Animal aloft: the origins of aerial behavior and flight

The transition to flying insects: lessons from evo-devo and fossils

Insects are the only arthropod group to achieve powered flight, which facilitated their explosive radiation on land. It remains a significant challenge to understand the evolutionary transition from nonflying (apterygote) to flying (pterygote) insects due to the large gap in the fossil record. Under such a situation, ontogenic information has historically been used to compensate for fossil evidence. Recent evo-devo studies support and refine a paleontology-based classical hypothesis that an ancestral exite incorporated into the body wall contributed to the origin of insect wings. The modern hypothesis locates an ancestral precoxa leg segment with an exite within the hexapod lateral tergum, reframing the long-standing debate on the insect wing origin. A current focus is on the contributions of the incorporated exite homolog and surrounding tissues, such as the pleuron and the medial bona fide tergum, to wing evolution. In parallel, recent analyses of Paleozoic fossils have confirmed thoracic and abdominal lateral body outgrowths as transitional wing precursors and suggested their possible role as respiratory organs in aquatic or semiaquatic environments. These recent studies have revised our understanding of the transition to flying insects. This review highlights recent progress in both evo-devo and paleontology, and discusses future challenges, including the evolution of metamorphic development.

Vascular and Osteological Morphology of Expanded Digit Tips Suggests Specialization in the Wandering Salamander (Aneides vagrans)

For over a century researchers have marveled at the square-shaped toe tips of several species of climbing salamanders (genus Aneides), speculating about the function of large blood sinuses therein. Wandering salamanders (Aneides vagrans) have been reported to exhibit exquisite locomotor control while climbing, jumping, and gliding high (88 m) within the redwood canopy; however, a detailed investigation of their digital vascular system has yet to be conducted. Here, we describe the vascular and osteological structure of, and blood circulation through, the distal regions of the toes of A. vagrans using histology in tandem with live-animal videos. Specifically, we sectioned a toe of A. vagrans at 0.90 μm, embedded it in Spurrs resin, and stained the tissue with toluidine blue. An additional three toes were sectioned at 10 μm, embedded in paraffin, and after sectioning and mounting, treated with Verhoeff and Quad stains. For living salamanders, we recorded real-time videos of blood flowing within individual toes upon a translucent surface oriented both horizontally (0°) and vertically (90°) to simulate both prostrate and vertical clinging scenarios, then analyzed the image sequences using ImageJ. We found that the vascularized toe tips have one large sinus cavity that is divided more proximally into two chambers via a septum, and there are mucous and granular glands in the dorsal and dorsolateral integument of the digit tips. Live-animal trials revealed variable sinus-filling both within and between toes, seemingly associated with variable pressure applied to the substrate when standing, stepping, clinging, and climbing. We conclude that A. vagrans, and likely other climbing salamanders, can functionally fill, trap, and drain the blood in their vascularized toe tips to optimize attachment, detachment, and complex arboreal locomotion (e.g., landing after gliding flight). Such an adaptation could provide insights for bioinspired designs.

Biomechanics and ontogeny of gliding in wingless stick insect nymphs (Extatosoma tiaratum)

Many wingless arboreal arthropods can glide back to tree trunks following free falls. However, little is known about the behaviors and aerodynamics underlying such aerial performance, and how this may be influenced by body size. Here, we studied gliding performance by nymphs of the stick insect Extatosoma tiaratum, focusing on the dynamics of J-shaped trajectories and how gliding capability changes during ontogeny. After being dropped 40 cm horizontally from a visual target, the first-instar nymphs landed on the target within 1.1 s. After reaching terminal speed (at ∼0.25 s), they initiated gliding with significant horizontal force, during which the overall lift-to-drag ratio increased from 0.16 to 0.48. This transition from parachuting to gliding is characterized by a damped oscillation in body pitch, initiated with a rapid nose-down pitching, and led to a higher-lift configuration with reduced body angle of attack. Among instars, increasing wing loading during ontogeny led to greater terminal speed, reduced agility during glide initiation and increased glide angle. Our study demonstrates that a sequence of controlled behaviors, from pre-glide descent to glide initiation and forward gliding, underlies their gliding aerodynamics, which in aggregate form the basis for J-shaped aerial trajectories. Selection for improved gliding performance in wingless arthropods may foster the evolution of more rapid maneuvers and of dedicated morphological traits (such as winglets) that contribute to an overall reduction in wing loading, either across ontogeny or during the evolution of larger body size.

Insect Flight: State of the Field and Future Directions

The evolution of flight in an early winged insect ancestral lineage is recognized as a key adaptation explaining the unparalleled success and diversification of insects. Subsequent transitions and modifications to flight machinery, including secondary reductions and losses, also play a central role in shaping the impacts of insects on broadscale geographic and ecological processes and patterns in the present and future. Given the importance of insect flight, there has been a centuries-long history of research and debate on the evolutionary origins and biological mechanisms of flight. Here, we revisit this history from an interdisciplinary perspective, discussing recent discoveries regarding the developmental origins, physiology, biomechanics, and neurobiology and sensory control of flight in a diverse set of insect models. We also identify major outstanding questions yet to be addressed and provide recommendations for overcoming current methodological challenges faced when studying insect flight, which will allow the field to continue to move forward in new and exciting directions. By integrating mechanistic work into ecological and evolutionary contexts, we hope that this synthesis promotes and stimulates new interdisciplinary research efforts necessary to close the many existing gaps about the causes and consequences of insect flight evolution.

Wax "tails" enable planthopper nymphs to self-right midair and land on their feet

The striking appearance of wax 'tails' - posterior wax projections on planthopper nymphs - has captivated entomologists and naturalists alike. Despite their intriguing presence, the functional roles of these structures remain largely unexplored. This study leverages high-speed imaging to uncover the biomechanical implications of these wax formations in the aerial dynamics of planthopper nymphs (Ricania sp.). We quantitatively demonstrate that removing wax tails significantly increases body rotations during jumps. Specifically, nymphs without wax projections undergo continuous rotations, averaging 4.3 ± 1.9 per jump, in contrast to wax-intact nymphs, who narrowly complete a full rotation, averaging only 0.7 ± 0.2 per jump. This suggests that wax structures effectively counteract rotation through aerodynamic drag forces. These stark differences in body rotation correlate with landing success: nymphs with wax intact achieve a near perfect landing rate of 98.5%, while those without wax manage only a 35.5% success rate. Jump trajectory analysis reveals transitions from parabolic to Tartaglia shapes at higher take-off velocities for wax-intact nymphs, illustrating how wax structures assist nymphs in achieving stable, controlled descents. Our findings confirm the aerodynamic self-righting functionality of wax tails in stabilizing planthopper landings, advancing our understanding of the complex interplay between wax morphology and aerial maneuverability, with broader implications for the evolution of flight in wingless insects and bioinspired robotics.

