A biomechanical perspective on the use of forelimb length as a measure of sexual selection in frogs

Differences in forelimb length between male and female frogs and between amplexing and non-amplexing males have been interpreted to be the results of sexual selection on forelimb length. The causal feature of the forelimb that has been posited to cause such selection is the observation that non-amplexing males attempt to disrupt breeding by prying amplexing males from females. A biomechanical model of forelimb function suggests that total length per se may not be the most appropriate measure to use. There are more functionally significant aspects of forelimb morphology, such as lever arm lengths, that should influence amplexing ability and may make measures of overall forelimb length misleading. This example highlights the relevance of functional analysis to current questions in evolutionary biology that rely on postulated roles for morphological structures under selection.     

The role of the forelimb in prey capture in the Late Triassic reptile Megalancosaurus (Diapsida,Drepanosauromorpha)

The pectoral girdle and forelimb of the Late Triassic drepanosauromorph reptile Megalancosaurus are redescribed and their function reinterpreted. The whole skeleton of this diapsid is highly specialised for arboreal life, and also the peculiarities of the shoulder girdle and forelimb were interpreted as adaptations for a limb-based locomotion using gap-bridging to move from one support to another, as in chameleons. Re-examination of the pectoral girdle and forelimb revealed the presence of clavicles fused into a furcula-like structure, a saddle-shaped glenoid and a tight connection between the radius and ulna that strengthened the forearm but hindered pronation and supination movements at that joint. The new information plus a reconstruction of the pectoral and forelimb musculature suggests that the forelimb was also specialised for grasping and raking in addition to climbing and thus prey capture may have been an important function for the forelimb. The new functional interpretation fits well with the overall body architecture of Megalancosaurus’ skeleton, suggesting that this reptile was an ambush predator that may have assumed a stable tripodal position, secured by the hooked tail and hind limbs, freeing its forelimbs to catch prey by sudden extension of the arm and firm grasping with the pincer-like digits.     

Morphometry of Macaca mulatta forelimb. II. Fiber-type composition in shoulder and elbow muscles

The present study examined the fiber-type proportions of 22 muscles spanning the shoulder and/or elbow joints of three Macaca mulatta. Fibers were classified as one of three types: fast-glycolytic (FG), fast-oxidative-glycolytic (FOG), or slow-oxidative (SO). In most muscles, the FG fibers predominated, but proportions ranged from 25-67% in different muscles. SO fibers were less abundant except in a few deep, small muscles where they comprised as much as 56% of the fibers. Cross-sectional area (CSA) of the three fiber types was measured in six different muscles. FG fibers tended to be the largest, whereas SO fibers were the smallest. While fiber-type size was not always consistent between muscles, the relative size of FG fibers was generally larger than FOG and SO fibers within the same muscle. When fiber CSA was taken into consideration, FG fibers were found to comprise over 50% of the muscle's CSA in almost all muscles.     

Wing morph-related physiological differences in adults of temperate population of Pyrrhocoris apterus (L.) (Heteroptera: Pyrrhocoridae)

The reproductive and diapausing adult females of brachypterous morph and macropterous females with reproductive arrest of non-diapause type, originating from the laboratory cultures of Pyrrhocoris apterus, were studied for their feeding and drinking behaviour, digestive enzyme activities, and carbohydrate and lipid contents. The highest feeding and drinking activities were observed in reproductive brachypters, the lowest in macropters. Macropters also differed from brachypters by lower activities of gut lipase, peptidase and protease, lower concentration of haemolymph sugars, and lower weight of fat body, which probably reflects their low feeding activity. The total content of fat body lipids was also lower in macropters (0.6 mg) than in reproductive and diapausing brachypters (4.6 and 7.5 mg, respectively) on day 14. A very high amount of glycogen was found in the fat body of diapausing brachypters, 363 μg on day 14, as opposed to 15 and 80 μg in macropterous and reproductive brachypterous females, respectively. The obtained data indicate that the most important difference between macropterous and brachypterous females with different types of reproductive arrest consists of an enhanced mobilization of lipids for dispersal in macropters and accumulation of energetic reserves for hibernation in brachypters.     

