A potential role for bat tail membranes in flight control

Wind tunnel tests conducted on a model based on the long-eared bat Plecotus auritus indicated that the positioning of the tail membrane (uropatagium) can significantly influence flight control. Adjusting tail position by increasing the angle of the legs ventrally relative to the body has a two-fold effect; increasing leg-induced wing camber (i.e., locally increased camber of the inner wing surface) and increasing the angle of attack of the tail membrane. We also used our model to examine the effects of flying with and without a tail membrane. For the bat model with a tail membrane increasing leg angle increased the lift, drag and pitching moment (nose-down) produced. However, removing the tail membrane significantly reduced the change in pitching moment with increasing leg angle, but it had no significant effect on the level of lift produced. The drag on the model also significantly increased with the removal of the tail membrane. The tail membrane, therefore, is potentially important for controlling the level of pitching moment produced by bats and an aid to flight control, specifically improving agility and manoeuvrability. Although the tail of bats is different from that of birds, in that it is only divided from the wings by the legs, it nonetheless, may, in addition to its prey capturing function, fulfil a similar role in aiding flight control.     

Coevolution of caudal skeleton and tail feathers in birds

Birds are capable of a wide range of aerial locomotor behaviors in part because of the derived structure and function of the avian tail. The tail apparatus consists of a several mobile (free) caudal vertebrae, a terminal skeletal element (the pygostyle), and an articulated fan of tail feathers that may be spread or folded, as well as muscular and fibroadipose structures that facilitate tail movements. Morphological variation in both the tail fan and the caudal skeleton that supports it are well documented. The structure of the tail feathers and the pygostyle each evolve in response to functional demands of differing locomotor behaviors. Here, I test whether the integument and skeleton coevolve in this important locomotor module. I quantified feather and skeletal morphology in a diverse sample of waterbirds and shorebirds using a combination of linear and geometric morphometrics. Covariation between tail fan shape and skeletal morphology was then tested using phylogenetic comparative methods. Pygostyle shape is found to be a good predictor of tail fan shape (e.g., forked, graduated), supporting the hypothesis that the tail fan and the tail skeleton have coevolved. This statistical relationship is used to reconstruct feather morphology in an exemplar fossil waterbird, Limnofregata azygosternon. Based on pygostyle morphology, this taxon is likely to have exhibited a forked tail fan similar to that of its extant sister clade Fregata, despite differing in inferred ecology and other aspects of skeletal anatomy. These methods may be useful in reconstructing rectricial morphology in other extinct birds and thus assist in characterizing the evolution of flight control surfaces in birds. J. Morphol. 275:1431–1440, 2014. © 2014 Wiley Periodicals, Inc.     

Flight mechanics of a tailless articulated wing aircraft

This paper investigates the flight mechanics of a micro aerial vehicle without a vertical tail in an effort to reverse-engineer the agility of avian flight. The key to stability and control of such a tailless aircraft lies in the ability to control the incidence angles and dihedral angles of both wings independently. The dihedral angles can be varied symmetrically on both wings to control aircraft speed independently of the angle of attack and flight path angle, while asymmetric dihedral can be used to control yaw in the absence of a vertical stabilizer. It is shown that wing dihedral angles alone can effectively regulate sideslip during rapid turns and generate a wide range of equilibrium turn rates while maintaining a constant flight speed and regulating sideslip. Numerical continuation and bifurcation analysis are used to compute trim states and assess their stability. This paper lays the foundation for design and stability analysis of a flapping wing aircraft that can switch rapidly from flapping to gliding flight for agile manoeuvring in a constrained environment.     

Electromyographic and kinematic studies of tail movements during falling in cats

When falling from an inverted position, EMG activities of tail muscles (the m. extensor caudae lateralis, m. abductor caudae externus, m. flexor caudae longus) and tail movements were recorded in 7 long-tailed adult cats. After being released from an elevated position, cat rotates the tail in a reverse direction to rotation of other parts of the cat's body then lands on four legs. Rotation of the tail was started by EMG activities of the tail muscles on one side. Both synchronized and alternating groups of discharge occur between its left and right side, while extensor and flexor movements and displacements of its tail appear in the air. After transection of ventral roots from the coccygeal spinal segments innervating tail muscles, cats often fail to land on four legs. These facts suggest that that tail movements control body balance in the air when falling from an inverted position.     