Mosquitoes escape looming threats by actively flying with the bow wave induced by the attacker

To detect and escape looming threats, night-flying insects must rely on other senses than vision alone. Nocturnal mosquitoes can evade looming objects in the dark, but how they achieve this is still unknown. Here, we show how night-active female malaria mosquitoes escape from rapidly looming objects that simulate defensive actions of blood-hosts. First, we quantified the escape performance of flying mosquitoes from an event-triggered mechanical swatter, showing that mosquitoes use swatter-induced airflow to increase their escape success. Secondly, we used high-speed videography and deep-learning-based tracking to analyze escape flights in detail, showing that mosquitoes use banked turns to evade the threat. By combining escape kinematics data with numerical simulations of attacker-induced airflow and a mechanistic movement model, we unraveled how mosquitoes control these banked evasive maneuvers: they actively steer away from the danger, and then passively travel with the bow wave produced by the attacker. Our results demonstrate that night-flying mosquitoes can detect looming objects when visual cues are minimal, suggesting that they use attacker-induced airflow both to detect the danger and as a fluid medium to move with away from the threat. This shows that escape strategies of flying insects are more complex than previous visually induced escape flight studies suggest. As most insects are of similar or smaller sizes than mosquitoes, comparable escape strategies are expected among millions of flying insect species. The here-observed escape maneuvers are distinct from those of mosquitoes escaping from odor-baited traps, thus providing new insights for the development of novel trapping techniques for integrative vector management.

Petal-shaped femoral lobes facilitate gliding in orchid mantises

To glide in forest canopies, arboreal vertebrates evolved various skin-derived aerodynamic structures, such as patagial membranes or webbing, but no comparable structure has been reported from wingless arboreal arthropods.1,2,3 Orchid mantises (Hymenopus coronatus) have been traditionally considered a textbook example of flower mimicry for ∼200 years due to their highly expanded, petal-shaped femoral lobes. However, the empirical evidence substantiating the petal-mimicry function of the femoral lobes has not been entirely conclusive.4,5,6 Observational and experimental evidence suggests that these lobes do not contribute to flower mimicry for luring pollinators6,7 and likely serve other functions.7,8 After observing their aerial escape initiated with active jumping, we hypothesized that orchid mantises can glide and that their femoral lobes are used for gliding. Through behavioral investigations and morphological analyses, we show that orchid mantis nymphs are excellent gliders, exhibiting the shallowest gliding trajectories observed in terrestrial invertebrates.9,10,11,12,13 The lobe extensions on their femoral segments are cambered airfoils, which increase the mantis projected area by ∼36% and play a vital role in the aerodynamic underpinning of the observed gliding. Despite a 165-fold increase in body mass throughout ontogeny, older female mantis nymphs maintained a persistent gliding capability. We further showed a notable 40%-56% reduction in wing loading attributed to the positive size allometry of these lobes, indicating a clear promotion of gliding throughout ontogeny. This is the first documentation of gliding-adapted "leg wings" in a wingless arthropod. The evolution of such structures is potentially common among arboreal arthropods and demands a systematic re-examination.

Air-to-land transitions: from wingless animals and plant seeds to shuttlecocks and bio-inspired robots

Recent observations of wingless animals, including jumping nematodes, springtails, insects, and wingless vertebrates like geckos, snakes, and salamanders, have shown that their adaptations and body morphing are essential for rapid self-righting and controlled landing. These skills can reduce the risk of physical damage during collision, minimize recoil during landing, and allow for a quick escape response to minimize predation risk. The size, mass distribution, and speed of an animal determine its self-righting method, with larger animals depending on the conservation of angular momentum and smaller animals primarily using aerodynamic forces. Many animals falling through the air, from nematodes to salamanders, adopt a skydiving posture while descending. Similarly, plant seeds such as dandelions and samaras are able to turn upright in mid-air using aerodynamic forces and produce high decelerations. These aerial capabilities allow for a wide dispersal range, low-impact collisions, and effective landing and settling. Recently, small robots that can right themselves for controlled landings have been designed based on principles of aerial maneuvering in animals. Further research into the effects of unsteady flows on self-righting and landing in small arthropods, particularly those exhibiting explosive catapulting, could reveal how morphological features, flow dynamics, and physical mechanisms contribute to effective mid-air control. More broadly, studying apterygote (wingless insects) landing could also provide insight into the origin of insect flight. These research efforts have the potential to lead to the bio-inspired design of aerial micro-vehicles, sports projectiles, parachutes, and impulsive robots that can land upright in unsteady flow conditions.

Ecological patterns and processes in the vertical dimension of terrestrial ecosystems

Climatic gradients such as latitude and elevation are considered primary drivers of global biogeography. Yet, alongside these macro-gradients, the vertical space and structure generated by terrestrial plants form comparable climatic gradients but at a fraction of the distance. These vertical gradients provide a spectrum of ecological space for species to occur and coexist, increasing biodiversity. Furthermore, vertical gradients can serve as pathways for evolutionary adaptation of species traits, leading to a range of ecological specialisations. In this review, we explore the ecological evidence supporting the proposition that the vertical gradient serves as an engine driving the ecology and evolution of species and shaping larger biogeographical patterns in space and time akin to elevation and latitude. Focusing on vertebrate and invertebrate taxa, we synthesised how ecological patterns within the vertical dimension shape species composition, distribution and biotic interactions. We identify three key ecological mechanisms associated with species traits that facilitate persistence within the vertical environment and draw on empirical examples from the literature to explore these processes. Looking forward, we propose that the vertical dimension provides an excellent study template to explore timely ecological and evolutionary questions. We encourage future research to also consider how the vertical dimension will influence the resilience and response of animal taxa to global change.

Anatomy and relationships of the early diverging Crocodylomorphs Junggarsuchus sloani and Dibothrosuchus elaphros

The holotype of Junggarsuchus sloani, from the Shishugou Formation (early Late Jurassic) of Xinjiang, China, consists of a nearly complete skull and the anterior half of an articulated skeleton, including the pectoral girdles, nearly complete forelimbs, vertebral column, and ribs. Here, we describe its anatomy and compare it to other early diverging crocodylomorphs, based in part on CT scans of its skull and that of Dibothrosuchus elaphros from the Early Jurassic of China. Junggarsuchus shares many features with a cursorial assemblage of crocodylomorphs, informally known as "sphenosuchians," whose relationships are poorly understood. However, it also displays several derived crocodyliform features that are not found among most "sphenosuchians." Our phylogenetic analysis corroborates the hypothesis that Junggarsuchus is closer to Crocodyliformes, including living crocodylians, than are Dibothrosuchus and Sphenosuchus, but not as close to crocodyliforms as Almadasuchus and Macelognathus, and that the "Sphenosuchia" are a paraphyletic assemblage. D. elaphros and Sphenosuchus acutus are hypothesized to be more closely related to Crocodyliformes than are the remaining non-crocodyliform crocodylomorphs, which form several smaller groups but are largely unresolved.

