Forelimb Anatomy Research Articles

Evidence at hand: Diversity, functional implications, and locomotor prediction in intrinsic hand proportions of diprotodontian marsupials

Knowledge about the diversity, locomotor adaptations, and evolution of the marsupial forelimb is limited, resulting in an underrepresentation of marsupials in comparative anatomical literature on mammalian forelimb anatomy. This study investigated hand proportions in the diverse marsupial order Diprotodontia. Fifty-two measurements of 95 specimens representing 47 species, as well as 6 non-diprotodontian specimens, were explored using principal components analysis (PCA). Bootstrapping was used to assess the reliability of the loadings. Phylogenetically independent contrasts and phylogenetic ANOVA were used to test for correlation with size and functional adaptation of forelimbs for locomotor habit, scored as arboreal vs. terrestrial. Analysis of first principal component (PC1) scores revealed significant differences between arboreal and terrestrial species, and was related to relative slenderness of their phalangeal elements. Both locomotor groups displayed allometry along PC1 scores, but with different intercepts such that PC1 discriminated between the two locomotor habits almost completely. PC2 separated some higher-level clades and burrowing species. Analysis of locomotor predictors commonly applied by palaeontologists indicates that ratios between proximal and intermediate phalanges were unsuitable as predictors of arboreality/terrestriality, but the phalangeal index was more effective. From PCA results, a phalangeal slenderness ratio was developed which proved to be a useful discriminator, suggesting that a single unallocated phalanx can be used for an impression of locomotor mode in fossils. Most Diprotodontia are laterally paraxonic or ectaxonic, with the exception of digging species whose hands are medially paraxonic. Our results complement those of studies on placental mammals, suggesting that the demands of arboreality, terrestriality, or frequent digging on intrinsic hand proportions are met with similar anatomical adaptations in marsupials.

It's not all in the hips: Crocodylian forelimb anatomy and evolution

It's not all in the hips: Crocodylian forelimb anatomy and evolution

Crocodylian forelimb musculature and its relevance to Archosauria.

The musculoskeletal anatomy of the crocodylian forelimb is documented to facilitate functional morphological studies of extant and extinct archosaurs. Comparative descriptions of muscles of the forelimb of several crocodylian species are presented, including attachment sites, innervation, and anatomical functions. The muscular anatomy of the crocodylian forelimb is highly conservative among the different species; however, interspecific differences do occur. Interspecific anatomical variation is interpreted functionally, and discussed in the context of the terrestrial locomotion of crocodylians as it applies to the forelimb. In addition, muscular apomorphies are identified among a phylogenetically diverse sample of extant crocodylians, providing insight into the evolution of forelimb anatomy in a clade of archosaurs possessing highly variable terrestrial locomotor behaviors.

The effect of gait and digital flexor muscle activation on limb compliance in the forelimb of the horse Equus caballus.

A horse's legs are compressed during the stance phase, storing and then returning elastic strain energy in spring-like muscle-tendon units. The arrangement of the muscle-tendon units around the lever-like joints means that as the leg shortens the muscle-tendon units are stretched. The forelimb anatomy means that the leg can be conceptually divided into two springs: the proximal spring, from the scapula to the elbow, and the distal spring, from the elbow to the foot. In this paper we report the results of a series of experiments testing the hypothesis that there is minimal scope for muscle contraction in either spring to adjust limb compliance. Firstly, we demonstrate that the distal, passive leg spring changes length by 127 mm (range 106-128 mm) at gallop and the proximal spring by 12 mm (9-15 mm). Secondly, we demonstrate that there is a linear relationship between limb force and metacarpo-phalangeal (MCP) joint angle that is minimally influenced by digital flexor muscle activation in vitro or as a function of gait in vivo. Finally, we determined the relationship between MCP joint angle and vertical ground-reaction force at trot and then predicted the forelimb peak vertical ground-reaction force during a 12 m s(-1) gallop on a treadmill. These were 12.79 N kg(-1) body mass (BM) (range 12.07-13.73 N kg(-1) BM) for the lead forelimb and 15.23 N kg(-1) BM (13.51-17.10 N kg(-1) BM) for the non-lead forelimb.

Mediolateral reaction forces and forelimb anatomy in quadrupedal primates: implications for interpreting locomotor behavior in fossil primates.

The forelimb joints of terrestrial primate quadrupeds appear better able to resist mediolateral (ML) shear forces than those of arboreal quadrupedal monkeys. These differences in forelimb morphology have been used extensively to infer locomotor behavior in extinct primate quadrupeds. However, the nature of ML substrate reaction forces (SRF) during arboreal and terrestrial quadrupedalism in primates is not known. This study documents ML-SRF magnitude and orientation and forelimb joint angles in six quadrupedal anthropoid species walking across a force platform attached to terrestrial (wooden runway) and arboreal supports (raised horizontal poles). On the ground all subjects applied a lateral force in more than 50% of the steps collected. On horizontal poles, in contrast, all subjects applied a medially directed force to the substrate in more than 75% of the steps collected. In addition, all subjects on arboreal supports combined a lower magnitude peak ML-SRF with a change in the timing of the ML-SRF peak force. As a result, during quadrupedalism on the poles the overall SRF resultant was relatively lower than it was on the runway. Most subjects in this study adduct their humerus while on the poles. The kinetic and kinematic variables combine to minimize the tendency to collapse or translate forelimbs joints in an ML plane in primarily arboreal quadrupedal primates compared to primarily terrestrial quadrupedal ones. These data allow for a more complete understanding of the anatomy of the forelimb in terrestrial vs. arboreal quadrupedal primates. A better understanding of the mechanical basis of morphological differences allows greater confidence in inferences concerning the locomotion of extinct primate quadrupeds.

