelisms depends on how well the phytogeny inferred from wrist morphology accords with those arrived at from the study of other systems.     

Fetlock joint kinematics differ with age in Thoroughbred [was thoroughbred] racehorses

Fetlock joint kinematics during galloping in 2-, 3-, 4-, and 5-year-old Thoroughbreds in race training were quantified to determine if differences due to age could account for the observation that 2-year old Thoroughbred racehorses incur a high number of injuries to the bones and soft tissues in the distal forelimbs during training and at the outset of racing. Twelve Thoroughbred racehorses were videotaped in the sagittal plane at 250 frames/s during their daily galloping workout on a 7/8 mile sand-surface training track. Four galloping strides were recorded for each horse and subsequently digitized to determine fetlock joint angles of the leading forelimb during the limb support period of a stride. Four kinematic variables were measured from each stride's angular profile: angle of fetlock joint dorsi-flexion at mid-stance, negative angular velocity, positive angular velocity and time from hoof impact to mid-stance phase of limb support. The 2-year old Thoroughbreds had significantly quicker rates of dorsi-flexion of their fetlock joints than 3- (p=0.01), 4- (p=0.01), and 5-year old (p<0.01) Thoroughbreds following impact of the leading forelimb during moderate galloping (avg. 14 m/s). Higher rates of dorsi-flexion in young Thoroughbreds may reflect immaturity (lack of stiffness) of the suspensory apparatus tissues.     

Morphological basis of arm-swinging: multivariate analyses of the forelimbs of Hylobates and Ateles

Field and laboratory studies of arm-swinging in gibbons reveal its singularity even compared to spider monkeys. On the basis of principal components and discriminant analyses of size-corrected forelimb variables, this study confirms their morphological uniqueness and the more generalized nature of the spider monkey forelimb. Long forearms, well-developed scapular spines, and sagittally thicker radial shafts are features associated strictly with gibbon arm-swinging. On the other hand, large humeral heads, projecting medial epicondyles, and axially elongated scapulae, traditionally regarded as arm-swinging traits, are probably more important for climbing.     

Changes in limb dynamics during the practice of rapid arm movements

In our study we examined Bernstein's hypothesis that practice alters the motor coordination among the muscular and passive joint moments. In particular, we conducted dynamical analyses of a human multisegmental movement during the practice of a task involving the upper extremity. Seven male human volunteers performed maximal-speed, unrestrained vertical arm movements whose upward and downward trajectories between two target endpoints required the hand to round a barrier, resulting in complex shoulder, elbow, and wrist joint movements. These movements were recorded by high-speed ciné film, and myopotentials from selected upper-extremity muscles were recorded. The arm was modeled as interconnected rigid bodies, so that dynamical interactions among the upper arm, forearm, and hand could be calculated. With practice, subjects achieved significantly shorter movement times. As movement times decreased, all joint-moment components (except gravity) increased, and the moment-time and EMG profiles were changed significantly. Particularly during reversals in movement direction, the changes in moment-time and EMG profiles were consistent with Bernstein's hypothesis relating practice effects and intralimb coordination: with practice, motor coordination was altered so that individuals employed reactive phenomena in such a way as to use muscular moments to counterbalance passive-interactive moments created by segment movements.     

Residual Upper Arm Motor Function Primes Innervation of Paretic Forearm Muscles in Chronic Stroke after Brain-Machine Interface (BMI) Training

Background

Abnormal upper arm-forearm muscle synergies after stroke are poorly understood. We investigated whether upper arm function primes paralyzed forearm muscles in chronic stroke patients after Brain-Machine Interface (BMI)-based rehabilitation. Shaping upper arm-forearm muscle synergies may support individualized motor rehabilitation strategies.

Methods

Thirty-two chronic stroke patients with no active finger extensions were randomly assigned to experimental or sham groups and underwent daily BMI training followed by physiotherapy during four weeks. BMI sessions included desynchronization of ipsilesional brain activity and a robotic orthosis to move the paretic limb (experimental group, n = 16). In the sham group (n = 16) orthosis movements were random. Motor function was evaluated with electromyography (EMG) of forearm extensors, and upper arm and hand Fugl-Meyer assessment (FMA) scores. Patients performed distinct upper arm (e.g., shoulder flexion) and hand movements (finger extensions). Forearm EMG activity significantly higher during upper arm movements as compared to finger extensions was considered facilitation of forearm EMG activity. Intraclass correlation coefficient (ICC) was used to test inter-session reliability of facilitation of forearm EMG activity.