Ultrastructural study and ontogenesis of the appendages and related musculature of Paraspadella (Chaetognatha)

A lineage of benthic chaetognaths has developed limb-like appendages on the caudal part of the body, resulting from a local modification of the lateral fins, which are folds of the epidermis and have a role in balance when swimming. The most complex are those of Paraspadella gotoi which are used as props with the tip of the tail, allowing an elaborated mating behaviour comprising different movements: complete erection of the body, swings and jumps, astonishing for so simple-bodied animals. In the tail, the epidermis and the connective tissue, together with the longitudinal musculature, are involved in this innovation. All the components of the fins, i.e. connective tissue, fin rays and multilayered epidermic cells are conserved, but their function has changed. The movements of appendages are adjusted by one pair of small appendicular muscles localised in the body wall, while posture movements of the body are allowed by four longitudinal bundles of raising muscle. These two new muscles have successively appeared in the evolutive series previously described in Paraspadella. They have definitely arisen from the secondary muscle: the two lateral bundles for the former, and the two dorsal and two ventral ones for the latter. All are supercontracting muscles, a muscle kind also observed in the other benthic genus Spadella, but unknown in planktonic and benthoplanktonic chaetognaths.     

Expression patterns of leg genes in the mouthparts of the spider<Emphasis Type="Italic"> Cupiennius salei</Emphasis> (Chelicerata: Arachnida)

The leg genes extradenticle, homothorax, dachshund, and Distal-less define three antagonistic developmental domains in the legs, but not in the antenna, of Drosophila. Here we report the expression patterns of these leg genes in the prosomal appendages of the spider Cupiennius salei. The prosoma of the spider bears six pairs of appendages: a pair of cheliceres, a pair of pedipalps, and four pairs of walking legs. Three types of appendages thus can be distinguished in the spider. We show here that in the pedipalp, the leg-like second prosomal appendage, the patterns are very similar to those in the legs themselves, indicating the presence of three antagonistic developmental domains in both appendage types. In contrast, in the chelicera, the fang-like first prosomal appendage, the patterns are different and there is no evidence for antagonistic domains. Together with data from Drosophila this suggests that leg-shaped morphology of arthropod appendages requires an underlying set of antagonistic developmental domains, whereas other morphologies (e.g. antenna, chelicera) may result from the loss of such antagonistic domains.Edited by M. Akam     

Three-Dimensional Reconstructions Come to Life – Interactive 3D PDF Animations in Functional Morphology

Digital surface mesh models based on segmented datasets have become an integral part of studies on animal anatomy and functional morphology; usually, they are published as static images, movies or as interactive PDF files. We demonstrate the use of animated 3D models embedded in PDF documents, which combine the advantages of both movie and interactivity, based on the example of preserved Trigonopterus weevils. The method is particularly suitable to simulate joints with largely deterministic movements due to precise form closure. We illustrate the function of an individual screw-and-nut type hip joint and proceed to the complex movements of the entire insect attaining a defence position. This posture is achieved by a specific cascade of movements: Head and legs interlock mutually and with specific features of thorax and the first abdominal ventrite, presumably to increase the mechanical stability of the beetle and to maintain the defence position with minimal muscle activity. The deterministic interaction of accurately fitting body parts follows a defined sequence, which resembles a piece of engineering.     

No evidence of sexual dimorphism in the tails of the swallowtail butterflies Papilio machaon gorganus and P. m. britannicus

The European swallowtail butterfly (Papilio machaon) is so named, because of the long and narrow prominences extending from the trailing edge of their hindwings and, although not a true tail, they are referred to as such. Despite being a defining feature, an unequivocal function for the tails is yet to be determined, with predator avoidance (diverting an attack from the rest of the body), and enhancement of aerodynamic performance suggested. The swallowtail, however, is sexually size dimorphic with females larger than males, but whether the tail is also sexually dimorphic is unknown. Here, museum specimens were used to determine whether sexual selection has played a role in the evolution of the swallowtail butterfly tails in a similar way to that seen in the tail streamers of the barn swallow (Hirundo rustica), where the males have longer streamers than those of the females. Previously identified sexual dimorphism in swallowtail butterfly size was replicated, but no evidence for dimorphism in tail length was found. If evolved to mimic antennae and a head to divert a predatory attack, and if an absolute tail size was the most effective for this, then the tail would probably be invariant with butterfly hindwing size. The slope of the relationship between tail length and size, however, although close to zero, was nonetheless statistically significantly above (tail length ∝ hindwing area ^{0.107 ± 0.011}). The slope also did not equate to that expected for geometric similarity (tail length ∝ hindwing area^1/2) suggesting that tail morphology is not solely driven by aerodynamics. It seems likely then, that tail morphology is primarily determined by, and perhaps a compromise of several, factors associated with predator avoidance (e.g. false head mimicry and a startling function). Of course, experimental data are required to confirm this.     

