Locomotor Diversity Research Articles

A new fossil cercopithecid tibia from Laetoli and its implications for positional behavior and paleoecology

Detailed analyses and comparisons of postcranial specimens of Plio-Pleistocene cercopithecids provide an opportunity to examine the recent evolutionary history and locomotor diversity in Old World monkeys. Studies examining the positional behavior and substrate preferences of fossil cercopithecids are also important for reconstructing the paleoenvironments of Plio-Pleistocene hominin sites. Here we describe a new fossil cercopithecid tibia (EP 1100/12) from the Australopithecus afarensis-bearing Upper Laetolil Beds (∼3.7 Ma) of Laetoli in northern Tanzania. The fossil tibia is attributed to cf. Rhinocolobus sp., which is the most common colobine at Laetoli. In addition to qualitative comparisons, the tibial shape of EP 1100/12 was compared to that of 190 extant cercopithecids using three-dimensional landmarks. Discriminant function analyses of the shape data were used to assess taxonomic affinity and shape variation relating to positional behavior. EP 1100/12 clustered with extant colobines, particularly the large-bodied genera Nasalis and Rhinopithecus. Comparisons reveal that EP 1100/12 belongs to a large-bodied monkey that engaged in arboreal pronograde quadrupedalism. These findings add further support to previous inferences that woodland and forest environments dominated the paleoenvironment of the Upper Laetolil Beds, which supported the diverse community of cercopithecids at Laetoli. The inferred paleoecology and the presence of large-bodied arboreally-adapted monkeys at Laetoli show that A. afarensis had access to a range of diverse habitats, including woodlands and forests. This supports the possibility that A. afarensis, with its potential range of positional capabilities, was able to utilize arboreal settings for food acquisition and refuge from predators.

Correlates between calcaneal morphology and locomotion in extant and extinct carnivorous mammals.

Locomotor mode is an important component of an animal's ecology, relating to both habitat and substrate choice (e.g., arboreal versus terrestrial) and in the case of carnivores, to mode of predation (e.g., ambush versus pursuit). Here, we examine how the morphology of the calcaneum, the 'heel bone' in the tarsus, correlates with locomotion in extant carnivores. Other studies have confirmed the correlation of calcaneal morphology with locomotion behaviour and habitat. The robust nature of the calcaneum means that it is frequently preserved in the fossil record. Here, we employ linear measurements and 2D-geometric morphometrics on a sample of calcanea from eighty-seven extant carnivorans and demonstrate a signal of correlation between calcaneal morphology and locomotor mode that overrides phylogeny. We used this correlation to determine the locomotor mode, and hence aspects of the palaeobiology of, 47 extinct carnivorous mammal taxa, including both Carnivora and Creodonta. We found ursids (bears), clustered together, separate from the other carnivorans. Our results support greater locomotor diversity for nimravids (the extinct 'false sabertooths', usually considered to be more arboreal), than previously expected. However, there are limitations to interpretation of extinct taxa because their robust morphology is not fully captured in the range of modern carnivoran morphology.

Craniodental and humeral morphology of a new species of Masrasector (Teratodontinae, Hyaenodonta, Placentalia) from the late Eocene of Egypt and locomotor diversity in hyaenodonts.

Hyaenodonta is a diverse clade of carnivorous mammals that were part of terrestrial faunas in the Paleogene of Eurasia and North America, but the oldest record for the group is Afro-Arabian, making the record there vital for understanding the evolution of this wide-spread group. Previous studies show an ancient split between two major clades of hyaenodonts that converged in hypercarnivory: Hyainailourinae and Hyaenodontinae. These clades are each supported by cranial characters. Phylogenetic analyses of hyaenodonts also support the monophyly of Teratodontinae, an Afro-Arabian clade of mesocarnivorous to hypercarnivorous hyaenodonts. Unfortunately, the cranial anatomy of teratodontines is poorly known, and aligning the clade with other lineages has been difficult. Here, a new species of the phylogenetically controversial teratodontine Masrasector is described from Locality 41 (latest Priabonian, late Eocene) from the Fayum Depression, Egypt. The hypodigm includes the most complete remains of a Paleogene teratodontine, including largely complete crania, multiple dentaries, and isolated humeri. Standard and “tip-dating” Bayesian analyses of a character-taxon matrix that samples cranial, postcranial, and dental characters support a monophyletic Masrasector within Teratodontinae, which is consistently placed as a close sister group of Hyainailouridae. The cranial morphology of Masrasector provides new support for an expanded Hyainailouroidea (Teratodontinae + Hyainailouridae), particularly characters of the nuchal crest, palate, and basicranium. A discriminant function analysis was performed using measurements of the distal humerus from a diverse sample of extant carnivorans to infer the locomotor habits of Masrasector. Masrasector was assigned to the “terrestrial” locomotor category, a result consistent with the well-defined medial trochlear ridges, and moderately developed supinator crests of the specimens. Masrasector appears to have been a fast-moving terrestrial form with a diverse diet. These specimens considerably improve our understanding of Teratodontinae, an ancient member of the Afro-Arabian mammalian fauna, and our understanding of hyaenodont diversity before the dispersal of Carnivora to the continent near the end of the Paleogene.

