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Debates on early euprimate evolution are related to the understanding of the ecological context that promoted their unique adaptations. Currently, these discussions mainly revolve around the habitual use of the small-branch niche or the frequent utilization of wider, and probably, strongly inclined substrates by euprimate ancestors. The current fossil evidence implies a diversity of arboreal quadrupedal behaviors for these early euprimates, associated with the use of various types of substrates. However, inferring the positional behavior of early euprimates based exclusively on fossils fails to unravel the positional flexibility in terms of modes and substrate use, which is important for understanding key adaptations related to limb postures. Following previous research, we studied the positional behavior, substrate use and pedal grasping modes of the marsupial feathertail gliders to investigate patterns of arboreal behavior that may be analogous to those exhibited by early euprimate ancestors. For the purposes of the current study, we observed and filmed 15 male and 20 female captive adult feathertail gliders Acrobates pygmaeus (Marsupialia: Diprotodontia: Acrobatidae) in a large enclosure in the Nocturnal Pavilion of Nowe Zoo, Poznań, Poland. Our observations demonstrated a strong preference for small and for horizontal substrates, avoidance of large and of vertical ones, a diverse positional repertoire mainly composed of quadrupedalism, clambering, climbing and gliding, the last occurring from small and oblique and vertical substrates, and the dominant use of hallucal grasping, especially on small, horizontal and oblique substrates. We thus consider that the generalized profile of A. pygmaeus could fit in a stage where the euarchontan heritage of vertical clawed activities on large substrates has decreased in favor of the use of small moderately inclined substrates efficiently negotiated by diagonal sequence quadrupedalism and handled via an apparently powerful hallucal grasp. Competent use of small substrates could have further expanded into small vertical substrates, which would progressively serve as new climbing platforms and takeoff perches for unspecialized leaping. We feel that this stage may have occurred early in euprimate evolution, as small body size likely provided the necessary behavioral flexibility to exploit various niches. Depending on alternative scenarios, it could represent that of the common ancestor of euprimates or be rooted at the base of strepsirrhine evolution. This study underscores the important of analyzing the behavior of extant models to infer the locomotor evolution of euarchontans, primates or euprimates., (Copyright © 2018 Elsevier Ltd. All rights reserved.)

A key feature in primate evolution is a foot with a divergent opposable hallucal metatarsal bearing a large peroneal process. Extant primates are characterized by a powerful hallucal grasp-an either "euprimate" or "plesiadapoid-euprimate" ancestor acquisition-that facilitates the exploitation of fine branches, an ability that increased the fitness of ancestral euprimates. In this context, the didelphid marsupial Caluromys has been used as the extant analog to this primate morphotype stage due to some morphological, ecological, and behavioral features. However, the extent to which and the positional and support contexts in which Caluromys uses powerful hallucal grasping are not known. This renders analogies to any mode of "euprimate" or "stem primate" grasping poorly substantiated. The present paper quantifies locomotor and postural behavior, support use, and associated frequencies of hallucal grasping in captive Caluromys philander via analysis of video recordings. During locomotion, Caluromys primarily used diagonal sequence walk, clamber, and climb, whereas stand, foot-hang, and bipedal stand were the dominant postures. Small, fine, horizontal, and moderately inclined branches were frequently used. Overall rates of "apparently powerful hallucal grasps" were high, but were exceptionally high during clamber, climb, foot-hang, and bipedal stand. Additionally, an "apparently powerful hallucal grasp" was very common upon fine, small, steep, and vertical branches. The extensive use of such powerful hallucal grasping provided stability and safety that enabled Caluromys to proficiently utilize fine branches of various orientations. The ability to negotiate such unstable supports, further reflected in foot anatomy, provides evidence that the morphobehavioral complex of Caluromys can serve as an extant analog to the plesiadapoid-euprimate ancestor, represented as a terminal branch feeder with effective hallucal grasping.

Urban forests impose significant challenges to the animals that inhabit them due to the altered properties of available substrates from anthropogenic interventions. To cope with these structural peculiarities, urban species exhibit behavioral adjustments to successfully exploit the urban habitat. The present study examined habitat use and positional behavior of northern palm squirrels (Funambulus pennantii) in the urban forests of Kathmandu, Nepal, to test such behavioral modifications. Between July and August 2018, we collected focal animal instantaneous data on the behavior, locomotor/postural mode, forest layer, tree crown part, and substrate type, size, and inclination use of four different individuals. Our results indicated a primarily arboreal species, mostly using the middle canopy layers and the intermediate and central tree parts. Moreover, tree branches and artificial substrates were commonly used that were mainly large and horizontal. Locomotion was dominated by quadrupedalism and claw climb, whereas postures by quadrupedal stand, and, to a lesser extent, sit and claw cling. Most of our initial predictions were only partly supported by our findings. This behavioral idiosyncrasy most likely reflects the adaptive flexibility of the species to human-modified habitats. In this way, northern palm squirrels apparently expanded their ecological niche and successfully persisted against anthropogenic pressures throughout their range. As urban expansion is inexorable, more research is required to understand the behavioral and ecological flexibility of animals that effectively exploit these impacted habitats. [ABSTRACT FROM AUTHOR]

