Locomotor behavior and skeletal morphology of two sympatric pitheciine monkeys,Pithecia pithecia and Chiropotes satanas

Field observations of two sympatric pitheciine species reveal that the positional repertoire of the white-faced saki, Pithecia pithecia, is dominated by leaping behaviors, whereas the bearded saki, Chiropotes satanas, is predominantly quadrupedal. Examination and comparison of the postcranial skeletal morphologies and limb proportions of these species display numerous features associated with their respective locomotor behaviors. These observations accord with associations found in other primate and mammalian groups and with predictions based on theoretical and experimental biomechanics. Preliminary observations of the skeletal morphology of Cacajao calvus demonstrate a marked similarity to that of Chiropotes. The fossil platyrrhine Cebupithecia sarmientoi displays greater similarity to Pithecia, suggesting that its positional repertoire also included significant leaping and clinging behaviors.     

A unified theory for the energy cost of legged locomotion

Small animals are remarkably efficient climbers but comparatively poor runners, a well-established phenomenon in locomotor energetics that drives size-related differences in locomotor ecology yet remains poorly understood. Here, I derive the energy cost of legged locomotion from two complementary components of muscle metabolism, Activation–Relaxation and Cross-bridge cycling. A mathematical model incorporating these costs explains observed patterns of locomotor cost both within and between species, across a broad range of animals (insects to ungulates), for a wide range of substrate slopes including level running and vertical climbing. This ARC model unifies work- and force-based models for locomotor cost and integrates whole-organism locomotor cost with cellular muscle physiology, creating a predictive framework for investigating evolutionary and ecological pressures shaping limb design and ranging behaviour.     

Ecological associations of autopodial osteology in Neotropical geckos

Coevolution of form and function inspires investigation of associations between morphological variation and the exploitation of specific ecological settings. Such relationships, based mostly on traits of external morphology, have been extensively described for vertebrates, and especially so for squamates. External features are, however, composed by both soft tissues and bones, and these likely play different biomechanical roles during locomotion, such as in the autopodia. Therefore, ecological trends identified on the basis of external morphological measurements may not be directly correlated with equivalent variation in osteology. Here, we investigate how refined parameters of autopodial osteology relate to ecology, by contrasting climbing and nonclimbing geckos. Our first step consisted of inferring how external and osteological morphometric traits coevolved in the group. Our results corroborate the hypothesis of coevolution between external and osteological elements in the autopodia of geckos, and provides evidence for associations between specific osteological traits and preferred locomotor habit. Specifically, nonclimbers exhibit longer ultimate and penultimate phalanges of Digit V in the manus and pes and also a longer fifth metatarsal in comparison with climbers, a pattern discussed here in the context of the differential demands made upon locomotion in specific ecological contexts. Our study highlights the relevance of osteological information for discussing the evolution of ecological associations of the tetrapod autopodium. J. Morphol. 278:290–299, 2017. © 2017 Wiley Periodicals, Inc.     

Pendular mechanics and the kinematics and energetics of brachiating locomotion

Because brachiating locomotion is characterized by a pattern of swinging movements, brachiation has often been analogized to pendular motion, and aspects of the mechanics of pendular systems have been used to provide insight into both energetic and structural design aspects of this locomotor mode. However, there are several limitations to this approach. First, the motions of brachiating animals only approximate pendular motion, and therefore the energetics of these two systems are only roughly comparable. Second, the kinematic similarity between brachiation and pendular motion will be maximal at only one velocity, and the correspondence will be even less at greater or lesser speeds. Third, all forms of terrestrial locomotion that involve the use of limbs incorporate elements of pendular systems, and therefore brachiation is not unusual in this respect. Finally, it has been suggested that the mechanics of pendular motion will constrain the maximum attainable body size of brachiating animals and that this mechanical situation explains the lack of brachiating primates of greater than 30-kg body size; the present analysis provides evidence that the constraints on body size are far less strict than previously indicated and that extrinsic factors such as the geometry of the forest environment are more likely to dictate maximum body size for brachiators.     