Analysis of forelimb function in basal ceratopsians

Here, I present the first study of forelimb function in basal ceratopsians [Correction added after publication 28 July 2007: in the preceding sentence 'Here, I present the first study of forelimb function in basal ceratopsians Dinosauria Orthischia ' was corrected to 'Here, I present the first study of forelimb function in basal ceratopsians']. I examined forelimb bones and casts of Psittacosaurus neimongoliensis , Psittacosaurus mongoliensis , Leptoceratops gracilis and Protoceratops andrewsi . For Ps. neimongoliensis and L. gracilis , I used manual manipulations of bones and casts to determine the range of motion at available forelimb joints. I then used range of motion and morphology to test the predictions of several hypotheses of forelimb function. Forelimb morphology and range of motion indicate that Psittacosaurus was an obligate biped and that Leptoceratops and Protoceratops were capable of quadrupedal locomotion. Forelimb mobility was too limited in Psittacosaurus for the hands to reach the mouth. Leptoceratops and Protoceratops are members of an evolutionary radiation in which an extension of the glenoid enabled the forelimbs to sprawl laterally for transverse pivoting, perhaps for display, but quadrupedal locomotion was accomplished with the elbows tucked in. In Protoceratops , the radius crosses over the ulna, causing the palms to face caudally. In Leptoceratops , the radius does not cross over the ulna; the palms face largely medially and the fingers have been reoriented so that flexion produces a caudal, propulsive force, even without caudally facing palms.     

FORELIMB FUNCTION IN ORNITHOLESTES HERMANNI OSBORN (DINOSAURIA, THEROPODA)

Abstract:  Ornitholestes hermanni is a Late Jurassic theropod dinosaur from North America. This kinematic study of Ornitholestes uses manual manipulations of forelimb casts to determine range of motion. The manual phalanges of the O. hermanni holotype, previously unidentified, are here identified as phalanges I-1, I-2 (ungual), II-2 and II-3 (ungual). At all represented manual joints, hyperextensibility is small or absent, whereas flexion is strong, as in most other theropods. The elbow can be strongly flexed beyond a right angle. When data on range of forelimb motion in Ornitholestes are added to such data from other theropods, high elbow flexion is present in maniraptoriform coelurosaurs but not in basal theropods. Forelimb functions requiring strong elbow flexion (such as holding objects to the chest, or tucking the forearms in for their protection or to reduce wind resistance or heat loss) were therefore available to maniraptoriform coelurosaurs but not to basal theropods.     

On the serial homology of the pectoral and pelvic girdles of tetrapods

While fore‐ and hindlimbs are commonly assumed to be serially homologous, the serial homology of the pectoral and pelvic girdles is more ambiguous. We investigate the degree to which a common history, developmental program, and gene network are shared between the girdles relative to the rest of the appendicular skeleton. Paleontological data indicate that pectoral appendages arose millions of years before pelvic appendages. Recent embryological and genetic data suggest that the anatomical similarity between the fore‐ and hindlimbs arose through the sequential, derived deployment of similar developmental programs and gene networks, and is therefore not due to ancestral serial homology. Much less developmental work has however been published about the girdles. Here, we provide the first detailed review of the developmental programs and gene networks of the pectoral and pelvic girdles. Our review shows that, with respect to these programs and networks, there are fewer similarities between pelvic and pectoral girdles than there are between the limbs. The available data therefore support recent hypotheses that the anatomical similarities between the fore‐ and hindlimbs arose during the fin‐to‐limb transition through the derived co‐option of similar developmental mechanisms, while the phylogenetically older pectoral and pelvic girdles have remained more distinct since their evolutionary origin.     

Associated cranial and forelimb remains attributed to Australopithecus afarensis from Hadar, Ethiopia

A partial skeleton from Hadar, Ethiopia (A.L. 438-1) attributed to Australopithecus afarensis is comprised of part of the mandible, a frontal bone fragment, a complete left ulna, two second metacarpals, one third metacarpal, plus parts of the clavicle, humerus, radius, and right ulna. It is one of only a few early hominin specimens to preserve both cranial and postcranial elements. It also includes the first complete ulna from a large A. afarensis individual, and the first associated metacarpal and forelimb remains. This specimen, dated to approximately 3Ma, is among the geologically youngest A. afarensis fossils and is also one of the largest individuals known. Its ulnar to mandibular proportions are similar to those of the geologically older and much smaller A.L. 288-1, suggesting that body size increased without disproportional enlargement of the mandible. Overall, however, analysis of this large specimen and of the diminutive A.L. 288-1 demonstrates that the functional morphology of the A. afarensis upper limb was similar at all body sizes; there is no evidence to support the hypothesis that more than one hominin species is present at Hadar. Morphologically, all apparent apomorphic traits of the elbow, forearm, wrist, and hand of A.L. 438-1 are shared uniquely with humans. Compared to humans, A.L. 438-1 does have a more curved ulna, although A.L. 288-1 does not, and it appears to have had slightly less well-developed manipulatory capabilities of its hands, although still more derived than in apes. We conclude that selection for effective arboreality in the upper limb of Australopithecus afarensis was weaker than in non-hominins, and that manipulative ability was of greater selective advantage than in extant great apes.     

Functional diversity for body actions in the mesencephalic locomotor region

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