A novel, bounding gait in swimming turtles: implications for aquatic locomotor diversity.

Turtles are an iconic lineage in studies of animal locomotion, typifying the use of slow, alternating footfalls during walking. Alternating movements of contralateral limbs are also typical during swimming gaits for most freshwater turtles. Here, we report a novel gait in turtles, in which the pleurodire Emydura subglobosa swims using a bounding gait that coordinates bilateral protraction of both forelimbs with bilateral retraction of both hindlimbs. Use of this bounding gait is correlated with increased limb excursion and decreased stride frequency, but not increased velocity when compared with standard swimming strokes. Bounding by E. subglobosa provides a second example of a non-mammalian lineage that can use bounding gaits, and may give insight into the evolution of aquatic flapping. Parallels in limb muscle fascicle properties between bounding turtles and crocodylids suggest a possible musculoskeletal mechanism underlying the use of bounding gaits in particular lineages.

The thigh and leg of Homo naledi

This paper describes the 108 femoral, patellar, tibial, and fibular elements of a new species of Homo (Homo naledi) discovered in the Dinaledi chamber of the Rising Star cave system in South Africa. Homo naledi possesses a mosaic of primitive, derived, and unique traits functionally indicative of a bipedal hominin adapted for long distance walking and possibly running. Traits shared with australopiths include an anteroposteriorly compressed femoral neck, a mediolaterally compressed tibia, and a relatively circular fibular neck. Traits shared with Homo include a well-marked linea aspera, anteroposteriorly thick patellae, relatively long tibiae, and gracile fibulae with laterally oriented lateral malleoli. Unique features include the presence of two pillars on the superior aspect of the femoral neck and a tubercular distal insertion of the pes anserinus on the tibia. The mosaic morphology of the H. naledi thigh and leg appears most consistent with a species intermediate between Australopithecus spp. and Homo erectus and, accordingly, may offer insight into the nature of the earliest members of genus Homo. These fossils also expand the morphological diversity of the Homo lower limb, perhaps indicative of locomotor diversity in our genus.

Testing the Role of Cursorial Specializations as Adaptive Key Innovations in Paleocene-Eocene Ungulates of North America

Episodes of rapid faunal turnover in the fossil record are often used to examine processes driving macroevolutionary changes, such as competitive exclusion. The sudden appearance in the earliest Eocene of North America of artiodactyls and perissodactyls, and subsequent decline of endemic “condylarths” constitutes such an episode. It has been suggested that the specializations for high speed locomotion (cursoriality) that are present in artiodactyls and perissodactyls were key innovations of these orders accounting for their success in the Eocene and onwards. A quantitative geometric morphometric analysis of distal femoral articular morphology was used to examine changes in locomotor specializations in North American ungulates across the Paleocene-Eocene boundary. “Condylarths” were found to have displayed a broad range of locomotor adaptions, including cursoriality. The early Eocene had the broadest disparity in terms of taxonomic and locomotor contributions to morphological diversity. Changes in locomotor variety were associated with the disappearance of arboreal taxa, primarily “condylarths.” The initial impact of artiodactyls and perissodactyls in North America on existing locomotor diversity was limited and does not support a competitive exclusion hypothesis.