Fast axon activity and the motor pattern in cockroach legs during swimming

Abstract Electromyographic recordings were made from muscles that extend the trochanter/femur of each of the six legs of American cockroaches, Periplaneta americana (L.), while the insects swam in water. The recordings showed two novel features. (1) During swimming, muscle activity in different legs was coordinated in the alternating tripod pattern commonly seen during free walking on land, not in the pattern of synchronous leg pairs common to other large terrestrial insects in water. (2) Fast axons were usually recruited along with slow axons, even when the insect swam at a moderate pace. Fast axon activity always started after the middle of the slow axon burst in intact insects, but vanished from most bursts in the stump of the leg after amputation of the femur. The alternating tripod pattern was maintained even after amputation. Possible causes of fast axon recruitment are discussed.     

Behavioural variation in natural populations. V. Morphological correlates of locomotion in the garter snake (Thamnophis radix)

A series of morphologieal and locomotor performance variables was measured in a population of newborn garter snakes to determine whether performance capacity has a significant morphological basis in these animals. Morphological traits measured were body length and mass, number of body and tail vertebrae and numbers of vertebral abnormalities. Locomotor performances included burst and mid-distance speed and distance and time crawled before anti-predator displays were assumed. All performance variables were repeatable in daily replicate trials ( P < 0.001). Individual burst speed, mid-distance speed, and distance crawled were significantly correlated pairwise ( P < 0.01). Most morphological and performance variables had a significant mass dependence (static allometry), although the effects were rather weak ( r ² < 0.1, except for body length): larger animals performed better and had fewer abnormalities. There were significant associations between some morphological traits and locomotor performance. Morphological factors accounted for 19% of the variation in mid-distance speed and 14% of the variation in antipredator behavior by multiple regression analysis. Canonical correlation of all performance and morphological variables simultaneously accounted for 24% of the observed variation in performance. Numbers of body and tail vertebrae (assayed by scale counts) had an interactive effect on speed of locomotion.     

A new hominoid hamate and first metacarpal from the Late Miocene Nagri Formation of Pakistan

A hamate and the proximal part of a first metacarpal from the type locality of the Nagri Formation in Pakistan, and attributed to Sivapithecus parvada, are described. In overall proportions, the hamate is rather robust, showing most similarity to that of Gorilla. Unlike extant hominoids it lacks a well-developed hamulus, and its triquetral facet is morphologically dissimilar to that in extant anthropoids. The morphology of the hamate indicates effective weight transmission through the ulnar side of the wrist, limited ulnar deviation and restricted extension in the triquetrohamate joint, and stability of the hamatometacarpal joints. The morphology of the partial first metacarpal is most similar to that of Pan. Previously described postcranial bones of S. parvada indicate that its locomotor behaviour included both quadrupedalism and climbing. This is consistent with the limited evidence of the first metacarpal, whereas the hamate strongly emphasizes the quadrupedal aspect of the locomotor repertoire.     

Steady state terrestrial ecosystems and the global carbon cycle

The assumption that landscapes dominated by mature vegetation are presently in carbon steady state with the atmosphere is challenged. Evidence suggests that the vegetation and soils of these landscapes are frequently disturbed and over short time periods (<300 yr) slowly sequester atmospheric carbon. The critical consideration in this argument is the time interval used to evaluate a steady state. Current models of carbon flux through the terrestrial biota limit their time considerations to 120 yr, a short and inadequate time interval for realistic assumptions about steady state in the carbon cycle of vegetation.Research performed under subcontract 19B-07762C with S. Brown and 19X-43326C with the Center for Energy and Environment Research of the University of Puerto Rico (A. E. Lugo) under Martin Marietta Energy Systems, Inc., contract DE-AC05-840R21400 with the U.S. Department of Energy.     

The postcranial skeleton of Kingoria nowacki (von Huene) (Therapsida: Dicynodontia)

A new specimen of Kingoria nowacki (von Huene) with a complete pelvic girdle and hindlimb is reconstructed and the method of locomotion analysed. It is concluded that the hindlimb was modified from the normal dicynodont pattern in a direction comparable to that of advanced mammal-like reptiles which are presumed to have given rise to mammals. The pectoral girdle also had a modified form, but the humerus was probably conservative in its morphology. The hindlimb stride relied on protraction and retraction to effect movement while the forelimb relied on long axis rotation of the humerus. Possible reasons for the difference in morphology and function of the fore-and hindlimbs are discussed, and a functional sequence for the generation of the Kingoria pelvic girdle from that of other Permian dicynodonts is suggested.