Gliding and parachuting by arboreal salamanders

Wandering salamanders (Aneides vagrans) reside in the crowns of the world's tallest trees and have been observed to readily jump from the canopy when disturbed^1,2. Here, we describe the aerial performance of falling A. vagrans, which maintain stable gliding postures via adjustments of the limbs and tail in lieu of specialized control surfaces. In wind tunnel trials, A. vagrans parachuted consistently and slowed their vertical speed by up to 10% while falling. Furthermore, A. vagrans coupled parachuting with parasagittal undulations of the tail and torso to effect gliding at non-vertical angles (minimum of ∼84°) in 58% of trials. Selection pressures imposed on falling from heights can be substantial, and have resulted in the evolution of diverse aerial behaviors among arboreal taxa; nonetheless, aerial behavior occurring in arboreal salamanders is surprising, and calls for further work on the natural occurrence of falling, gliding, and directed aerial descent in canopy-dwelling tetrapods.

Recovery mechanisms in the dragonfly righting reflex

Insects have evolved sophisticated reflexes to right themselves in mid-air. Their recovery mechanisms involve complex interactions among the physical senses, muscles, body, and wings, and they must obey the laws of flight. We sought to understand the key mechanisms involved in dragonfly righting reflexes and to develop physics-based models for understanding the control strategies of flight maneuvers. Using kinematic analyses, physical modeling, and three-dimensional flight simulations, we found that a dragonfly uses left-right wing pitch asymmetry to roll its body 180 degrees to recover from falling upside down in ~200 milliseconds. Experiments of dragonflies with blocked vision further revealed that this rolling maneuver is initiated by their ocelli and compound eyes. These results suggest a pathway from the dragonfly's visual system to the muscles regulating wing pitch that underly the recovery. The methods developed here offer quantitative tools for inferring insects' internal actions from their acrobatics, and are applicable to a broad class of natural and robotic flying systems.

Digital restoration of the pectoral girdles of two Early Cretaceous birds, and implications for early flight evolution

The morphology of the pectoral girdle, the skeletal structure connecting the wing to the body, is a key determinant of flight capability, but in some respects is poorly known among stem birds. Here, the pectoral girdles of the Early Cretaceous birds Sapeornis and Piscivorenantiornis are reconstructed for the first time based on computed tomography and three-dimensional visualization, revealing key morphological details that are important for our understanding of early-flight evolution. Sapeornis exhibits a double articulation system (widely present in non-enantiornithine pennaraptoran theropods including crown birds), which involves, alongside the main scapula-coracoid joint, a small subsidiary joint, though variation exists with respect to the shape and size of the main and subsidiary articular contacts in non-enantiornithine pennaraptorans. This double articulation system contrasts with Piscivorenantiornis in which a spatially restricted scapula-coracoid joint is formed by a single set of opposing articular surfaces, a feature also present in other members of Enantiornithines, a major clade of stem birds known only from the Cretaceous. The unique single articulation system may reflect correspondingly unique flight behavior in enantiornithine birds, but this hypothesis requires further investigation from a functional perspective. Our renderings indicate that both Sapeornis and Piscivorenantiornis had a partially closed triosseal canal (a passage for muscle tendon that plays a key role in raising the wing), and our study suggests that this type of triosseal canal occurred in all known non-euornithine birds except Archaeopteryx, representing a transitional stage in flight apparatus evolution before the appearance of a fully closed bony triosseal canal as in modern birds. Our study reveals additional lineage-specific variations in pectoral girdle anatomy, as well as significant modification of the pectoral girdle along the line to crown birds. These modifications produced diverse pectoral girdle morphologies among Mesozoic birds, which allowed a commensurate range of capability levels and styles to emerge during the early evolution of flight.

A First Principles Approach to Subjective Experience

Understanding the neural bases of subjective experience remains one of the great challenges of the natural sciences. Higher-order theories of consciousness are typically defended by assessments of neural activity in higher cortical regions during perception, often with disregard to the nature of the neural computations that these regions execute. We have sought to refocus the problem toward identification of those neural computations that are necessary for subjective experience with the goal of defining the sorts of neural architectures that can perform these operations. This approach removes reliance on behaviour and brain homologies for appraising whether non-human animals have the potential to subjectively experience sensory stimuli. Using two basic principles—first, subjective experience is dependent on complex processing executing specific neural functions and second, the structure-determines-function principle—we have reasoned that subjective experience requires a neural architecture consisting of stacked forward models that predict the output of neural processing from inputs. Given that forward models are dependent on appropriately connected processing modules that generate prediction, error detection and feedback control, we define a minimal neural architecture that is necessary (but not sufficient) for subjective experience. We refer to this framework as the hierarchical forward models algorithm. Accordingly, we postulate that any animal lacking this neural architecture will be incapable of subjective experience.

Tails stabilize landing of gliding geckos crashing head-first into tree trunks

Animals use diverse solutions to land on vertical surfaces. Here we show the unique landing of the gliding gecko, Hemidactylus platyurus. Our high-speed video footage in the Southeast Asian rainforest capturing the first recorded, subcritical, short-range glides revealed that geckos did not markedly decrease velocity prior to impact. Unlike specialized gliders, geckos crashed head-first with the tree trunk at 6.0 ± 0.9 m/s (~140 body lengths per second) followed by an enormous pitchback of their head and torso 103 ± 34° away from the tree trunk anchored by only their hind limbs and tail. A dynamic mathematical model pointed to the utility of tails for the fall arresting response (FAR) upon landing. We tested predictions by measuring foot forces during landing of a soft, robotic physical model with an active tail reflex triggered by forefoot contact. As in wild animals, greater landing success was found for tailed robots. Experiments showed that longer tails with an active tail reflex resulted in the lower adhesive foot forces necessary for stabilizing successful landings, with a tail shortened to 25% requiring over twice the adhesive foot force.