The postcranial skeleton of Galecyon: evidence for morphological and locomotor diversity in early Hyaenodontidae (Mammalia, Hyaenodontida)

ABSTRACTHyaenodontidae is a diverse component of the carnivorous guild in early Eocene (Wasatchian) North American mammalian faunas. Although there have been suggestions that early members of the family had diverse locomotor repertoires, few Wasatchian postcrania are adequately described. Here we describe the first known postcranial remains of the rare Wasatchian hyaenodontid Galecyon, based principally on a well-preserved partial skeleton from the Willwood Formation, Wyoming. Galecyon is reconstructed as a 5.2–7.9 kg terrestrial carnivore. Small but significant differences throughout the skeleton distinguish Galecyon from Prolimnocyon. Galecyon is reconstructed as scansorial/generalized terrestrial because these postcranial differences consistently indicate a more terrestrial habit than in the scansorial Prolimnocyon. Among other hyaenodontids, Arfia shows evidence for parallel terrestrial adaptation, whereas Pyrocyon is morphologically intermediate between Galecyon and Prolimnocyon. Manipulation of the well-preserved bones forming the crurotarsal joint of Galecyon provides evidence that contradicts a previous proposal that Arfia, another Wasatchian hyaenodontid, was capable of hind foot reversal. In both genera, movements at the crurotarsal joint were largely restricted to a parasagittal plane. Phylogenetic analysis of a new postcranial character set supports a pattern of relationships for early Eocene hyaenodontids different from that supported by dental morphology. Combining the two data partitions favors most aspects of the dental topology, but the conflict between dental and postcranial data indicates that confident phylogenetic resolution can be elusive, even with relatively dense sampling. SUPPLEMENTAL DATA—Supplemental materials are available for this article for free at www.tandfonline.com/UJVPCitation for this article: Zack, S. P., and K. D. Rose. 2015. The postcranial skeleton of Galecyon: evidence for morphological and locomotor diversity in early Hyaenodontidae (Mammalia, Hyaenodontida). Journal of Vertebrate Paleontology. DOI: 10.1080/02724634.2014.1001492.

The foot of Homo naledi.

Modern humans are characterized by a highly specialized foot that reflects our obligate bipedalism. Our understanding of hominin foot evolution is, although, hindered by a paucity of well-associated remains. Here we describe the foot of Homo naledi from Dinaledi Chamber, South Africa, using 107 pedal elements, including one nearly-complete adult foot. The H. naledi foot is predominantly modern human-like in morphology and inferred function, with an adducted hallux, an elongated tarsus, and derived ankle and calcaneocuboid joints. In combination, these features indicate a foot well adapted for striding bipedalism. However, the H. naledi foot differs from modern humans in having more curved proximal pedal phalanges, and features suggestive of a reduced medial longitudinal arch. Within the context of primitive features found elsewhere in the skeleton, these findings suggest a unique locomotor repertoire for H. naledi, thus providing further evidence of locomotor diversity within both the hominin clade and the genus Homo.

Mammalian femora across the Cretaceous–Paleogene boundary in eastern Montana

Our understanding of latest Cretaceous and earliest Paleogene mammalian evolution is based almost entirely on the dental fossil record. Mammalian postcranial fossils are rare and mostly found as isolated elements in latest Cretaceous and earliest Paleogene vertebrate microfossil assemblages of North America. Although placing these fossils in a tooth-based taxonomic framework is difficult, they can provide insight into locomotor diversity and habitat preference to complement diet reconstructions and diversity estimates from dental fossils. Here, we describe 64 femora of mammals recovered from latest Cretaceous (Lancian) and earliest Paleogene (Puercan) localities in eastern Montana. We sorted these based on morphology and size (morphotypes). In some cases, morphotypes were tentatively assigned to dentally based taxa that are known from these strata.Although our resulting femoral dataset is small relative to the study area's dental dataset, we show several key findings. First, there is a greater morphological diversity of multituberculate femora than previously recognized, especially in the latest Cretaceous sample. In contrast, metatherians, which have a high relative abundance in Lancian Hell Creek Formation dental assemblages, are absent from our postcranial samples; eutherian femora are only present in the Puercan assemblages. Second, we record a minor decrease in morphotype richness across the K–Pg boundary that is associated with an increase in mean specimen size, due to the appearance of a few significantly larger-bodied, immigrant taxa. Among the eutherians, there are two specimens of larger-bodied early Puercan archaic ungulates, a very large specimen of a middle/late Puercan taeniodont, pantodont, or triisodontid, as well as a specimen possibly attributed to a “plesiadapiform” archaic primate. Third, preliminary functional morphologic analyses of the more complete specimens suggest that locomotor diversity increased from mainly arboreal or terrestrial/saltatorial multituberculates in the latest Cretaceous to include a fossorial multituberculate and potentially an arboreal eutherian in the early Paleocene. These patterns parallel those previously reported from a dental dataset and indicate that postcranial data are valuable as an independent means to test hypotheses of taxonomic and ecomorphological diversity across the K–Pg boundary.