Eurotamandua and Palaeanodonta: convergent or related?

Middle EoceneEurotamandua from Germany has been considered to be the oldest anteater and the only known Old World xenarthran, based on numerous derived features shared with living Myrmecophagidae or Xenarthra. Many of these features are ambiguous, however, and comparison with early Tertiary Palaeanodonta reveals several detailed, derived resemblances in forelimb anatomy. This suggests thatEurotamandua may be descended from, or the sister taxon of, Palaeanodonta.

Comparative myology of the forelimb of squirrels (Sciuridae)

The musculature of the shoulder, arm, and forearm was studied in 19 genera of squirrels, representing the Pteromyinae (flying squirrels) and all 7 tribes of the Sciurinae (tree and ground squirrels). The objective was to locate derived anatomical features of functional or phylogenetic significance and to determine how much morphological variation underlies the diverse locomotor behavior of squirrels, which includes terrestrial and arboreal bounding, climbing, digging, and gliding. The fossil evidence suggests that arboreality is primitive for squirrels, and in fact tree squirrels appear to represent the primitive sciurid morphology. Ground squirrels are less uniform and exhibit a few derived features, including a clavobrachialis muscle not seen in other squirrels. Pygmy tree squirrels, which have evolved independently in three tribes, exhibit convergence of forelimb anatomy, including the loss or reduction of several muscles in the shoulder and forearm. The forelimb anatomy of flying squirrels is the most derived and differs from that of tree squirrels in details of shoulder, arm, and forearm musculature. Some of these muscular differences among squirrels have phylogenetic significance, being shared by closely related genera, but none has significance above the tribal level. Many of the differences suggest a variety of changes in function that are amenable to further study. J. Morphol. 234:155–182, 1997. © 1997 Wiley-Liss, Inc.

Forelimb musculature and ligaments in Ateles, the spider monkey.

The forelimb anatomy of Ateles, the spider monkey, is a key factor in its locomotor adaptation because of its extensive use of bimanual suspensory locomotion in addition to climbing and quadrupedal walking (Mittermeier, 1978; and Fleagle and Mittermeier, 1980). The detailed description of the muscles and ligaments of the forelimb of Ateles provided in this paper can be of considerable use not only to primate morphologists interested in both extant and fossil primates but also to functional anatomists. All measurements were made on fresh, unembalmed specimens. Standard anatomical descriptions of the musculature, cross-sectional areas of the muscles, dry weights of muscle bellies, and relative proportions of antagonistic muscles are reported as are the joint ligaments and potential range of motions of the joints. These anatomical data are compared briefly to published data on Alouatta, the howler monkey, which is predominantly a quadruped (Fleagle and Mittermeier, 1980; and Schön Ybarra, 1982).

Functional implications of felid forelimb anatomy

The elbow and wrist anatomy of 17 felid species were studied and compared with that of other representative mammaliam carnivores. Based on the shape and position of the olecranon fossa, it was determined that for felids the forelimb cannot travel in a "pendulum-like" motion during locomotion, but must travel through an arch away from the parasagittal plane of the body. For the anterior limb, the degree of deviation from the parasagittal plane was correlated with habitat preference. In this regard, those felids that are exclusive forest dwellers (found exclusively in high, densely structured habitats) had the greatest angle of inclination of the olecranon fossa. In addition, these, species had a large lateral olecranon tuberosity for the attachment of the lateral head of the triceps muscle. For those felids that inhabit more open terrain (low-structured habitat), the olecranon fossa was less inclined, the medical olecranon tuberosity relatively large, and the medial head of the triceps was significantly heavier than those of the forest felids. Both the wrist and elbow joints exhibited a large degree of mobility which was reflective of the claw-equipped forelimb being used as a hunting weapon.

Structural correlates of forelimb function in fur seals and sea lions.

Dissections, manipulation of ligamentary preparations, analysis of limb proportions, and quantitative aspects of forelimb myology are used to correlate forelimb morphology in fur seals and sea lions (sub-family Otariinae) with previously published data as to their locomotor function (English, '76a). Comparisons to structure and function in generalized fissiped carnivores are then used to elucidate locomotor adaptations in fur seals and sea lions. Unique features of forelimb function during swimming in these pinnipeds include the amounts of abduction-adduction and rotary movements used. Modifications of the size, attachments and fasicle architecture of the muscles and the structure and range of possible movement of the joints suggest that in fur seals and sea lions these movements (1) take place about the glenohumeral (shoulder) joints, (2) that the movements are probably finely controlled, and (3) that they contribute to the generation of massive forward thrust via the cooperative activity of muscles capable of generating large amounts of force throughout the range of movement. Recovery movements occur through a similarly large range, and modifications of forelimb anatomy either to minimize or overcome water resistance are noted. The adaptive significance of these modifications is interpreted as allowing fur seals and sea lions to swim at speeds necessary to feed on the fast swimming prey presumably abundant in their adaptive zone.