Mechanisms for mid-air reorientation using tail rotation in gliding geckos

Arboreal animals face numerous challenges when negotiating complex three-dimensional terrain. Directed aerial descent or gliding flight allows for rapid traversal of arboreal environments, but presents control challenges. Some animals, such as birds or gliding squirrels, have specialized structures to modulate aerodynamic forces while airborne. However, many arboreal animals do not possess these specializations but still control posture and orientation in mid-air. One of the largest inertial segments in lizards is their tail. Inertial reorientation can be used to attain postures appropriate for controlled aerial descent. Here, we discuss the role of tail inertia in a range of mid-air reorientation behaviors using experimental data from geckos in combination with mathematical and robotic models. Geckos can self-right in mid-air by tail rotation alone. Equilibrium glide behavior of geckos in a vertical wind tunnel show that they can steer toward a visual stimulus by using rapid, circular tail rotations to control pitch and yaw. Multiple coordinated tail responses appear to be required for the most effective terminal velocity gliding. A mathematical model allows us to explore the relationship between morphology and the capacity for inertial reorientation by conducting sensitivity analyses, and testing control approaches. Robotic models further define the limits of performance and generate new control hypotheses. Such comparative analysis allows predictions about the diversity of performance across lizard morphologies, relative limb proportions, and provides insights into the evolution of aerial behaviors.

Canopy parkour: movement ecology of post-hatch dispersal in a gliding nymphal stick insect, Extatosoma tiaratum

For flightless arboreal arthropods, moving from the understory into tree canopies is cognitively and energetically challenging because vegetational structures present complex three-dimensional landscapes with substantial gaps. Predation risk and wind-induced perturbations in the canopy may further impede the movement process. In the Australian stick insect Extatosoma tiaratum, first-instar nymphs hatch on the forest floor and disperse toward tree canopies in the daytime. Here, we addressed how their tactic responses to environmental cues and movement strategies are adapted to the canopy environment. Newly hatched nymphs ascend with high endurance, travelling >100 m within 60 min. Navigation toward open canopies is underpinned by negative gravitaxis, positive phototaxis and visual responses to vertically oriented contrast patterns. Nymphal E. tiaratum also use directed jumping to cross gaps, and respond to tactile stimulation and potential threat with a self-dropping reflex, resulting in aerial descent. Post-hatch dispersal in E. tiaratum thus consists of visually mediated displacement both on vegetational structures and in the air; within the latter context, gliding is then an effective mechanism enabling recovery after predator- and perturbation-induced descent. These results further support the importance of a diurnal niche, in addition to the arboreal spatial niche, in the evolution of gliding in wingless arboreal invertebrates.

The craniomandibular anatomy of the early archosauriform Euparkeria capensis and the dawn of the archosaur skull

Archosauria (birds, crocodilians and their extinct relatives) form a major part of terrestrial ecosystems today, with over 10 000 living species, and came to dominate the land for most of the Mesozoic (over 150 Myr) after radiating following the Permian-Triassic extinction. The archosaur skull has been essential to this diversification, itself diversified into myriad forms. The archosauriform Euparkeria capensis from the Middle Triassic (Anisian) of South Africa has been of great interest since its initial description in 1913, because its anatomy shed light on the origins and early evolution of crown Archosauria and potentially approached that of the archosaur common ancestor. Euparkeria has been widely used as an outgroup in phylogenetic analyses and when investigating patterns of trait evolution among archosaurs. Although described monographically in 1965, subsequent years have seen great advances in the understanding of early archosaurs and in imaging techniques. Here, the cranium and mandible of Euparkeria are fully redescribed and documented using all fossil material and computed tomographic data. Details previously unclear are fully described, including vomerine dentition, the epiptergoid, number of premaxillary teeth and palatal arrangement. A new diagnosis and cranial and braincase reconstruction is provided, and an anatomical network analysis is performed on the skull of Euparkeria and compared with other amniotes. The modular composition of the cranium suggests a flexible skull well adapted to feeding on agile food, but with a clear tendency towards more carnivorous behaviour, placing the taxon at the interface between ancestral diapsid and crown archosaur ecomorphology, corresponding to increases in brain size, visual sensitivity, upright locomotion and metabolism around this point in archosauriform evolution. The skull of Euparkeria epitomizes a major evolutionary transition, and places crown archosaur morphology in an evolutionary context.

Evolution of fossorial locomotion in the transition from tetrapod to snake-like in lizards

Dramatic evolutionary transitions in morphology are often assumed to be adaptive in a new habitat. However, these assumptions are rarely tested because such tests require intermediate forms, which are often extinct. In vertebrates, the evolution of an elongate, limbless body is generally hypothesized to facilitate locomotion in fossorial and/or cluttered habitats. However, these hypotheses remain untested because few studies examine the locomotion of species ranging in body form from tetrapod to snake-like. Here, we address these functional hypotheses by testing whether trade-offs exist between locomotion in surface, fossorial and cluttered habitats in Australian Lerista lizards, which include multiple intermediate forms. We found that snake-like species penetrated sand substrates faster than more lizard-like species, representing the first direct support of the adaptation to fossoriality hypothesis. By contrast, body form did not affect surface locomotion or locomotion through cluttered leaf litter. Furthermore, all species with hindlimbs used them during both fossorial and surface locomotion. We found no evidence of a trade-off between fossorial and surface locomotion. This may be either because Lerista employed kinematic strategies that took advantage of both axial- and limb-based propulsion. This may have led to the differential occupation of their habitat, facilitating diversification of intermediate forms.

The braincase of Mesosuchus browni (Reptilia, Archosauromorpha) with information on the inner ear and description of a pneumatic sinus

Rhynchosauria is a group of archosauromorph reptiles abundant in terrestrial ecosystems of the Middle Triassic. Mesosuchus is one of the earliest and basalmost rhynchosaurs, playing an important role not only for the understanding of the evolution of the group as a whole, but also of archosauromorphs in general. The braincase of Mesosuchus has been previously described, albeit not in detail, and the middle and inner ears were missing. Here, we provide new information based on micro-computed tomography scanning of the best-preserved specimen of Mesosuchus, SAM-PK-6536. Contrary to what has been stated previously, the braincase of Mesosuchus is dorso-ventrally tall. The trigeminal foramen lies in a deep recess on the prootic whose flat ventral rim could indicate the articulation surface to the laterosphenoid, although no such element was found. The middle ear of Mesosuchus shows a small and deeply recessed fenestra ovalis, with the right stapes preserved in situ. It has a rather stout, imperforated and posteriorly directed shaft with a small footplate. These features suggest that the ear of Mesosuchus was well-suited for the detection of low-frequency sounds. The semicircular canals are slender and elongate and the floccular fossa is well-developed. This is indicative of a refined mechanism for gaze stabilization, which is usually related to non-sprawling postures. The most striking feature of the Mesosuchus braincase is, however, the presence of a pneumatic sinus in the basal tubera. The sinus is identified as originating from the pharyngotympanic system, implying ossified Eustachian tubes. Braincase pneumatization has not yet been a recognized feature of stem-archosaurs, but the potential presence of pneumatic foramina in an array of taxa, recognized here as such for the first time, suggests braincase sinuses could be present in many other archosauromorphs.