Three‐dimensional geometry of a pterosaur wing skeleton,and its implications for aerial and terrestrial locomotion

This study reports on the three‐dimensional spatial arrangement and movements of the skeleton of Anhanguera santanae (Pterodactyloidea: Ornithocheiridae), determined using exceptionally well‐preserved uncrushed fossil material, and a rigid‐body method for analysing the joints of extinct animals. The geometric results of this analysis suggest that the ornithocheirids were inherently unstable in pitch and yaw. As a result, pitch control would probably have been brought about by direct adjustment of the angle of attack of the wing, by raising or lowering the trailing edge from the root using the legs if, as is indicated in soft‐tissue specimens of a number of unrelated pterosaur species, the legs were attached to the main wing membrane, or by using long‐axis rotations at the shoulder or wrist to raise and lower the trailing edge from the wingtip. An analysis of the three‐dimensional morphology of the wrist lends support to the idea that the pteroid – a long, slender wrist bone unique to pterosaurs that supported a membranous forewing – was directed forwards in flight, not towards the body. As a result, the forewing could have fulfilled the function of an air‐brake and high‐lift device, and may also have had an important role in pitch, yaw, and roll control. The joint analysis is consistent with a semi‐erect quadrupedal model of terrestrial locomotion in the ornithocheirids. © 2008 The Linnean Society of London, Zoological Journal of the Linnean Society, 2008, 154 , 27–69.     

Systematic implications of the Psilotaceae

To assess the taxonomic relationships between the Psilotaceae and the Filicales ( = Polypodiales), certain factors including character divergence, gaps in the record, categorical consistency, conservatism of characters, and use of factual vs. hypothetical data have been given consideration. Although it has been proposed that the aerial shoots of Psilotaceae are homologous to fronds, and the appendages to pinnae, and that the Psilotaceae should be classified as Filicales,Psilotum andTmesipteris show a number of profound differences from Filicales. These involve the structure of the aerial organs, vascular patterns, fertile appendages, and sporangia. In view of the taxonomic criteria used, and the nature of the character differences, it is concluded that the Psilotaceae do not warrant inclusion in Filicales. InsteadPsilotum andTmesipteris constitute a separate line of evolution, and should be treated as a class, the Psilopsida, of Tracheophyta, equivalent to Equisetopsida, Lycopodiopsida, and Polypodiopsida.     

Captopodus poschmanni gen. et sp. nov. a new stem-group arthropod from the Lower Devonian Hunsrück Slate (Germany)

A new arthropod from the Lower Devonian Hunsrück Slate is described on the basis of four specimens. The body of Captopodus poschmanni comprises a head, a trunk with an anal portion. The high number of trunk appendages (≥66 segments) is unusual. The function of one pair of cupola-like structures of the head shield is unclear. The presence of large grasping appendages in the head superficially resembles the ‘short great appendages’ of other euarthropods and grasping appendages of thylacocephalans. The phylogenetic position of the arthropod cannot be determined in detail, though several morphological aspects indicate a phylogenetic position as a stem lineage representative of the Euarthropoda, the morphology of the trunk appendages seem to indicate a more advanced phylogenetic position. This new taxon underlines the exceptional diversity of arthropods within the Hunsrück Slate in comparison to other Devonian fossil sites and highlights the significance of the Hunsrück Slate for the evolution of early arthropods.     