Simple Summary: Positional behaviors comprise the entirety of animals' locomotion and posture. Often, these positional behaviors are paired with information about sußbstrate characteristics (e.g., orientation, diameter, texture, height) and frequency to gain an ecological perspective of when and why an animal utilizes a particular behavior. Thus far, quantitative studies of positional behavior have been limited to mammals, leaving a major gap in our understanding of how animals utilize their environment. In this study, we present the first quantitative report of positional behavior within Aves, presenting scan sampling data from an established colony of Monk Parakeets (Myiopsitta monachus) from Brooklyn, New York City. Parrots exhibited a strong preference for small and terminal branches when perching arboreally. Such a pattern is consistent with arboreal primates. We also observed an increase in locomotor diversity on artificial versus naturally occurring substrates. This demonstrates the potential importance of a flexible behavioral repertoire in facilitating a successful transition towards an urban landscape in introduced species and underscores the need for further studies exploring positional behaviors among urban wildlife. Positional behaviors have been broadly quantified across the Order Primates, and in several other mammalian lineages, to contextualize adaptations to, and evolution within, an arboreal environment. Outside of Mammalia, however, such data are yet to be reported. In this study, we present the first quantitative report of positional behavior within Aves, presenting 11,246 observations of scan sampling data from a colony of Monk Parakeets (Myiopsitta monachus) from Brooklyn, New York City. Each scan recorded locomotor and postural behavior and information about weather condition, temperature, and substrate properties (e.g., type, size, orientation). A distinction was also recorded between natural and artificial substrates. Parrots exhibited a strong preference for small and terminal branches, a selection which may reflect targeted foraging of new fruit growth and leaf-buds. We further observed that the gait transition from walking to sidling appears primarily driven by substrate size, with the former preferred on the ground and on large, broad substrates and the latter used to navigate smaller branches. Finally, we observed an increase in locomotor diversity on artificial versus naturally occurring substrates. This demonstrates the importance of a flexible behavioral repertoire in facilitating a successful transition towards an urban landscape in introduced species. [ABSTRACT FROM AUTHOR]

The Vietnamese pygmy dormouse is a small, arboreal, nocturnal, blind rodent that uses incipient echolocation to navigate in tree canopies. In order to assess its arboreal faculties in relation to echolocative capacity, the present study investigated the locomotor and postural behavior of the species in a simulated arboreal environment within an enclosure. The study subjects were intensively video and audio recorded and the two sets of data were synchronized for subsequent analyses. This is the first study on the positional behavior and substrate use of the Vietnamese pygmy dormice. Our results showed that the species spent most of its time on arboreal substrates, mostly traveling and scanning. Locomotion was dominated by vertical climb and leap, occurring mostly on small vertical and on medium and large strongly inclined substrates, respectively. Locomotion and substrate type were strongly related to emission of echolocative pulses. These findings most likely suggest that echolocation compensates for poor vision to effectively negotiate highly challenging arboreal constraints, and are in favor of the arboreal origins of pygmy dormice. Moreover, such a scenario could also support the echolocation-first hypothesis for the emergence of echolocation in bats prior to active flight. [ABSTRACT FROM AUTHOR]

Colugos (order Dermoptera) are medium-sized nocturnal arboreal eutherian euarchontan mammals, which glide, climb vertically and hang from different arboreal substrates in the rainforests of Southeast Asia. Their close phylogenetic position to either Primates (as Primatomorpha) or Scandentia (as Sundatheria) renders them significant for understanding evolutionary-adaptive trends of key features within the Euarchonta (primates, scandentia, dermoptera, and plesiadapiformes). In this context, we studied foot positional, postural, and grasping patterns in relation to substrate use in free-ranging Sunda colugos (Galeopterus variegatus) in west Java, Indonesia. On large, strongly inclined substrates, colugos primarily used claw climbing and clinging activities, with a dorsiflexed, abducted, and everted foot using an abducted clawed grasp and abducted hallux. On small, less inclined substrates, colugos habitually used suspensory locomotion and postures with pedal plantarflexion, adduction, inversion, and an adducted clawed grasp and adducted hallux. The morphofunctional similarity of the colugo foot with that of early euarchontans suggests comparable behaviors at the base of euarchontan evolution. Furthermore, the functional-adaptive significance of these behaviors is further investigated under different phylogenetic scenarios, linking dermopterans to either scandentians or primates. Our findings underscore the importance of similar behavioral studies for examining functional-adaptive evolutionary scenarios. [ABSTRACT FROM AUTHOR]