Dropping to escape: a review of an under-appreciated antipredator defence

Dropping is a common antipredator defence that enables rapid escape from a perceived threat. However, despite its immediate effectiveness in predator-prey encounters (and against other dangers such as a parasitoid or an aggressive conspecific), it remains an under-appreciated defence strategy in the scientific literature. Dropping has been recorded in a wide range of taxa, from primates to lizards, but has been studied most commonly in insects. Insects have been found to utilise dropping in response to both biotic and abiotic stimuli, sometimes dependent on mechanical or chemical cues. Whatever the trigger for dropping, the decision to drop by prey will present a range of inter-related costs and benefits to the individual and so there will be subtle complexities in the trade-offs surrounding this defensive behaviour. In predatory encounters, dropping by prey will also impose varying costs and benefits on the predator - or predators - involved in the system. There may be important trade-offs involved in the decision made by predators regarding whether to pursue prey or not, but the predator perspective on dropping has been less explored at present. Beyond its function as an escape tactic, dropping has also been suggested to be an important precursor to flight in insects and further study could greatly improve understanding of its evolutionary importance. Dropping in insects could also prove of significant practical importance if an improved understanding can be applied to integrated pest-management strategies. Currently the non-consumptive effects of predators on their prey are under-appreciated in biological control and it may be that the dropping behaviour of many pest species could be exploited via management practices to improve crop protection. Overall, this review aims to provide a comprehensive synthesis of the current literature on dropping and to raise awareness of this fascinating and widespread behaviour. It also seeks to offer some novel hypotheses and highlight key avenues for future research.

Jumping and the aerial behavior of aquatic mayfly larvae (Myobaetis ellenae, Baetidae)

Mayfly larvae generally are aquatic, but some madicolous taxa (i.e., living in thin water films) crawl over rocks within streams and waterfalls. When startled, these larvae can break the water film, jump, and enter an aerial phase of locomotion. Because mayfly larvae have been suggested as potential exemplars for the origin of insect wings as tracheal gills, and furthermore represent the most basal extant lineage of pterygotes, we analyzed jumping behavior and free-fall trajectories for one such species of mayfly (Myobaetis ellenae, Baetidae) in Costa Rica. Jumping was commonplace in this taxon, but was undirected and was characterized by body spinning at high angular velocities. No aerodynamic role for the tracheal gills was evident. By contrast, jumping by a sympatric species of bristletail (Meinertellus sp., Archaeognatha) consistently resulted in head-first and stable body postures during aerial translation. Although capable of intermittently jumping into the air, the mayfly larvae could neither control nor target their aerial behavior. By contrast, a stable body posture during jumps in adult bristletails, together with the demonstrated capacity for directed aerial descent in arboreal representatives of this order, support ancestrally terrestrial origins for insect flight within the behavioral context of either jumping or falling from heights.

A century and a half of research on the evolution of insect flight

The gill and paranotal lobe theories of insect wing evolution were both proposed in the 1870s. For most of the 20th century, the paranotal lobe theory was more widely accepted, probably due to the fundamentally terrestrial tracheal respiratory system; in the 1970s, some researchers advocated for an elaborated gill ("pleural appendage") theory. Lacking transition fossils, neither theory could be definitively rejected. Winged insects are abundant in the fossil record from the mid-Carboniferous, but insect fossils are vanishingly rare earlier, and all earlier fossils are from primitively wingless insects. The enigmatic, isolated mandibles of Rhyniognatha (early Devonian) hint that pterygotes may have been present much earlier, but the question remains open. In the late 20th century, researchers used models to study the interaction of body and protowing size on solar warming and gliding abilities, and stability and glide effectiveness of many tiny adjustable winglets versus a single, large pair of immobile winglets. Living stoneflies inspired the surface-skimming theory, which provides a mechanism to bridge between aquatic gills and flapping wings. The serendipitously discovered phenomenon of directed aerial descent suggests a likely route to the early origin of insect flight. It provides a biomechanically feasible sequence from guided falls to fully-powered flight.

Leaping lizards landing on leaves: escape-induced jumps in the rainforest canopy challenge the adhesive limits of geckos

The remarkable adhesive capabilities of geckos have garnered attention from scientists and the public for centuries. Geckos are known to have an adhesive load-bearing capacity far in excess (by 100-fold or more) of that required to support their body mass or accommodate the loading imparted during maximal locomotor acceleration. Few studies, however, have investigated the ecological contexts in which geckos use their adhesive system and how this may influence its properties. Here we develop a modelling framework to assess whether their prodigious adhesive capacity ever comes under selective challenge. Our investigation is based upon observations of escape-induced aerial descents of canopy-dwelling arboreal geckos that are rapidly arrested by clinging to leaf surfaces in mid-fall. We integrate ecological observations, adhesive force measurements, and body size and shape measurements of museum specimens to conduct simulations. Using predicted bending mechanics of petioles and leaf midribs, we find that the drag coefficient of the gecko, the size of the gecko and the size of the leaf determine impact forces. Regardless of the landing surface, safety factors for geckos range from a maximum of just over 10 to a minimum of well under one, which would be the point at which the adhesive system fails. In contrast to previous research that intimates that gecko frictional adhesive capacity is excessive relative to body mass, we demonstrate that realistic conditions in nature may result in frictional capacity being pushed to its limit. The rapid arrest of the lizard from its falling velocity likely results in the maximal loading to which the adhesive system is exposed during normal activities. We suggest that such activities might be primary determinants in driving their high frictional adhesive capacity.