Terrestrial locomotion-where do we stand, where are we going? An introduction to the symposium.

Locomotion is fundamental to the survival of many animal species, and terrestrial environments are one of the primary habitats through which a wide range of animals (including humans) must move. Many recent efforts have been made to broaden the approaches and systems used to understand how terrestrial locomotion is executed and modulated. This symposium highlights these efforts and seeks to identify new directions for the study of this diverse behavior. Studies focusing on the structural and functional foundations of terrestrial locomotion, terrestrial locomotor dynamics, and terrestrial locomotor diversity point toward several promising areas for future work. These include: the development, application, and refinement of computational and robotic models; the integration of approaches to clarify which of multiple layers of selection and biological organization influence locomotor performance; increasing the taxonomic, environmental, and behavioral range of study systems to promote new research syntheses and questions; and expansion of studies from laboratory settings to examinations in the field and in the context of ontogenetic and evolutionary time. With new, integrative data from diverse systems in natural settings, new opportunities will emerge for understanding how locomotion contributes to the survival and fitness of terrestrial animals.

Wave-induced abiotic stress shapes phenotypic diversity in a coral reef fish across a geographical cline

While morphological variation across geographical clines has been well documented, it is often unclear whether such changes enhance individual performance to local environments. We examined whether the damselfish Acanthochromis polyacanthus display functional changes in swimming phenotype across a 40-km cline in wave-driven water motion on the Great Barrier Reef, Australia. A. polyacanthus populations displayed strong intraspecific variation in swimming morphology and performance that matched local levels of water motion: individuals on reefs subject to high water motion displayed higher aspect-ratio fins and faster swimming speeds than conspecifics on sheltered reefs. Remarkably, intraspecific variation within A. polyacanthus spanned over half the diversity seen among closely related damselfish species from the same region. We find that local selection driven by wave-induced abiotic stress is an overarching ecological mechanism shaping the inter- and intraspecific locomotor diversity of coral reef fishes.

Primate Feeding and Foraging: Integrating Studies of Behavior and Morphology

Given that something as fundamental as food acquisition is subject to selection pressure, it follows that morphological and behavioral diversity among primates is reflective of a range of adaptations to diet, feeding, and foraging. The recognition of these adaptations, however, is operationally difficult because it is the interaction between morphological and ecological variables that serves to define the particular adaptation. Researchers have addressed this problem of recognition of adaptation by integrating functional and biomechanical measures of morphological performance with observations of foraging and feeding behavior of primates in natural habitats. These disparate approaches traditionally resided in separate laboratory and field domains, but technological and analytical advances have blurred the distinction between them. The success with which this integration of approaches has elucidated the nature of primate foraging adaptations is reviewed with respect to (a) ingestive strategies, (b) locomotor diversity, (c) hard-object feeding in papionin primates, and (d) the influence of “fallback foods” on behavior and morphology.