Toward Fast and Efficient Mobility in Aquatic Environment: A Robot with Compliant Swimming Appendages Inspired by a Water Beetle

Water beetles are proficient drag-powered swimmers,with oar-like legs.Inspired by this mechamsm,here we propose a miniature robot,with mobility provided by a pair of legs with swimming appendages.The robot has optimized linkage structure to maximize the stroke angle,which is actuated by a single DC motor with a series of gears and a spring.A simplified swimming appendage model is proposed to calculate the deflection due to the applied drag force,and is compared with simulated data using COMSOL Multiphysics.Also,the swimming appendages are optimized by considering their locations on the legs using two fitness functions,and six different configurations are selected.We investigate the performance of the robot with various types of appendage using a high-speed camera,and motion capture cameras.The robot with the proposed configuration exhibits fast and efficient movement compared with other robots.In addition,the locomotion of the robot is analyzed by considering its dynamics,and compared with that of a water boatman (Corixidae).     

Hopping and climbing gait of Japanese Pygmy Woodpeckers (Picoides kizuki)

Single cycles of hopping and climbing were investigated in Japanese Pygmy Woodpeckers Picoides kizuki using motion analyses on video. Body movements on substrate angled from 0–90° were compared for every 10°. The body was inclined forward during stance phase for both small and large substrate angles, and the inclination amplitude increased when the substrate angle increased. The tail was bent ventrally almost simultaneously to this body inclination, and its amplitude was apparently high at large substrate angles. Most of the gait parameters changed when the stride length increased. The minimum body–tail angle and most of the parameters representing body movements during stance phase changed when the substrate angle increased, probably because gravity pulled the birds further backward when they were moving on a steeper slope. These parameters showed a clear difference between the data on substrate steeper than 40° and lower than 30°. The abrupt changes in these parameters most likely mean that the motor pattern changed from hopping to climbing between these angles.     

The soft anatomy of Isoxys minor from the Guanshan fauna,lower Cambrian of Southwest China

Isoxys is a very common Cambrian bivalved arthropod, specimens of which are normally preserved only as valves. The discovery of the soft anatomy of Isoxys may greatly assist understanding affinities and functional morphology. Isoxys minor Luo and Hu in Luo et al., 2008 is the most common representative of all animal species known from the lower Cambrian Guanshan fauna (Cambrian Series 2, Stage 4) at the Shitangshan Section, near Kunming, Yunnan Province, Southwest China. Here we describe and reconstruct the morphology of I. minor on the basis of newly illustrated fossils and a few new specimens that bear soft-parts including new discovery of frontal grasping appendages. Like the soft anatomy of other known Isoxys, it bears a pair of large stalked eyes, a pair of specialized frontal grasping appendages, approximately 12–14 paired biramous limbs, and a helm-like tail exposed outside the valves.     

Maintenance of Human Vertical Posture upon Asymmetric Leg Loading and Fixation of the Knee Joint of One Leg

Maintenance of a vertical posture was studied in standing subjects with a fixed knee joint of one leg and a different weight distribution between the legs. Knee fixation on one leg did not affect the speed of movements of the common center of pressure (CP) at any weight distribution between the legs, and the stability of vertical posture was therefore unchanged. However, the relative contributions of the legs to the posture control changed when knee movements of one leg were restricted. The speed of CP movements of the free leg was independent of the weight loading on the leg. The speed of CP movements of the leg with the knee fixed depended on the weight distribution and was higher when the leg was loaded. Thus, the leg with the fixed knee joint made a greater contribution to maintaining vertical posture when the leg was loaded. Yet its contribution was comparable with that of the unloaded free contralateral leg even in this case, as was evident from lack of differences in CP movements between the two legs. It was assumed that the leg with the free knee joint played a major role in maintaining equilibrium of vertical posture, while the leg with the fixed knee joint mostly acted to more finely adjust the body position.     

Patterns of turning in courtship orientation of the male German cockroach

Courtship turning of the male German cockroach, Blattella germanica, was analysed with respect to rotational and translational movements. Three different sources of orientation information are postulated for the control of this behaviour: external sensory information (perception of sex pheromone) releases courtship, proprioception from the legs is required to curtail turning when the specified turn angle is reached, and internally stored information determines the sign of turning and patterns the courtship actions.     