Evolution of avian flight: muscles and constraints on performance

Competing hypotheses about evolutionary origins of flight are the 'fundamental wing-stroke' and 'directed aerial descent' hypotheses. Support for the fundamental wing-stroke hypothesis is that extant birds use flapping of their wings to climb even before they are able to fly; there are no reported examples of incrementally increasing use of wing movements in gliding transitioning to flapping. An open question is whether locomotor styles must evolve initially for efficiency or if they might instead arrive due to efficacy. The proximal muscles of the avian wing output work and power for flight, and new research is exploring functions of the distal muscles in relation to dynamic changes in wing shape. It will be useful to test the relative contributions of the muscles of the forearm compared with inertial and aerodynamic loading of the wing upon dynamic morphing. Body size has dramatic effects upon flight performance. New research has revealed that mass-specific muscle power declines with increasing body mass among species. This explains the constraints associated with being large. Hummingbirds are the only species that can sustain hovering. Their ability to generate force, work and power appears to be limited by time for activation and deactivation within their wingbeats of high frequency. Most small birds use flap-bounding flight, and this flight style may offer an energetic advantage over continuous flapping during fast flight or during flight into a headwind. The use of flap-bounding during slow flight remains enigmatic. Flap-bounding birds do not appear to be constrained to use their primary flight muscles in a fixed manner. To improve understanding of the functional significance of flap-bounding, the energetic costs and the relative use of alternative styles by a given species in nature merit study.This article is part of the themed issue 'Moving in a moving medium: new perspectives on flight'.

Surface tension dominates insect flight on fluid interfaces

Flight on the 2D air-water interface, with body weight supported by surface tension, is a unique locomotion strategy well adapted for the environmental niche on the surface of water. Although previously described in aquatic insects like stoneflies, the biomechanics of interfacial flight has never been analysed. Here, we report interfacial flight as an adapted behaviour in waterlily beetles (Galerucella nymphaeae) which are also dexterous airborne fliers. We present the first quantitative biomechanical model of interfacial flight in insects, uncovering an intricate interplay of capillary, aerodynamic and neuromuscular forces. We show that waterlily beetles use their tarsal claws to attach themselves to the interface, via a fluid contact line pinned at the claw. We investigate the kinematics of interfacial flight trajectories using high-speed imaging and construct a mathematical model describing the flight dynamics. Our results show that non-linear surface tension forces make interfacial flight energetically expensive compared with airborne flight at the relatively high speeds characteristic of waterlily beetles, and cause chaotic dynamics to arise naturally in these regimes. We identify the crucial roles of capillary-gravity wave drag and oscillatory surface tension forces which dominate interfacial flight, showing that the air-water interface presents a radically modified force landscape for flapping wing flight compared with air.

Biomechanics of aerial righting in wingless nymphal stick insects

Numerous wingless arthropods as well as diverse vertebrates are capable of mid-air righting. We studied the biomechanics of the aerial righting reflex in first-instar nymphs of the stick insect Extatosoma tiaratum. After being released upside-down, insects reoriented dorsoventrally and stabilized body posture via active modulation of limb positions and associated aerodynamic torques. We identified specific reflexes for bilaterally asymmetric leg displacements which elicit body rotation and subsequently stabilize mid-air posture. Coordinated appendicular movements thus improve torsional manoeuvrability in the absence of wings, as may have characterized the initial origins of controlled aerial behaviour in arthropods. Design of small aerial or multimodal robotic vehicles may similarly benefit from use of such strategies for flight control.

Arachnid aloft: directed aerial descent in neotropical canopy spiders

The behaviour of directed aerial descent has been described for numerous taxa of wingless hexapods as they fall from the tropical rainforest canopy, but is not known in other terrestrial arthropods. Here, we describe similar controlled aerial behaviours for large arboreal spiders in the genus Selenops (Selenopidae). We dropped 59 such spiders from either canopy platforms or tree crowns in Panama and Peru; the majority (93%) directed their aerial trajectories towards and then landed upon nearby tree trunks. Following initial dorsoventral righting when necessary, falling spiders oriented themselves and then translated head-first towards targets; directional changes were correlated with bilaterally asymmetric motions of the anterolaterally extended forelegs. Aerial performance (i.e. the glide index) decreased with increasing body mass and wing loading, but not with projected surface area of the spider. Along with the occurrence of directed aerial descent in ants, jumping bristletails, and other wingless hexapods, this discovery of targeted gliding in selenopid spiders further indicates strong selective pressures against uncontrolled falls into the understory for arboreal taxa.

Flapping wing aerodynamics: from insects to vertebrates

More than a million insects and approximately 11,000 vertebrates utilize flapping wings to fly. However, flapping flight has only been studied in a few of these species, so many challenges remain in understanding this form of locomotion. Five key aerodynamic mechanisms have been identified for insect flight. Among these is the leading edge vortex, which is a convergent solution to avoid stall for insects, bats and birds. The roles of the other mechanisms – added mass, clap and fling, rotational circulation and wing–wake interactions – have not yet been thoroughly studied in the context of vertebrate flight. Further challenges to understanding bat and bird flight are posed by the complex, dynamic wing morphologies of these species and the more turbulent airflow generated by their wings compared with that observed during insect flight. Nevertheless, three dimensionless numbers that combine key flow, morphological and kinematic parameters – the Reynolds number, Rossby number and advance ratio – govern flapping wing aerodynamics for both insects and vertebrates. These numbers can thus be used to organize an integrative framework for studying and comparing animal flapping flight. Here, we provide a roadmap for developing such a framework, highlighting the aerodynamic mechanisms that remain to be quantified and compared across species. Ultimately, incorporating complex flight maneuvers, environmental effects and developmental stages into this framework will also be essential to advancing our understanding of the biomechanics, movement ecology and evolution of animal flight.

The ocelli of Archaeognatha (Hexapoda): Functional morphology, pigment migration and chemical nature of the reflective tapetum

The ocelli of Archaeognatha, or jumping bristletails, differ from typical insect ocelli in shape and field of view. While the shape of the lateral ocelli is highly variable among species, most Machiloidea have sole shaped lateral ocelli beneath the compound eyes and a median ocellus that is oriented downward. This study investigated morphological and physiological aspects of the ocelli of Machilis hrabei and Lepismachilis spp.

The light reflecting ocellar tapetum in Machilis hrabei is made up by xanthine nanocrystals, as demonstrated by confocal Raman spectroscopy. Pigment granules in the photoreceptor cells move behind the tapetum in the dark adapted state. Such a vertical pigment migration in combination with a tapetum has not been described for any insect ocellus so far. The pigment migration has a dynamic range of around 4 log units and is maximally sensitive to green light. Adaptation from darkness to bright light lasts over an hour, which is slow compared to the radial pupil mechanism in some dragonflies and locusts.