AR Highlights

The December issue of the Anatomical Record is a special issue, “Evolutionary and Functional Morphology of New World Monkeys.” New World Monkeys (platyrrhines) are small to midsized primates. They currently inhabit a wide range of habitats spanning the American continents, from southern Mexico to Northern Argentina and represent almost one-third of all living primates. This special issue focuses on our primate relatives, the New World Monkeys, placing species and structures within the perspective of evolutionary change. Brain evolution in New World Monkeys is poorly understood. Questions of interest include “What is the relationship between brain size and body size?” as well as more practical issues such as “How is a reliable data set defined?” and “Who gets to determine that reliability?” New World Monkeys appear to offer a good model to determine how cognition evolves in relation to brain size based on the fact that they colonized a large but isolated continental habitat approximately 35–40 million years ago. The authors tested a basic hypothesis of the relationship between gut size and brain size in New World Monkeys. However, formulating a hypothesis is difficult when data sets are not complete, which is a common issue. The authors report on three unique data sets, focusing on the issues of brain size and gut morphology in platyrrhines. One set of data comprised of 162 individual brain weights and body weights of adult New World Monkeys. A second set comprised of 59 individuals, with measures on gut and body weight. These were compared with previously published reports of smaller samples as well as large databases derived from museum records. Their data confirmed the variations in brain size among platyrrhines, with a variety of proposed hypotheses to explain these observations. The authors also found a large variety of relative gut size and within-gut proportions, which suggest that multiple factors are involved. They suggest potential causal factors that appear to interact in different ways among outlier taxa. New World Monkeys have diverse diets and feeding strategies, which are recognized as key components of primate natural history and evolution. Therefore, morphology and function of the primate feeding apparatus have been extensively studied to relate them to diet and feeding behaviors. However, the function and evolution of the platyrrhine feeding apparatus is not completely understood. The authors reviewed several recent studies (and currently ongoing) on how the platyrrhine skull is loaded during feeding. Gaps in knowledge were identified, highlighting the need for new data, such as data on loading regimens in the platyrrhine skull during mastication. Differences between Old World and New World Monkeys suggest that Old World Monkeys may not be an appropriate model of jaw loading patterns for platyrrhines. Some of the studies indicate the need for a broader examination of morphology using new techniques and concepts. Advances in technology are likely to improve accuracy in quantifying morphology and provide new information for form–function relationships. The authors' stress that integration of approaches will provide the greatest opportunity for advancing the knowledge of platyrrhine feeding biology. A hope of the authors is that some of their ideas will initiate further advances in the understanding of the platyrrhine masticatory apparatus. Modern platyrrhines occupy diverse habitats, which has resulted in distinct morphological, ecological, and behavioral adaptations that can be broadly correlated to specific phylogenetic groups. Successful exploitation of these habitats requires a variety of positional behaviors. Therefore, the study of locomotion is important for understanding platyrrhines' adaptive diversity. The fossil record of New World Monkeys is quite scarce but there are numerous reports of their anatomy and positional behavior in living species. The authors summarize locomotor patterns for both fossil and modern New World Monkeys. However, agreement on phylogenetic relationships between fossil and modern taxa is lacking. The authors' consider two different hypotheses to explain phylogenetic patterns. The “long lineage hypothesis” states that modern New World Monkeys are characterized by a number of long-lived species that evolved from a common ancestor and the fossil taxa are actually early affiliates of these. In contrast, the “stem platyrrhine hypothesis” states that most early Patagonian fossils bear no relationships to modern species, but instead represent an earlier radiation, which is currently mostly extinct. The authors discuss that the evolution of locomotor diversity offers a lot of insight into the adaptive radiation among platyrrhines, but resolution to competing hypotheses of platyrrhine phylogeny remains to be accomplished. The authors' review is intended to stimulate recovery of more fossils and more study of the diverse modern species, as well as provide a fresh framework for asking questions.

Those feet in ancient times

A fossil foot found in Ethiopia suggests that human ancestors that walked on two feet and also ably climbed trees existed until 3.4 million years ago, adding evidence for locomotor diversity during early human evolution. See Article p.565 A 3.4-million-year-old partial skeleton of a hominin foot unearthed in Ethiopia offers an intriguing riddle. The only hominin previously known from that date was Australopithecus afarensis (to which 'Lucy' belonged), which was fully bipedal, and had essentially modern feet. The latest specimen, however, shows evidence for an opposable big toe, more like that seen in modern apes or in the hominin Ardipithecus ramidus, which lived one million years earlier. The new find suggests the coexistence of more than one hominin species in the Pliocene epoch, three to four million years ago, each with its own way of getting around.

Orangutans employ unique strategies to control branch flexibility

Orangutans are the largest habitually arboreal mammal. For them, as for all arboreal mammals, access to the abundant fruits and narrowest gaps found among the thin peripheral branches of tree crowns poses considerable safety risks and energetic demands. Most arboreal primates use flexed-limb postures to minimize problems caused by branch compliance and instability. Here, we show that Sumatran orangutans employ unique locomotor strategies to control compliance and allow access to the terminal branch niche for feeding and gap crossing. We calculated a "stiffness score," which is a measure of the flexibility of the supports on which orangutans moved. We found that certain locomotor behaviors clearly are associated with the most compliant supports; these behaviors appear to lack regular limb sequences, which serves to avoid the risk of resonance in branch sway caused by high-frequency, patterned gait. Balance and increased stability are achieved through long contact times between multiple limbs and supports and a combination of pronograde (horizontal) and orthograde (vertical) body postures, used both above branches and in suspension underneath them. Overall, adult females seem to be the most conservative in their travel, selecting more solid and secure supports than males and adolescents. These results have implications for understanding locomotor diversity in fossil and extant apes and for orangutan conservation and reintroduction programs.