Locomotion and postures are key factors to understanding the biology of animals. However, scansorial and arboreal carnivorans remain poorly studied regarding these issues. Herein, we present a behavioral and morphological analysis of the arboreal locomotion of the tayra ( Eira barbara ), a neotropical forest-dwelling mustelid. Data on habitat use and locomotor and postural modes were collected from free-ranging tayras in a terra-firme forest in French Guiana. Additionally, qualitative morphological traits and linear measurements of the girdles and appendicular skeleton were analyzed through comparative anatomical descriptions, univariate tests, and a principal components and discriminant analysis. Tayras frequently used clambering, quadrupedal walking, claw climbing and quadrupedal standing, performed primarily on small and medium, oblique and horizontal branches. Furthermore, our morpho-functional analyses revealed that tayras possess autopodial specializations for navigating on arboreal substrates, while the more proximal elements present features more similar to other terrestrial or scansorial mustelids, and theoretically less modified from the hypothetical weasel-like ancestor of mustelids. This mosaic of morphological features of the tayra, a combination of phylogenetic inertia and ecological signals, very likely evolved to promote the efficient and effective exploitation of diverse habitats and resources in this versatile species. [ABSTRACT FROM AUTHOR]

Abstract: Several hypotheses have been proposed to explain the origins of primates, suggesting evolutionary scenarios that are usually paralleled to modern mammalian models that partly simulate the morpho-behavioral apomorphies of primates. The current study examines substrate use and positional behavior of tiny-sized Eurasian harvest mice (Micromys minutus) as living models for inferring the evolution of versatile behavior, flexible branch use and pedal grasping in early small-sized primates. Micromys exhibits a diverse locomotor repertoire composed of clambering and climbing, and uses postural modes requiring secure pedal grasping. It also makes considerable use of fine flexible substrates of various inclinations during both feeding/foraging and traveling. This profile seems to represent an intermediate step between stage 2 (Tupaia-stage) and stage 3 (Caluromys-stage) in Sargis et al.''s (2007) primate evolutionary scenario. Furthermore, our findings suggest that tiny size in itself brings a unique level of flexibility in posture and locomotion that has heretofore been underappreciated in the primate evolution literature. [Copyright &y& Elsevier]

Abstract: The present report aims to quantify the use of zygodactylous (opposability of digits II to III) grasping in relation to positional modes and support size and orientation, in the highly arboreal, walking/climbing woolly opossum, Caluromys philander. For this purpose, four captive adult C. philander were intensively video-recorded and their positional behavior, hand grasp, and support size and orientation use were analyzed frame-by-frame. Overall, C. philander used a zygodactylous grasp in 81.3±1.2% of bouts. In terms of support features, this grasp was particularly common on (a) supports that could be wholly and partly held by the animals’ hand and (b) vertical supports in particular. In a comparable manner, zygodactyly dominated during above-support positional modes, but was significantly less used during bridging and suspension. The results show that zygodactyly provided an above-support secure and steady grasp on relatively unstable arboreal supports, by aligning the hand with the main axis of the support. This very likely assisted in controlling over the applied torques during cautious quadrupedal and climbing activities with extended hand contact that characterizes the locomotor strategy of C. philander. These observations need to be further tested by more detailed kinetic studies and on a larger sample of arboreal didelphids. [ABSTRACT FROM AUTHOR]

The manual and pedal grasping abilities of primates, characterized by an opposable hallux, flat nails, and elongated digits, constitute a unique combination of features that likely promoted their characteristic use of arboreal habitats. These hand and foot specificities are central for understanding the origins and early evolution of primates and have long been associated with foraging in a fine-branch milieu. However, other arboreal mammals occupy similar niches, and it remains unclear how substrate type may have exerted a selective pressure on the acquisition of nails and a divergent pollex/hallux in primates or in what sequential order these traits evolved. Here, we video-recorded 14,564 grasps during arboreal locomotion in 11 primate species (6 strepsirrhines and 5 platyrrhines) and 11 non-primate arboreal species (1 scandentian, 3 rodents, 3 carnivorans, and 4 marsupials). We quantified our observations with 19 variables to analyze the effect of substrate orientation and diameter on hand and foot postural repertoire. We found that hand and foot postures correlate with phylogeny. Also, primates exhibited high repertoire diversity, with a strong capability for postural adjustment compared to the other studied groups. Surprisingly, nails do not confer an advantage in negotiating small substrates unless the animal is large, but the possession of a grasping pollex and hallux is crucial for climbing small vertical substrates. We propose that the divergent hallux and pollex may have resulted from a frequent use of vertical plants in early primate ecological scenarios, although nails may not have resulted from a fundamental adaptation to arboreal locomotion. • Hand and foot postures of arboreal mammals correlate with phylogeny • Primates exhibit higher hand and foot postural repertoire diversity • Nails do not confer an advantage in negotiating thin substrates compared to claws • Pollex and hallux grasping ability is crucial for climbing thin vertical substrates How did nails and grasping abilities evolve in first primates? Toussaint et al. analyze autopodial postures during arboreal locomotion in various mammals. They find that primate nails may not result from a locomotor adaptation although climbing vertical substrates may have exerted a selective pressure on the acquisition of the grasping pollex/hallux. [ABSTRACT FROM AUTHOR]