How animals glide: from trajectory to morphology

Animals that glide produce aerodynamic forces that enable transit through the air in both arboreal and aquatic environments. The relative ease of gliding compared with flapping flight has led to a large diversity of taxa that have evolved some degree of flight capability. Glide paths are curved, reflecting the changing forces on the animal as it progresses through its aerial trajectory. These changing forces can be under control of the glider, which uses specific aspects of anatomy to modulate lift, drag, and rotational moments on the body. However, gliders share no single anatomical or behavioral feature, and some species are unspecialized for gliding, producing aerodynamic forces using posture and orientation alone. Animals use gliding in a broad range of ecological roles, suggesting that multiple performance metrics are relevant for consideration, but we are only beginning to understand how gliders produce and control their flight from takeoff to landing. In this review, we focus on the physical aspects of how glide trajectories are produced, and additionally discuss the range of morphologies and postures that are used to control aerial movements across the broad diversity of animal gliders.

Ontogeny of aerial righting and wing flapping in juvenile birds

Mechanisms of aerial righting in juvenile chukar partridge (Alectoris chukar) were studied from hatching to 14 days-post-hatching (dph). Asymmetric movements of the wings were used from 1 to 8 dph to effect progressively more successful righting behaviour via body roll. Following 8 dph, wing motions transitioned to bilaterally symmetric flapping that yielded aerial righting via nose-down pitch, along with substantial increases in vertical force production during descent. Ontogenetically, the use of such wing motions to effect aerial righting precedes both symmetric flapping and a previously documented behaviour in chukar (i.e. wing-assisted incline running) hypothesized to be relevant to incipient flight evolution in birds. These findings highlight the importance of asymmetric wing activation and controlled aerial manoeuvres during bird development and are potentially relevant to understanding the origins of avian flight.

The descent of ant: field-measured performance of gliding ants

Gliding ants avoid predatory attacks and potentially mortal consequences of dislodgement from rainforest canopy substrates by directing their aerial descent towards nearby tree trunks. The ecologically relevant measure of performance for gliding ants is the ratio of net horizontal to vertical distance traveled over the course of a gliding trajectory, or glide index. To study variation in glide index, we measured three-dimensional trajectories of Cephalotes atratus ants gliding in natural rainforest habitats. We determined that righting phase duration, glide angle, and path directness all significantly influence variation in glide index. Unsuccessful landing attempts result in the ant bouncing off its target and being forced to make a second landing attempt. Our results indicate that ants are not passive gliders and that they exert active control over the aerodynamic forces they experience during their descent, despite their apparent lack of specialized control surfaces.

The visual ecology of directed aerial descent in first-instar nymphs of the stick insect Extatosoma tiaratum

Many wingless insects perform directed aerial descent (DAD) to return to vegetational structures after falling. Given the complex visual environment and spatial structures of tree canopies, those visual signals used as directional cues are not fully understood. Here, we address the role of visual contrast for DAD in newly hatched nymphs of the stick insect Extatosoma tiaratum under controlled laboratory conditions. Landing preferences of gliding E. tiaratum in various visual environments were studied. We used a single vertical stripe defined by variable contrast edges to test the use of contrast consistency and sharpness. We also used aggregate patterns to examine the effects of target size and the effectiveness of luminance contrast and chromatic contrast. E. tiaratum nymphs were attracted to single stripes with well-defined edges, and particularly favored narrow dark targets. The directionality and accuracy of landing were dependent on target size. Lastly, luminance contrasts were more effective in attracting landings than were chromatic contrasts. Visual contrasts are therefore used as spatial references for landing behavior in DAD. These behaviors may enable nymphs to quickly locate dark or shaded sides of vertically oriented vegetational structures in natural habitats.

Shifts in stability and control effectiveness during evolution of Paraves support aerial maneuvering hypotheses for flight origins

The capacity for aerial maneuvering was likely a major influence on the evolution of flying animals. Here we evaluate consequences of paravian morphology for aerial performance by quantifying static stability and control effectiveness of physical models for numerous taxa sampled from within the lineage leading to birds (Paraves). Results of aerodynamic testing are mapped phylogenetically to examine how maneuvering characteristics correspond to tail shortening, forewing elaboration, and other morphological features. In the evolution of Paraves we observe shifts from static stability to inherently unstable aerial planforms; control effectiveness also migrated from tails to the forewings. These shifts suggest that a some degree of aerodynamic control and capacity for maneuvering preceded the evolution of a strong power stroke. The timing of shifts also suggests features normally considered in light of development of a power stroke may play important roles in control.

Aerodynamics of the flying snake Chrysopelea paradisi: how a bluff body cross-sectional shape contributes to gliding performance

A prominent feature of gliding flight in snakes of the genus Chrysopelea is the unique cross-sectional shape of the body, which acts as the lifting surface in the absence of wings. When gliding, the flying snake Chrysopelea paradisi morphs its circular cross-section into a triangular shape by splaying its ribs and flattening its body in the dorsoventral axis, forming a geometry with fore–aft symmetry and a thick profile. Here, we aimed to understand the aerodynamic properties of the snake's cross-sectional shape to determine its contribution to gliding at low Reynolds numbers. We used a straight physical model in a water tunnel to isolate the effects of 2D shape, analogously to studying the profile of an airfoil of a more typical flyer. Force measurements and time-resolved (TR) digital particle image velocimetry (DPIV) were used to determine lift and drag coefficients, wake dynamics and vortex-shedding characteristics of the shape across a behaviorally relevant range of Reynolds numbers and angles of attack. The snake's cross-sectional shape produced a maximum lift coefficient of 1.9 and maximum lift-to-drag ratio of 2.7, maintained increases in lift up to 35 deg, and exhibited two distinctly different vortex-shedding modes. Within the measured Reynolds number regime (Re=3000–15,000), this geometry generated significantly larger maximum lift coefficients than many other shapes including bluff bodies, thick airfoils, symmetric airfoils and circular arc airfoils. In addition, the snake's shape exhibited a gentle stall region that maintained relatively high lift production even up to the highest angle of attack tested (60 deg). Overall, the cross-sectional geometry of the flying snake demonstrated robust aerodynamic behavior by maintaining significant lift production and near-maximum lift-to-drag ratios over a wide range of parameters. These aerodynamic characteristics help to explain how the snake can glide at steep angles and over a wide range of angles of attack, but more complex models that account for 3D effects and the dynamic movements of aerial undulation are required to fully understand the gliding performance of flying snakes.