PARALLEL EVOLUTION OF HAND ANATOMY IN KANGAROOS AND VOMBATIFORM MARSUPIALS: FUNCTIONAL AND EVOLUTIONARY IMPLICATIONS

Abstract: The anatomy of the mammalian hand is exposed to an intriguing interplay between phylogeny and function, and provides insights on phylogenetic affinities as well as locomotory habits of extinct species. Within the marsupial order Diprotodontia, terrestrial plantigrade quadrupedalism evolved twice, in the mostly extinct vombatiforms and in extant macropodoids. To assess the influence of functional and phylogenetic signal on the manus in these two clades, manual anatomy and digital proportions in specimens of eight extinct and three extant vombatiforms were investigated and compared with extant macropodoids and extant possums. The results reveal extensive parallelisms in the carpal region of vombatiforms and macropodoids, including flattened distal metacarpal facets, reduction of the palmar process of the hamatum, reduction of mid‐wrist joint curve, extensive hamatum/scaphoid contact, and absence of a lunatum. These transformations appear to be related to stabilization of the wrist for plantigrade locomotion. Vombatiforms are apomorphic in scaphoid and triquetrum anatomy and their metacarpals are much more gracile than in other Diprotodontia. Manual diversity is greater in vombatiforms than in macropodoids, as probably was locomotor diversity. Digital proportions as well as wrist anatomy divide the extinct vombatiforms into species resembling arboreal diprotodontians, whereas others group with terrestrial quadrupedal kangaroos and wombats. The latter is suggested to be owing to plantigrade locomotion and/or large size. Carpal anatomy and digital proportions suggest that a range of earlier diverging vombatiforms may have been arboreal or scansorial. As such, we propose that the ancestor of extant vombatiforms (koalas and wombats) may have been arboreal, an option that deserves consideration in the reconstruction of vombatiform evolution.

Kinematics of waterfall climbing in Hawaiian freshwater fishes (Gobiidae): vertical propulsion at the aquatic–terrestrial interface

AbstractTo reach adult habitats, juveniles of three species of Hawaiian gobies (fishes under 3 cm long) climb waterfalls up to 350 m high, over 10 000 times their body length. The demands of moving through such an extreme environment could constrain the range of viable locomotor mechanisms that these fishes use. Previous qualitative observations indicated that Lentipes concolor and Awaous guamensis use ‘powerbursts’ of axial undulation to climb, whereas Sicyopterus stimpsoni‘inches up’ vertical surfaces by alternately attaching oral and pelvic suckers to the substrate. To compare these propulsive mechanisms and their physiological requirements, high‐speed video footage of climbing by juveniles from these three species on an artificial waterfall were collected, and climbing kinematics and performance for the two climbing styles were quantified. Bouts of powerburst climbing by L. concolor and A. guamensis typically begin in or near direct water flow and are initiated by a single, rapid adduction of the pectoral fins. Powerburst climbing bouts are rapid (12.4±1.0 body lengths (BL) s−1), but short in duration (0.07±0.02 s) with few continuous locomotor cycles (3.8±1.3 cycles bout−1). Powerburst climbers use high amplitude undulations along the entire body, but minimum resultant velocities of these undulations are high (>6 BL s−1). This suggests that these species may hybridize terrestrial propulsive mechanisms with aquatic mechanisms. In contrast, climbing by inching in S. stimpsoni involves little axial undulation or fin movement. Sicyopterus stimpsoni typically exit the water outside of direct flow and seem to use terrestrial propulsive mechanisms. As the oral disc attaches to the substrate, it expands to almost twice its resting area, after which the posterior body is pulled upwards; once the pelvic disc attaches, the oral disc releases and the anterior body advances. Climbing bouts include several continuous cycles of disc attachment (11.0±1.4 cycles bout−1) and last several seconds at velocities of 0.21±0.01 BL s−1. Before climbing waterfalls during migration to adult habitats, S. stimpsoni undergo a non‐feeding metamorphosis that leads to the development of the mouth as a secondary locomotor organ. The unusual behaviour and ontogenetic strategy of S. stimpsoni seem to be evolutionary novelties, rather than ancestral retentions, suggesting that the evolution of these features may have been closely correlated. The substantial performance and kinematic distinctions between powerburst and inching climbing indicate that considerable locomotor diversity can evolve even in the context of extreme environmental demands.