Results

Facilitation of forearm EMG activity ICC ranges from 0.52 to 0.83, indicating fair to high reliability before intervention in both limbs. Facilitation of forearm muscles is higher in the paretic as compared to the healthy limb (p<0.001). Upper arm FMA scores predict facilitation of forearm muscles after intervention in both groups (significant correlations ranged from R = 0.752, p = 0.002 to R = 0.779, p = 0.001), but only in the experimental group upper arm FMA scores predict changes in facilitation of forearm muscles after intervention (R = 0.709, p = 0.002; R = 0.827, p<0.001).

Conclusions

Residual upper arm motor function primes recruitment of paralyzed forearm muscles in chronic stroke patients and predicts changes in their recruitment after BMI training. This study suggests that changes in upper arm-forearm synergies contribute to stroke motor recovery, and provides candidacy guidelines for similar BMI-based clinical practice.     

Restraint of Fgf8 signaling by retinoic acid signaling is required for proper heart and forelimb formation

Cardiomelic or heart–hand syndromes include congenital defects affecting both the forelimb and heart, suggesting a hypothesis where similar signals may coordinate their development. In support of this hypothesis, we have recently defined a mechanism by which retinoic acid (RA) signaling acts on the forelimb progenitors to indirectly restrict cardiac cell number. However, we still do not have a complete understanding of the mechanisms downstream of RA signaling that allow for the coordinated development of these structures. Here, we test the hypothesis that appropriate Fgf signaling in the cardiac progenitor field downstream of RA signaling is required for the coordinated development of the heart and forelimb. Consistent with this hypothesis, we find that increasing Fgf signaling can autonomously increase cardiac cell number and non-autonomously inhibit forelimb formation over the same time period that embryos are sensitive to loss of RA signaling. Furthermore, we find that Fgf8a, which is expressed in the cardiac progenitors, is expanded into the posterior in RA signaling-deficient zebrafish embryos. Reducing Fgf8a function in RA signaling-deficient embryos is able to rescue both heart and forelimb development. Together, these results are the first to directly support the hypothesis that RA signaling is required shortly after gastrulation in the forelimb field to temper Fgf8a signaling in the cardiac field, thus coordinating the development of the heart and forelimb.     

An Investigation of the Locomotor Function of Therian Forearm Pronation Provides Renewed Support for an Arboreal,Chameleon-like Evolutionary Stage

Although investigations of forelimb characteristics are central to therian evolutionary studies, the functional origins of forearm pronation are neglected. However, recent research based on bipedal manipulations strongly suggests that proximal radioulnar joint mobility is highly conserved in tetrapods. This new information calls for a replication of previously published physical simulations of forearm bone movements, to investigate whether active therian pronation/supination evolved from the plesiomorphic mechanism via which locomotor-induced torsion is passively alleviated during forelimb retraction. Preliminary results using representative extant and extinct tetrapod forelimb elements are supportive, and also offer insight into why another overlooked forearm trait, osteological full pronation (mechanically aligned elbow and wrist/finger joints), evolved only in therians and chameleons. During forelimb retraction in tetrapods with unfused radii/ulnae, the radius unexpectedly remains fixed in place as a functional complex with the firmly planted manus/carpus, which the ulnar complex (ulna/humerus) displaces relative to. Therefore, the highly conserved functional morphology of the tetrapod forearm indicates that enhanced therian manual dexterity, which emphasizes isolated radial movements bipedally, was preceded by the locomotor evolution of ulnar supination relative to the radius quadrupedally. This counterintuitive information indicates that the traditional hypothesis, that therian pronation/supination evolved arboreally to amplify radial mobility, requires modification. The authors propose that proximal long-axis rotations of the therian ulnar complex co-evolved with osteological full pronation during a period of arboreal, chameleon-like locomotion, to continue allowing torsion at a reinforced proximal radioulnar joint. These adaptations were later or simultaneously co-opted for object manipulation using active radioulnar pronation/supination.