Aerodynamic characteristics of a feathered dinosaur measured using physical models. Effects of form on static stability and control effectiveness

We report the effects of posture and morphology on the static aerodynamic stability and control effectiveness of physical models based on the feathered dinosaur, [Formula: see text]Microraptor gui, from the Cretaceous of China. Postures had similar lift and drag coefficients and were broadly similar when simplified metrics of gliding were considered, but they exhibited different stability characteristics depending on the position of the legs and the presence of feathers on the legs and the tail. Both stability and the function of appendages in generating maneuvering forces and torques changed as the glide angle or angle of attack were changed. These are significant because they represent an aerial environment that may have shifted during the evolution of directed aerial descent and other aerial behaviors. Certain movements were particularly effective (symmetric movements of the wings and tail in pitch, asymmetric wing movements, some tail movements). Other appendages altered their function from creating yaws at high angle of attack to rolls at low angle of attack, or reversed their function entirely. While [Formula: see text]M. gui lived after [Formula: see text]Archaeopteryx and likely represents a side experiment with feathered morphology, the general patterns of stability and control effectiveness suggested from the manipulations of forelimb, hindlimb and tail morphology here may help understand the evolution of flight control aerodynamics in vertebrates. Though these results rest on a single specimen, as further fossils with different morphologies are tested, the findings here could be applied in a phylogenetic context to reveal biomechanical constraints on extinct flyers arising from the need to maneuver.

The stimuli evoking the aerial-righting-posture of falling pea aphids

Some wingless insects possess aerial righting reflexes, suggesting that adaptation for controlling body orientation while falling through air could have preceded flight. When threatened by a predator, wingless pea aphids (Acyrthosiphon pisum) may drop off their host plant and assume a stereotypic posture that rotates them in midair to land on their feet. The sensory information triggering aphids to assume this posture has so far been unknown. We subjected aphids to a series of tests, isolating the sensory cues experienced during free-fall. Falling aphids assumed the righting posture and landed upright irrespective of whether the experiments were carried out in the light or in complete darkness. Detachment of the tarsi from the substrate triggered the aphids to assume the posture rapidly, but only for a brief period. Rotation (mainly roll and yaw) of the body in air, in the light, caused aphids to assume the posture and remain in it throughout rotation. In contrast, aphids rotated in the dark did not respond. Acceleration associated with falling or airflow over the body per se did not trigger the posture. However, sensing motion relative to air heightened the aphids’ responsiveness to rotation in the light. These results suggest that the righting posture of aphids is triggered by a tarsal reflex, but once airborne, vision and a sense of motion relative to air can augment the response. Hence, aerial righting in a wingless insect could have emerged as a basic tarsal response and developed further to include secondary sensory cues typical of falling.

Influence of substrate orientation on feeding kinematics and performance of algae grazing Lake Malawi cichlid fishes

Lake Malawi cichlids have been studied extensively in an effort to elucidate the mechanisms underlying their adaptive radiation. Both habitat partitioning and trophic specialization have been suggested to be critical ecological axes underlying the exceptional diversification of these fishes, but the mechanisms facilitating this divergence are often unclear. For instance, in the rock-dwelling mbuna of Lake Malawi, coexistence is likely tightly linked to how and where species feed on the algae coating all the surfaces of the rocky reefs they exclusively inhabit. Yet, although mbuna species often preferentially graze from particular substrate orientations, we understand very little about how substrate orientation influences feeding kinematics or feeding rates in any group of organisms. Therefore, for three species of mbuna, we quantified feeding kinematics and inferred the rates that algae could be ingested on substrates that mimicked the top, sides, and bottoms of the algae covered boulders these species utilize in Lake Malawi. A number of differences in feeding kinematics were found among species, and several of the kinematic variables were found to differ even within species when the fish grazed from different surface orientations. However, despite their preferences for particular microhabitats, we found no evidence for clear tradeoffs in the rates that the three species were inferred to be able to obtain algae from different substrate orientations. Nevertheless, our results indicate microhabitat divergence linked to differences in feeding kinematics could have played a role in the origin and maintenance of the vast diversity of co-occurring Lake Malawi mbuna species.

Tomographic reconstruction of neopterous carboniferous insect nymphs

Two new polyneopteran insect nymphs from the Montceau-les-Mines Lagerstätte of France are presented. Both are preserved in three dimensions, and are imaged with the aid of X-ray micro-tomography, allowing their morphology to be recovered in unprecedented detail. One-Anebos phrixos gen. et sp. nov.-is of uncertain affinities, and preserves portions of the antennae and eyes, coupled with a heavily spined habitus. The other is a roachoid with long antennae and chewing mouthparts very similar in form to the most generalized mandibulate mouthparts of extant orthopteroid insects. Computer reconstructions reveal limbs in both specimens, allowing identification of the segments and annulation in the tarsus, while poorly developed thoracic wing pads suggest both are young instars. This work describes the morphologically best-known Palaeozoic insect nymphs, allowing a better understanding of the juveniles' palaeobiology and palaeoecology. We also consider the validity of evidence from Palaeozoic juvenile insects in wing origin theories. The study of juvenile Palaeozoic insects is currently a neglected field, yet these fossils provide direct evidence on the evolution of insect development. It is hoped this study will stimulate a renewed interest in such work.

Gliding flight in Chrysopelea: turning a snake into a wing

Although many cylindrical animals swim through water, flying snakes of the genus Chrysopelea are the only limbless animals that glide through air. Despite a lack of limbs, these snakes can actively launch by jumping, maintain a stable glide path without obvious control surfaces, maneuver, and safely land without injury. Jumping takeoffs employ vertically looped kinematics that seem to be different than any other behavior in limbless vertebrates, and their presence in a closely related genus suggests that gap-crossing may have been a behavioral precursor to the evolution of gliding in snakes. Change in shape of the body by dorsoventral flattening and high-amplitude aerial undulation comprise two key features of snakes' gliding behavior. As the snake becomes airborne, the body flattens sequentially from head to vent, forming a cross-sectional shape that is roughly triangular, with a flat surface and lateral "lips" that protrude ventrally on each side of the body; these may diminish toward the vent. This shape likely provides the snake with lift coefficients that peak at high angles of attack and gentle stall characteristics. A glide trajectory is initiated with the snake falling at a steep angle. As the snake rotates in the pitch axis, it forms a wide "S" shape and begins undulating in a complex three-dimensional pattern, with the body angled upward relative to the glide path. The head moves side-to-side, sending traveling waves posteriorly toward the tail, while the body (most prominently, the posterior end) oscillates in the vertical axis. These active movements while gliding are substantially different and more dynamic than those used by any other animal glider. As the snake gains forward speed, the glide path becomes less steep, reaching minimally recorded glide angles of 13°. In general, smaller snakes appear to be more proficient gliders. Chrysopelea paradisi can also maneuver and land either on the ground or on vegetation, but these locomotor behaviors have not been studied in detail. Future work aims to understand the mechanisms of production and control of force in takeoff, gliding, and landing, and to identify the musculoskeletal adaptations that enable this unique form of locomotion.