Ecomorphology of Locomotion in Labrid Fishes

The Labridae is an ecologically diverse group of mostly reef associated marine fishes that swim primarily by oscillating their pectoral fins. To generate locomotor thrust, labrids employ the paired pectoral fins in motions that range from a fore-aft rowing stroke to a dorso-ventral flapping stroke. Species that emphasize one or the other behavior are expected to benefit from alternative fin shapes that maximize performance of their primary swimming behavior. We document the diversity of pectoral fin shape in 143 species of labrids from the Great Barrier Reef and the Caribbean. Pectoral fin aspect ratio ranged among species from 1.12 to 4.48 and showed a distribution with two peaks at about 2.0 and 3.0. Higher aspect ratio fins typically had a relatively long leading edge and were narrower distally. Body mass only explained 3% of the variation in fin aspect ratio in spite of four orders of magnitude range and an expectation that the advantages of high aspect ratio fins and flapping motion are greatest at large body sizes. Aspect ratio was correlated with the angle of attachment of the fin on the body (r = 0.65), indicating that the orientation of the pectoral girdle is rotated in high aspect ratio species to enable them to move their fin in a flapping motion. Field measures of routine swimming speed were made in 43 species from the Great Barrier Reef. Multiple regression revealed that fin aspect ratio explained 52% of the variation in size-corrected swimming speed, but the angle of attachment of the pectoral fin only explained an additional 2%. Labrid locomotor diversity appears to be related to a trade-off between efficiency of fast swimming and maneuverability in slow swimming species. Slow swimmers typically swim closer to the reef while fast swimmers dominate the water column and shallow, high-flow habitats. Planktivory was the most common trophic associate with high aspect ratio fins and fast swimming, apparently evolving six times.

Bipedalism, flight, and the evolution of theropod locomotor diversity

ABSTRACT The evolution of theropod flight has been characterized as a shift from one to three locomotor modules. Basal theropods, which were terrestrial bipeds, had a single locomotor module composed of the hind limb and tail. In birds, aerial locomotion was acquired with the origination of the wing module and a decoupling of the hind limb and tail into separate pelvic and caudal modules. This increase in modularity is thought to have granted birds more locomotor “options” than non-avian theropods. More specifically, an aerial locomotor system could have eased constraints on the hind limb and allowed specialization for habitats and lifestyles unavailable to non-birds. If so, bird hind limbs should be more disparate than those of non-avian theropods. We addressed this hypothesis by visualizing one aspect of limb design, the proportions of the three main segments, using ternary diagrams. Our results show that avian hind limb proportions are much more disparate than those of non-avian theropods. This broad range of limb design correlates with a radiation in locomotor diversity founded on three locomotor modules. We propose that birds have reached regions of proportion morphospace that are off limits to bipeds with only one locomotor module. In comparison, the limbs of non-avian theropods are conservatively proportioned. Despite great variation in body size, theropods other than birds do not exhibit specializations for locomotion other than terrestrial bipedalism. Although other aspects of size and shape need to be analyzed, the relationship between modular flexibility and morphological disparity appears to play an important role in theropod locomotor evolution.

Variation in the leaping of lemurs

Locomotor diversity among lemurids has been ignored by placing most species into a category of arboreal quadrupeds. Recent field studies have shown that leaping behaviors comprise a relatively large amount of their travel. In this contribution I detail a study of captive lemurs locomoting on a designed support network and/or in outdoor enclosures. Associations between support context, leaping behaviors, and landing kinematics are detailed for Hapalemur griseus, Eulemur rubriventer, Eulemur fulvus, Eulemur mongoz, and Varecia variegata. In-air body position, including the amount and location of trunk flexion, coupled with the extent of shoulder and hip flexion dictates limb use at landing. Limb strike pattern when landing onto the same support type varies interspecifically. The kinematic variation in leaping behaviors may well have implications for functional analyses of the postcranium. © 1996 Wiley-Liss, Inc.