An evolutionary treatment of the morphology and physiology of circulatory organs in insects

An overview from an evolutionary perspective is presented on the research of the past 2 decades on insect circulatory organs. Based on various functional morphology it is clear that the flow mode of the dorsal vessel ('heart') has changed during the evolution of hexapods. In all apterygotes and mayflies the flow is bidirectional. In most pterygote insects, however, it is unidirectional. In some endopterygote insects, the direction of the flow alternates. This is achieved by heartbeat reversal, which may have various physiological functions and is a derived condition that probably occurred several times during the course of insect evolution. Special attention is given to the hemolymph flow in body appendages. In ancestral hexapods, they are supplied by arteries, whereas circulation in appendages of higher insects is accomplished by accessory pulsatile organs. These auxiliary hearts are autonomous pumps and exhibit a great diversity in their functional morphology. They represent evolutionary innovations which evolved by recruitment of building blocks from various organ systems and were assembled into new functional units. Almost all pulsatile circulatory organs in insects investigated exhibit a myogenic automatism with a superimposed neuronal control. The neuroanatomy of insect circulatory organs has been investigated only in a small number of species but in considerable detail. Numerous potential peptidergic and a few aminergic mediators could be demonstrated by immunocytochemical and biochemical methods. The cardiotropic effectiveness of these mediators may vary among species and it can be stated that there is no uniform picture of the control of the various circulatory organs in insects. A possible explanation for the differences may lie in the different evolutionary origins of the muscular components. Furthermore, insect circulatory organs may represent important neurohemal releasing sites.     

Non-Jumping Take off Performance in Beetle Flight （Rhinoceros Beetle Trypoxylus dichotomus）

In recent decades, the take-off mechanisms of flying animals have received much attention in insect flight initiation. Most of previous works have focused on the jumping mechanism, which is the most common take-off mechanism found in flying animals. Here, we presented that the rhinoceros beetle, Trypoxylus dichotomus, takes offwithout jumping. In this study, we used 3-Dimensional （3D） high-speed video techniques to quantitatively analyze the wings and body kinematics during the initiation periods of flight. The details of the flapping angle, angle of attack of the wings and the roll, pitch and yaw angles of the body were investigated to understand the mechanism of take-off in T. dichotomus. The beetle took off gradually with a small velocity and small acceleration. The body kinematic analyses showed that the beetle exhibited stable take-off. To generate high lift force, the beetle modulated its hind wing to control the angle of attack; the angle of attack was large during the upstroke and small during the downstroke. The legs of beetle did not contract and strongly release like other insects. The hind wing could be con- sidered as a main source of lift for heavy beetle.     

Two new marine pleurostomatid ciliates from China,Amphileptus gui nov. spec. and Amphileptus yuianus nov. spec. (Ciliophora,Pleurostomatida)

The morphology and infraciliature of two pleurostomatid ciliates, Amphileptus gui nov. spec. and A. yuianus nov. spec., collected from mariculture ponds near Qingdao (Tsingtao), China, were investigated using living observations and the protargol impregnation method. These new species are distinguished from their congeners by a combination of characters including their marine habitat and the presence of an apical group of densely packed extrusomes. Amphileptus gui nov. spec. differs from A. yuianus nov. spec. mainly in the number of contractile vacuoles (3–7 vs. 1), the shape of extrusomes (thin bar-like vs. clavate), and the number of left and right somatic kineties (7–11 and 37–50 vs. 4 and 18–22).     

The avian tail reduces body parasite drag by controlling flow separation and vortex shedding.

The aerodynamic effect of the furled avian tail on the parasite drag of a bird's body was investigated on mounted, frozen European starling Sturnus vulgaris in a wind tunnel at flight speeds between 6 and 14 m s(-1). Removal of tail rectrices and dorsal and ventral covert feathers at the base of the tail increased the total parasite drag of the body and tail by between 25 and 55%. Flow visualization and measurements of dynamic pressure in the tail boundary layer showed that in the intact bird a separation bubble forms on the ventral side of the body, and reattaches to the ventral side of the tail. This bubble is a consequence of the morphology of the body, with a rapid contraction posterior to the pelvis and hind legs. The tail and the covert feathers at its base act as a combined splitter plate and wedge to control vortex shedding and body wake development, and thereby are important to minimize drag. This hitherto unsuspected mechanism is central to understanding the morphology of the avian body, and may have had a significant influence on the evolution of avian tail morphology by pre-adapting the tail for radiation and specialization as an aerodynamic lifting structure and as an organ of communication in sexual selection.